The 2001 Subaru Forester Obd2 Error Codes List is a valuable resource for diagnosing potential issues with your vehicle. OBD2-SCANNER.EDU.VN offers a comprehensive guide to understanding these codes, helping you identify the root cause of the problem and explore effective solutions. This article provides an in-depth look at common OBD2 codes for the 2001 Subaru Forester, their potential causes, and how to address them.
Contents
- 1. What Are the Most Common 2001 Subaru Forester OBD2 Error Codes?
- 1.1. P0420: Catalyst System Efficiency Below Threshold
- 1.2. P0171: System Too Lean Bank 1
- 1.3. P0300: Random/Multiple Cylinder Misfire Detected
- 1.4. P0102: Mass Air Flow (MAF) Sensor Circuit Low Input
- 1.5. P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
- 2. Comprehensive 2001 Subaru Forester OBD2 Error Codes List
- 2.1. Understanding Code Severity
- 2.2. Tools for Diagnosing OBD2 Codes
- 3. How to Use an OBD2 Scanner on a 2001 Subaru Forester
- 3.1. Choosing the Right OBD2 Scanner
- 3.2. Interpreting OBD2 Data
- 4. Addressing Common OBD2 Error Codes on a 2001 Subaru Forester
- 4.1. P0420: Catalyst System Efficiency Below Threshold
- 4.2. P0171: System Too Lean Bank 1
1. What Are the Most Common 2001 Subaru Forester OBD2 Error Codes?
The most common 2001 Subaru Forester OBD2 error codes often relate to engine performance, emissions, and sensor malfunctions. These include codes such as P0420 (Catalyst System Efficiency Below Threshold), P0171 (System Too Lean Bank 1), and P0300 (Random/Multiple Cylinder Misfire Detected). Understanding these common codes is the first step in diagnosing and resolving issues.
- P0420: Catalyst System Efficiency Below Threshold
- P0171: System Too Lean Bank 1
- P0300: Random/Multiple Cylinder Misfire Detected
- P0102: Mass Air Flow (MAF) Sensor Circuit Low Input
- P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
1.1. P0420: Catalyst System Efficiency Below Threshold
P0420 indicates that the catalytic converter is not functioning as efficiently as it should, failing to reduce harmful emissions effectively. According to the EPA, catalytic converters must reduce hydrocarbons, carbon monoxide, and nitrogen oxides by significant margins. Several factors can trigger this code:
- Defective Catalytic Converter: The converter itself may be worn out or damaged.
- Faulty Oxygen Sensors: Malfunctioning O2 sensors can provide incorrect readings, leading to a false P0420 code.
- Exhaust Leaks: Leaks in the exhaust system can affect the readings and performance of the catalytic converter.
- Engine Misfires: Misfires can cause unburnt fuel to enter the exhaust system, overloading the catalytic converter.
- Downstream O2 Sensor Issues: Problems with the downstream O2 sensor can also trigger this code.
1.2. P0171: System Too Lean Bank 1
P0171 signifies that the engine is running lean, meaning there is too much air and not enough fuel in the air-fuel mixture. According to a study by the University of California, lean conditions can lead to increased engine wear and reduced performance. Common causes include:
- Vacuum Leaks: Leaks in vacuum hoses or intake manifold gaskets can allow excess air into the engine.
- Faulty MAF Sensor: A malfunctioning MAF sensor can provide incorrect airflow readings to the engine control unit (ECU).
- Fuel Delivery Issues: Problems with fuel injectors, fuel pump, or fuel filter can restrict fuel flow.
- Oxygen Sensor Problems: Faulty O2 sensors can cause the ECU to misinterpret the air-fuel mixture.
- PCV Valve Leaks: A leaking PCV valve can also introduce extra air into the system.
1.3. P0300: Random/Multiple Cylinder Misfire Detected
P0300 indicates that the engine is experiencing random or multiple misfires, where one or more cylinders are not firing correctly. According to the National Institute for Automotive Service Excellence (ASE), misfires can lead to reduced fuel economy, rough idling, and potential engine damage. Possible causes include:
- Worn Spark Plugs: Old or damaged spark plugs can fail to ignite the air-fuel mixture properly.
- Faulty Ignition Coils: Malfunctioning ignition coils can prevent spark plugs from firing.
- Vacuum Leaks: Vacuum leaks can disrupt the air-fuel mixture in multiple cylinders.
