Subaru Impreza Fault Codes & Engine Codes explained

2001 Onwards Imprezas use the ODB2 protocol for on-board ECU diagnostics and reporting of sensor and operating faults.

In general the system works well, sensors that fail or operate outside a set range or beyond a threshold will illuminate the CEL and store a record of the fault on the ECU with an associated faultcode. The ECU’s onboard memory will store a seperate list of both current and historic codes, so even if the CEL goes out there will be a record of the fault to assist in diagnosing the problem. Certain fault codes that are considered to be of a more serious nature, when triggered will put the ECU into a “Limp Mode” which can introduce a lower rev limit, reduced boost levels (and power output) and increased fuel consumption. t’s important to have any EML faults diagnosed and repaired promptly to keep your engine operating efficiently and safely.

We have a wealth of experience and a range of comprehensive diagnostic tools to rectify any Engine Management, ABS or Airbag faults you may be experiencing with your Subaru.

Common Impreza Fault Codes

Listed below are some of the more commonly experienced faultcodes on the Impreza –

P0030 – HO2S Heater Control Circuit (Bank1 Sensor1)
P0031 – HO2S Heater Control Circuit Low (Bank1 Sensor1)
P0032 – HO2S Heater Control Circuit High (Bank1 Sensor1)
P0130 – O2 Sensor Circuit (Bank1 Sensor1)
P0131 – O2 Sensor Circuit Low Voltage (Bank1 Sensor1)
P0132 – O2 Sensor Circuit High Voltage (Bank1 Sensor1)
P0133 – O2 Sensor Circuit Slow Response (Bank1 Sensor1)
P0134 – O2 Sensor Circuit No Activity (Bank1 Sensor1)
P0135 – O2 Sensor Heater Circuit (Bank1 Sensor1)

Primary Lambda Sensor Fault Codes

These codes all relate to the Primary Lambda sensor which is found in the RHS of the exhaust manifold on all UK WRX and STi Turbo models, and in the exhaust downpipe (behind the turbo) in all 2003> JDM STi models
Fairly commom fault, give the age of the sensor. It’s important to replace with the correct Denso Sensor for trouble free future operation – Many of the aftermarket and pattern sensors that are available do not work correctly.

P0136 – O2 Sensor Circuit Malfunction (Bank1 Sensor2)
P0137 – O2 Sensor Circuit Low Voltage (Bank1 Sensor2)
P0138 – O2 Sensor Circuit High Voltage (Bank1 Sensor2)
P0139 – O2 Sensor Circuit Slow Response (Bank1 Sensor2)
P0141 – O2 Sensor Heater Circuit (Bank1 Sensor2)

Secondary Lambda Sensor Fault Codes

These codes all relate to the Secondary Lambda sensor, which is located behind the catalytic convertors, just in front of the exhaust centre section join
Used by the ECU to validate Catalytic Convertor activity, and can be completely disabled if your car is fully decatted.

P0117 – Engine Coolant Temp Circuit Low Input
P0118 – Engine Coolant Temp Circuit High Input

Located in the Coolant Cross Pipe (behind the alternator) this sensor provides the ECU with coolant temperature information which is critical for Cooling Fan operation and warmup/overheating strategies
Fuel Consumption can get very high if the CTS reads incorrectly

P0171 – System Too Lean (Bank1)
P0172 – System Too Rich (Bank1)

Both these codes are somewhat generic, and indicative of an underlying problem needing further investigation.
They are triggered when Closed Loop Airflow adaptation values become pegged at their minimum/maximum limits.
Commonly, but not only caused by failing MAF sensor, post maf air leak, boost leak, Mapping fault, Unmapped Induction Kit, Faulty fuel Pump, FPR vacuum reference hose split, faulty Primary Lambda Sensor, and various other issues.

P0244 – Turbo Wastegate Solenoid ‘A’ Range/Performance

This code is triggered when the ECU detects an overboost condition (the value is adjustable and programmed into the ecu) and is often accompanied with a Boost Cut condition (a momentary hesitation in power delivery)
Can be attributed to a faulty or blocked Boost Control Solenoid (BCS), Blocked boost restrictor pill/orifice (on a factory 2 port setup), Split vacuum hose between the Turbo and Solenoid or Solenoid and Actuator, Unmapped exhaust modifications (specifically catalytic convertor removal), Mapping issue

P0301 – Cylinder #1 Misfire Detected
P0302 – Cylinder #2 Misfire Detected
P0303 – Cylinder #3 Misfire Detected
P0304 – Cylinder #4 Misfire Detected

Cylinder specific codes indicating a misfire.
Can be a faulty/worn sparkplug, failed coilpack, cylinder compression issue.
Any of these codes can also be generated by a faulty Neutral Position Switch (NPS)

P0325 – Knock Sensor Circuit Fault (Bank1)
P0327 – Knock Sensor Circuit Low Input (Bank1)
P0328 – Knock Sensor Circuit High Input (Bank1)

The knock sensor is a microphone which is tuned to a specific frequency range, which gives the ECU feedback on detonation, and located on top of the engine block, on the passenger side.
Visible if you look down between the intercooler and the inlet manifold, but easier to get to with the TMIC removed.