- Low Fuel Pressure: Insufficient fuel pressure can cause misfires across multiple cylinders.
- Compression Issues: Low compression in one or more cylinders can prevent proper combustion.
1.4. P0102: Mass Air Flow (MAF) Sensor Circuit Low Input
P0102 means the Mass Air Flow (MAF) sensor is reporting a lower than expected voltage signal back to the ECU. This can lead to incorrect fueling and poor engine performance.
- Damaged Wiring: Issues in the MAF sensor circuit.
- Faulty MAF Sensor: The MAF sensor.
- Loose Connections: Poor connections.
1.5. P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
P0128 indicates that the engine coolant temperature is not reaching the required level within a specified amount of time.
- Defective Thermostat: A thermostat that is stuck open.
- Coolant Temperature Sensor Issues: A faulty sensor.
- Cooling System Problems: Issues in the cooling system.
2. Comprehensive 2001 Subaru Forester OBD2 Error Codes List
Below is a comprehensive list of OBD2 error codes for the 2001 Subaru Forester, complete with potential causes for each code:
| Code | Description | Possible Causes |
|---|---|---|
| P0010 | Camshaft Position Actuator Circuit/Open (Bank 1) | Powertrain Control Module (PCM) failure, Variable valve timing actuator failure, Wiring issue |
| P0011 | Camshaft Position – Timing Over-Advanced or System Performance (Bank 1) | Camshaft variable timing solenoid failure, Low engine oil level, Incorrect engine timing, Wrong engine oil, Variable valve timing actuator failure |
| P0012 | Camshaft Position – Timing Over-Retarded (Bank 1) | Camshaft variable timing solenoid failure, Low engine oil level, Incorrect engine timing, Wrong engine oil, Variable valve timing actuator failure |
| P0013 | Camshaft Position Actuator Circuit/Open (Bank 2) | Powertrain Control Module (PCM) failure, Variable valve timing actuator failure, Wiring issue |
| P0014 | Camshaft Position – Timing Over-Advanced or System Performance (Bank 2) | Camshaft variable timing solenoid failure, Low engine oil level, Incorrect engine timing, Wrong engine oil, Variable valve timing actuator failure |
| P0101 | Mass Air Flow (MAF) Sensor Range/Performance | Large vacuum leaks, Split Intake Air Boot or PCV Hose, Defective intake manifold gaskets, Mass Airflow Sensor (MAF) issue |
| P0102 | Mass Air Flow (MAF) Sensor Circuit Low Input | Unplugged or damaged wiring, Loose or corroded electrical terminals, Faulty MAF Sensor |
| P0113 | Intake Air Temperature Sensor Circuit High Input | Defective Intake Air Temperature Sensor, Dirty air filter, Defective Mass Air Flow Sensor, Faulty wiring or connections |
| P0128 | Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) | Defective Engine Thermostat, Defective Engine Coolant Temperature Sensor, Defective Cooling System, Low Engine Coolant |
| P0135 | O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1) | Defective Oxygen Sensor/Air Fuel Ratio Sensor, Exhaust System Leak, Intake Air System leak, Low Fuel Pressure |
| P0171 | System Too Lean (Bank 1) | Control module software update needed, Vacuum leaks, Mass air flow sensor issue, Plugged fuel filter or weak fuel pump |
| P0174 | System Too Lean (Bank 2) | PCM software update needed, Vacuum leaks, Faulty Mass Airflow (MAF) Sensor, Plugged Fuel Filter or weak Fuel Pump |
| P0200 | Injector Circuit Malfunction | Defective Fuel Injector, Faulty or corroded Fuel Injector, wiring issues, Plugged Fuel Injector |
| P0201 | Cylinder 1 Injector Circuit Malfunction | Defective Fuel Injector, Faulty or corroded Fuel Injector, wiring issues, Plugged Fuel Injector |
| P0202 | Cylinder 2 Injector Circuit Malfunction | Malfunction of the Fuel Injector, PCM Fuel Injector driver circuit malfunction, Defective wiring/connections |
| P0203 | Cylinder 3 Injector Circuit Malfunction | Fuel injector failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P0205 | Cylinder 5 Injector Circuit Malfunction | Fuel injector failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P0300 | Random/Multiple Cylinder Misfire Detected | Worn spark plugs, ignition wires, coil issues, Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure |
| P0301 | Cylinder 1 Misfire Detected | Worn spark plugs, ignition wires, coil issues, Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure |
| P0302 | Cylinder 2 Misfire Detected | Worn spark plugs, ignition wires, coil issues, Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure |
| P0303 | Cylinder 3 Misfire Detected | Worn spark plugs, ignition wires, coil issues, Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure |
| P0304 | Cylinder 4 Misfire Detected | Worn spark plugs, ignition wires, coil issues, Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure |
| P0401 | Exhaust Gas Recirculation Flow Insufficient Detected | Restriction in the EGR passages, Defective EGR Valve, Lack of proper vacuum or electrical signal to the EGR valve |
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) | Inefficient Catalytic Converter(s), Defective Front or Rear Oxygen Sensor(s), Misfiring engines |
| P0430 | Catalyst System Efficiency Below Threshold (Bank 2) | Defective Catalytic Converter, Internal engine damage resulting in high oil consumption, Leaking Head Gasket |
| P0440 | Evaporative Emission Control System Malfunction | Missing fuel cap, Defective or damaged fuel cap, Distorted or damaged Fuel Tank Filler Neck, Torn or punctured Evaporative system hose(s) |
| P0441 | Evaporative Emission Control System Incorrect Purge Flow | Missing fuel cap, Stuck open or closed purge valve, Defective or damaged fuel cap, Distorted, damaged or cracked Fuel Tank Filler Neck |
| P0442 | Evaporative Emission Control System Leak Detected (Small Leak) | Defective or damaged fuel cap, Distorted or damaged Fuel Tank Filler Neck, Small tear in the Evaporative system hose(s) |
| P0455 | Evaporative Emission Control System Leak Detected (Large Leak) | Missing fuel cap, Defective or damaged fuel cap, Distorted or damaged Fuel Tank Filler Neck, Torn or punctured Evaporative system hose(s) |
| P0500 | Vehicle Speed Sensor Malfunction | Defective Vehicle Speed Sensor, Defective Speedometer, Vehicle Speed Sensor wiring or connector issues, Communication (CAN) bus problems |
| P0501 | Vehicle Speed Sensor Range/Performance | Defective Vehicle Speed Sensor, Defective Speedometer, Vehicle Speed Sensor wiring or connector issues, Communication (CAN) bus problems |
| P0505 | Idle Air Control System Malfunction | Defective Idle Air Control Motor, Intake Manifold Vacuum leaks, Carbon buildup in the Throttle Body air passages |
| P0506 | Idle Air Control System RPM Lower Than Expected | Defective/sticking Idle Air Control Motor, Intake Manifold Vacuum leaks, Carbon buildup in the Throttle Body air passages |
| P0507 | Idle Air Control System RPM Higher Than Expected | Defective/sticking Idle Air Control Motor, Intake Manifold Vacuum leaks, Carbon buildup in the Throttle Body air passages, Defective Coolant Temperature Sensor |
| P0600 | Serial Communication Link Malfunction | Defective PCM (Power Train Control Module), Defective PCM data bus wiring/connections, Defective PCM data bus ground circuit(s) |
| P0601 | Internal Control Module Memory Check Sum Error | Lack of proper voltage to the PCM, Defective PCM memory module, Defective PCM ground circuit(s) |
| P0602 | Control Module Programming Error | Powertrain Control Module (PCM) failure, Wiring issue |
| P0603 | Internal Control Module Keep Alive Memory (KAM) Error | Lack of proper voltage to the Keep Alive Memory connection on the PCM, Defective PCM Keep Alive Memory Module (KAM), Defective PCM ground circuit(s) |
| P0605 | Internal Control Module Read Only Memory (ROM) Error | Lack of proper voltage and/or ground to the PCM, Defective PCM ROM memory module, Defective PCM ground circuit(s) |
| P0700 | Transmission Control System Malfunction | Defective Shift Solenoids, Defective Engine Coolant Temperature Sensor, Defective Valve Body, Dirty transmission fluid |
| P0705 | Transmission Range Sensor Circuit Malfunction (PRNDL Input) | Defective Transmission Range Sensor (PRNDL input), Defective wiring or connector, Defective Valve Body, Defective manual shift valve linkage |
| P0706 | Transmission Range Sensor Circuit Range/Performance | Defective Transmission Range Sensor (PRNDL input), Defective wiring or connector, Defective Valve Body, Defective manual shift valve linkage |
| P0720 | Output Speed Sensor Circuit Malfunction | Defective Output Speed Sensor, Defective Shift Solenoids, Defective Engine Coolant Temperature Sensor, Defective Valve Body |
| P0730 | Incorrect Gear Ratio | Defective Shift Solenoids, Defective Engine Coolant Temperature Sensor, Defective Valve Body, Dirty transmission fluid |
| P0841 | Transmission Fluid Pressure Sensor/Switch “A” Circuit Range/Performance | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission fluid pressure sensor failure, Wiring issue |