P0335 – Crankshaft Position Sensor (SensorA)
P0336 – Crankshaft Position Sensor Range/Performance (SensorA)
P0340 – Camshaft Position Sensor (SensorA)
P0341 – Camshaft Position Sensor Range/Performance (SensorA)

Cam and Crank Sensor related faults. Crank sensor is located in the oil pump housing (front centre of the engine, underneath the alternator). Cam Sensor (on pre 2006 models) is located on the top of the LH cylinder Head, next to the engine oil dipstick.

P0365 – Camshaft Position Sensor ‘B’ (Bank1)
P0390 – Camshaft Position Sensor ‘B’ (Bank2)

Found on all 2001> STi models and 2006> WRX the ‘B’ Cam sensors are used to report on AVCS cam postion. Inlet cam sensors are located on the top of the cylinder heads at the rear, and connected to the engine wiring harness with a short link loom.

P0420 – Catalyst System Below Threshold

This code commonly features on unmapped cars running a decatted exhaust system. Always disabled and mapped out with an FB Tuning remap.

P0500 – Vehicle Speed Sensor
P0501 – Vehicle Speed Sensor Range/Performance
P0502 – Vehicle Speed Sensor Circuit Low Input
P0503 – Vehicle Speed Sensor Intermittant/Erratic/High

Located on the RH side of the gearbox, the VSS gives a speed signal to the Speedometer and the ECU.
This fault is rarely seen on any UK model cars, but more common on JDM variants that have been fitted with a speedo convertor for kmh->mph conversion. Normally the fault can be attributed to the aftermarket convertor or associated wiring.
Imposes a 4000rpm rev limit when the fault is current.

P0506 – Idle Control System Lower Than Expected
P0507 – Idle Control System Higher Than Expected
P0508 – Idle Control System Circuit Low
P0509 – Idle Control System Circuit High

The Idle Control Valve is located on the throttle body. It is a rotary design, and it’s operation can be affected by the buildup of oil which restricts movement of the blade. Can be stripped and cleaned and will require a neplacement o-ring gasket when reassmbled.

P0545 – Exhaust Gas Temp Sensor Circuit Low (bank1)
P0546 – Exhaust Gas Temp Sensor Circuit High (bank1)

2001-2005 Impreza WRX and some Forester Turbo models are fitted with an EGT sensor in the exhaust Uppipe (pre Turbo)
The tip can break off this sensor and damage the exhaust wheel of the turbocharger.
Advisable to remove this sensor in conjunction with fitting a decatted uppipe and mapping out these codes when tuning for more power

P0562 – System Voltage Low
P0563 – System Voltage High

Either of these codes indicate a charging related problem which can usually be attributed to a faulty alternator
An ECU that has been mapped with an incorrect ROM file can also generate these codes

P1086 – TGV #2 Circuit Low
P1087 – TGV #2 Circuit High
P1088 – TGV #1 Circuit Low
P1089 – TGV #1 Circuit High
P1090 – TGV System #1 Valve open
P1091 – TGV System #1 Valve closed
P1092 – TGV System #2 Valve open
P1093 – TGV System #2 Valve closed
P1094 – TGV Signal #1 Open
P1095 – TGV Signal #1 Short
P1096 – TGV Signal #2 Open
P1097 – TGV Signal #2 Short

Tumble Generator Valve related faults. Fitted to all 2001-2005 WRX and some Forester Turbo models and 2006> WRX and STi. These are butterfly valves in the inlet manifold (similar to the throttle plate) that are partially closed at low throttle opening to increase gas speed into the inlet ports of the cylinder heads and promote better atomisation of the injected fuel. Faults can occur with the position sensors and solenoids, and the throttle plates and spindles can get stuck. Faults can be easily and cheaply overcome by pegging the butterflys wide open (or replacing with TGV deletes from a 2001-2005 STi model) and disabling all related fault codes.

P1306 – OCV Solenoid Signal 1 Malfunction Open
P1307 – OCV Solenoid Signal 1 Malfunction Short
P1308 – OCV Solenoid Signal 2 Malfunction Open
P1309 – OCV Solenoid Signal 2 Malfunction Short
P0365 – Camshaft Position Sensor B Bank 1
P0390 – Camshaft Position Sensor B Bank 2

AVCS / VVT related codes for all 2001> Impreza Sti and 2006> WRX and Forester XT models,