| P0842 | Transmission Fluid Pressure Sensor/Switch “A” Circuit Low | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission fluid pressure sensor failure, Wiring issue |
| P0845 | Transmission Fluid Pressure Sensor/Switch “B” Circuit | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission fluid pressure sensor failure, Wiring issue |
| P0846 | Transmission Fluid Pressure Sensor/Switch “B” Circuit Range/Performance | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission fluid pressure sensor failure, Wiring issue |
| P0847 | Transmission Fluid Pressure Sensor/Switch “B” Circuit Low | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission fluid pressure sensor failure, Wiring issue |
| P0901 | Clutch Actuator Circuit Range/Performance | Clutch master cylinder failure, Clutch solenoid failure, Transmission Control Module (TCM) failure |
| P0935 | Hydraulic Pressure Sensor Circuit Range/Performance | Hydraulic power unit assembly failure, Transmission Control Module (TCM) failure, Wiring issue |
| P0942 | Hydraulic Power Unit Malfunction | Hydraulic power unit assembly failure, Transmission Control Module (TCM) failure, Wiring issue |
| P0944 | Hydraulic Pressure Unit Loss of Pressure | Clogged transmission filter, Low transmission fluid level, Transmission oil pump failure, Wiring issue |
| P0961 | Pressure Control Solenoid “A” Control Circuit Range/Performance | Transmission shift solenoid failure |
| P0A08 | DC/DC Converter Status Circuit | Inverter/converter assembly failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P0A0D | High Voltage System Inter-Lock Circuit | High voltage safety device failure, Inverter/converter assembly failure, Power management control module failure |
| P0A0F | Engine Fails to Start | Hybrid transaxle assembly failure, Internal engine failure, Power management control module failure |
| P0A7F | Battery Module Deterioration | Poor connections at the HV battery, A problem with the HV battery, ECU issues |
| P0A80 | Replace Hybrid Battery Pack | High voltage battery assembly failure |
| P0B22 | Battery Contactor “A” Circuit/Open | Battery contactor assembly failure, Battery Energy Control Module (BECM) failure |
| P0B24 | Hybrid/EV Battery Voltage Sense “A” Circuit Range/Performance | Battery Energy Control Module (BECM) failure, High voltage battery assembly failure, Wiring issue |
| P0B26 | Hybrid/EV Battery Voltage Sense “A” Circuit High | Battery Energy Control Module (BECM) failure, High voltage battery assembly failure, Wiring issue |
| P0B28 | Hybrid/EV Battery Voltage Sense “A” Circuit Low | Battery Energy Control Module (BECM) failure, High voltage battery assembly failure, Wiring issue |
| P0B30 | Hybrid/EV Battery Voltage Sense “B” Circuit | Battery Energy Control Module (BECM) failure, High voltage battery assembly failure, Wiring issue |
| P0C00 | Drive Motor “A” Generator Inverter Performance | Drive motor generator power inverter control module failure |
| P0C09 | Drive Motor “A” Generator Position Sensor | Drive motor generator assembly failure, Drive motor generator power inverter control module failure |
| P0C11 | Drive Motor “A” Generator Coolant Temperature Sensor Circuit | Coolant system leak, Drive motor generator power inverter control module failure, Engine cooling fan failure, Water pump failure |
| P0C14 | Drive Motor “A” Generator Coolant Temperature Sensor Circuit Range/Performance | Coolant system leak, Drive motor generator power inverter control module failure, Engine cooling fan failure, Water pump failure |
| P0C15 | Drive Motor “A” Generator Coolant Temperature Sensor Circuit High | Coolant system leak, Drive motor generator power inverter control module failure, Engine cooling fan failure, Water pump failure |
| P2000 | NOx Adsorber Efficiency Below Threshold Bank 1 | Diesel Particulate Filter (DPF) failure, Intake air leak, Mass Airflow (MAF) sensor is dirty/loss of calibration |
| PP2002 | Diesel Particulate Filter Efficiency Below Threshold Bank 1 | Diesel Particulate Filter (DPF) failure, Intake air leak, Mass Airflow (MAF) sensor is dirty/loss of calibration |
| P2004 | Intake Manifold Runner Control Stuck Open Bank 1 | A failed IMRC actuator, A problem with the intake manifold or linkage, Wiring issues |
| P2006 | Intake Manifold Runner Control Stuck Closed Bank 1 | Intake manifold runner control actuator failure, Powertrain Control Module (PCM) failure, Restricted vacuum lines |
| P2101 | Throttle Actuator Control Motor Circuit Range/Performance | Accelerator Pedal Position (APP) assembly failure, Powertrain Control Module (PCM) failure, Throttle control motor failure, Wiring issue |
| P2122 | Throttle/Pedal Position Sensor/Switch “D” Circuit Low Input | Accelerator Pedal Position (APP) assembly failure, Powertrain Control Module (PCM) failure, Throttle control motor failure, Wiring issue |
| P2135 | Throttle/Pedal Position Sensor/Switch “A” / “B” Voltage Correlation | Accelerator Pedal Position (APP) assembly failure, Powertrain Control Module (PCM) failure, Throttle Position Sensor (TPS) failure, Wiring issue |
| P2138 | Throttle/Pedal Position Sensor/Switch “D” / “E” Voltage Correlation | Accelerator Pedal Position (APP) assembly failure, Powertrain Control Module (PCM) failure, Throttle Position Sensor (TPS) failure, Wiring issue |
| P2181 | Cooling System Performance | Engine coolant heater failure, Engine coolant level is too low, Thermostat failure |
| P2210 | NOx Sensor Circuit Malfunction Bank 1 | NOx sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2213 | NOx Sensor Circuit Malfunction Bank 2 | NOx sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2237 | O2 Sensor Positive Current Control Circuit Open Bank 1 Sensor 1 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2238 | O2 Sensor Positive Current Control Circuit Shorted to Ground Bank 1 Sensor 1 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2251 | O2 Sensor Negative Current Control Circuit Open Bank 1 Sensor 1 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2302 | Ignition Coil “A” Secondary Circuit | Ignition coil failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2303 | Ignition Coil “B” Secondary Circuit | Ignition coil failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2305 | Ignition Coil “C” Secondary Circuit | Ignition coil failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2308 | Ignition Coil “D” Secondary Circuit | Ignition coil failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2310 | Ignition Coil “E” Secondary Circuit | Ignition coil failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2401 | Evaporative Emission System Leak Detection Pump Control Circuit Low | Evap leak detection pump failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2402 | Evaporative Emission System Leak Detection Pump Control Circuit High | Evap leak detection pump failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2422 | Evaporative Emission System Vent Valve Stuck Closed | EVAP vent valve failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2431 | Secondary Air Injection System Air Flow/Pressure Sensor Circuit Range/Performance | Air control solenoid failure, Powertrain Control Module (PCM) failure, Secondary Air System pressure sensor failure, Wiring issue |
| P2432 | Secondary Air Injection System Air Flow/Pressure Sensor Circuit | Air control solenoid failure, Powertrain Control Module (PCM) failure, Secondary Air System pressure sensor failure, Wiring issue |
| P2500 | Charging System Voltage Low | Alternator failure, Battery failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2501 | Charging System Voltage High | Alternator failure, Battery failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2503 | Charging System Voltage Low | Alternator failure, Battery failure, Wiring issue |
| P2509 | ECM/PCM Power Input Signal Intermittent | Powertrain Control Module (PCM) failure, Powertrain Control Module (PCM) power relay failure, Wiring issue |
| P250C | Engine Oil Level Sensor Circuit Range/Performance | Oil level sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2601 | Coolant Pump “A” Control Circuit/Open | Coolant Heat Storage (CHS) water pump failure, Coolant Heat Storage (CHS) water pump relay, Powertrain Control Module (PCM) failure, Wiring issue |
| P2607 | Intake Air Heater “B” Control Circuit Low | Intake air heater, Powertrain Control Module (PCM) failure, Wiring issue |
| P2609 | Intake Air Heater “B” Performance | Intake air heater, Powertrain Control Module (PCM) failure, Wiring issue |
| P2610 | Internal Engine Off Timer Performance | An internal PCM problem, A problem with the PCM power or ground circuit |
| P2614 | Camshaft Position Output Circuit | Broken tone ring, Camshaft Position Sensor (CMP) failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2706 | Transmission Friction Element “E” Apply Time Range/Performance | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission shift solenoid failure, Wiring issue |
| P2711 | Unexpected Mechanical Gear State | Internal transmission failure, Transmission Control Module (TCM) failure, Transmission fluid level is low, Transmission solenoid failure |
| P2714 | Pressure Control Solenoid “D” Performance or Stuck Off | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission shift solenoid failure, Wiring issue |
| P2716 | Pressure Control Solenoid “D” Electrical | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission shift solenoid failure, Wiring issue |
| P2723 | Pressure Control Solenoid “E” Control Circuit Range/Performance | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission shift solenoid failure, Wiring issue |
| P2803 | Transmission Turbine Speed Sensor “B” Circuit | Powertrain Control Module (PCM) failure, Transmission Control Module (TCM) failure, Transmission range sensor failure, Wiring issue |
| P2806 | Transmission Range Sensor Adjustment | Powertrain Control Module (PCM) failure, Transmission Control Module (TCM) failure, Transmission range sensor failure, Wiring issue |
| P2809 | Pressure Control Solenoid “F” Control Circuit | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission pressure control solenoid failure, Wiring issue |
| P2810 | Pressure Control Solenoid “F” Performance or Stuck Off | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission pressure control solenoid failure, Wiring issue |
| P2815 | Pressure Control Solenoid “G” Control Circuit | Transmission Control Module (TCM) failure, Low transmission fluid level, Transmission pressure control solenoid failure, Wiring issue |
| P2A00 | O2 Sensor Circuit Range/Performance Bank 1 Sensor 1 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2A01 | O2 Sensor Circuit Range/Performance Bank 1 Sensor 2 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2A03 | O2 Sensor Circuit Range/Performance Bank 2 Sensor 1 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2A04 | O2 Sensor Circuit Range/Performance Bank 2 Sensor 2 | Exhaust leak, Oxygen sensor failure, Powertrain Control Module (PCM) failure, Wiring issue |
| P2BA8 | NOx Exceedence – Root Cause Unknown | Faulty NOx Sensors, NOx Sensors harness is open or shorted, NOx Sensors circuit poor electrical connection, Faulty Diesel Particulate Filter (DPF) |
| P3000 | Battery Voltage Sense Circuit Range/Performance | Fuel level is too low, High voltage battery assembly failure, High voltage battery is not sufficiently charged |
| P3100 | Drive Motor Inverter System Malfunction | High voltage powertrain control module failure |
| P3400 | Cylinder Deactivation System Malfunction | Faulty Cylinder Deactivation System |
| P3401 | Cylinder 1 Deactivation/Intake Valve Control Circuit/Open | Engine oil level is too low, Powertrain Control Module (PCM) failure, Variable valve timing solenoid failure, Wiring issue |
| B0081 | Driver Air Bag Circuit Open | Wiring issues, Control module problems, A problem with the airbag |
| C0040 | Right Front Wheel Speed Sensor Circuit Malfunction | A faulty wheel speed sensor, A problem with the wheel speed sensor circuit, Reluctor issues, A problem with the ABS module |
| U0001 | High Speed CAN Communication Bus | A faulty wheel speed sensor, A problem with the wheel speed sensor circuit, Reluctor issues, A problem with the ABS module |
| U0073 | Control Module Communication Bus Off | A faulty control module, A problem with the CAN bus |
| U0100 | Lost Communication With ECM/PCM “A” | A faulty PCM, A problem with the control module circuit, A problem with the CAN bus |
| U0107 | Lost Communication With Throttle Actuator Control Module | A dead battery, A faulty TAC module, A problem with TAC module circuit, A problem with the CAN bus |
| U0121 | Lost Communication With Anti-Lock Brake System (ABS) Control Module | A dead battery, A faulty ABS module, A problem with ABS module circuit, A problem with the CAN bus |
2.1. Understanding Code Severity
OBD2 codes can indicate a range of problems, from minor issues to severe malfunctions that require immediate attention. The severity of the code is crucial in determining the urgency and scope of the necessary repairs. Codes can generally be categorized into three levels of severity:
- Minor: These codes often indicate issues that do not pose an immediate threat to the vehicle’s operation but should be addressed to prevent further damage.
- Moderate: These codes suggest problems that can affect the vehicle’s performance and fuel efficiency. Addressing them promptly can prevent more significant issues.
- Severe: These codes indicate critical malfunctions that can cause significant damage to the engine or other vital systems. Immediate repair is necessary to prevent further damage and ensure safety.
2.2. Tools for Diagnosing OBD2 Codes
Diagnosing OBD2 codes requires the right tools and knowledge. Here are some essential tools for diagnosing OBD2 codes:
- OBD2 Scanner: This is the primary tool for retrieving and clearing OBD2 codes.
- Multimeter: Useful for testing electrical circuits and sensor outputs.
- Vacuum Gauge: Helps identify vacuum leaks, which can cause various engine problems.
- Fuel Pressure Tester: Measures fuel pressure to diagnose fuel delivery issues.
- Scan Tool with Live Data: Advanced scan tools can display real-time data from various sensors, aiding in diagnosis.
3. How to Use an OBD2 Scanner on a 2001 Subaru Forester
Using an OBD2 scanner on your 2001 Subaru Forester is a straightforward process that can save you time and money by helping you diagnose issues early. According to a study by the AAA, using an OBD2 scanner can help car owners save an average of $100 on diagnostic fees. Here’s a step-by-step guide:
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Locate the OBD2 Port: The OBD2 port is typically located under the dashboard on the driver’s side.
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Plug in the Scanner: With the ignition off, plug the OBD2 scanner into the port.
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Turn on the Ignition: Turn the ignition to the “on” position, but do not start the engine.
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Power on the Scanner: The scanner should power on automatically. If not, ensure it has batteries or is properly connected.
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Read the Codes: Follow the scanner’s instructions to read the stored codes. The scanner will display any trouble codes present.
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Record the Codes: Write down the codes and their descriptions for further investigation.
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Clear the Codes (Optional): If you wish to clear the codes after recording them, follow the scanner’s instructions. Be cautious when clearing codes, as it may erase valuable diagnostic information.
3.1. Choosing the Right OBD2 Scanner
Selecting the right OBD2 scanner can significantly enhance your diagnostic capabilities. There are several types of scanners available, each with its own features and benefits:
- Basic Scanners: These scanners provide basic code reading and clearing functions, suitable for simple diagnostics.
- Mid-Range Scanners: These offer additional features such as live data streaming, freeze frame data, and enhanced code definitions.
- Professional Scanners: These advanced scanners offer comprehensive diagnostics, including bidirectional control, advanced sensor testing, and vehicle-specific functions.
3.2. Interpreting OBD2 Data
Interpreting OBD2 data requires understanding the meaning of the codes and their potential causes. Here are some tips for interpreting OBD2 data effectively:
- Research the Codes: Use reliable sources such as OBD2-SCANNER.EDU.VN to research the meaning of each code.
- Consider the Symptoms: Consider the symptoms the vehicle is exhibiting, as they can provide valuable clues about the underlying issue.
- Check for Related Codes: Look for related codes that may provide additional information about the problem.
- Use Live Data: Utilize live data streaming to monitor sensor values and identify anomalies.
- Consult a Professional: If you are unsure about interpreting the data or performing repairs, consult a professional mechanic.
4. Addressing Common OBD2 Error Codes on a 2001 Subaru Forester
Once you have retrieved and interpreted the OBD2 codes, the next step is to address the underlying issues. Here are some common OBD2 codes and steps to resolve them:
4.1. P0420: Catalyst System Efficiency Below Threshold
Possible Solutions:
- Check Oxygen Sensors: Test the oxygen sensors to ensure they are functioning correctly. Replace if necessary.
- Inspect Exhaust System: Look for leaks in the exhaust system and repair any leaks found.
- Evaluate Catalytic Converter: Assess the catalytic converter’s condition. If it is damaged or worn out, replace it.
4.2. P0171: System Too Lean Bank 1
Possible Solutions:
- Check for Vacuum Leaks: Inspect vacuum hoses and intake manifold gaskets for leaks. Repair or replace as needed.
- Clean or Replace MAF Sensor: Clean the MAF sensor using a MAF sensor cleaner. If cleaning doesn’t
