The flat engine of Impreza and Forester. As with all boxers, head gasket wear is typical - oil leaks are the first sign before ignition codes appear.
Click a code for the full breakdown: symptoms, causes, and whether you can keep driving.
Random/Multiple Cylinder Misfire Detected
The engine control unit detects misfires occurring randomly across multiple cylinders, meaning combustion is failing intermittently in more than one cylinder.
System Too Lean (Bank 1)
The engine is getting too much air or too little fuel on bank 1 - the ECU has hit the limit of its ability to compensate.
Knock Sensor Circuit Malfunction
The knock sensor signal is invalid - the ECU can no longer detect detonation and retards timing defensively.
Crankshaft Position Sensor Circuit Malfunction
The ECU has lost or distrusts the crankshaft position signal - without it the engine cannot time ignition or injection.
Catalyst System Efficiency Below Threshold (Bank 1)
The downstream oxygen sensor shows the catalytic converter on bank 1 is no longer cleaning exhaust gases efficiently.
Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
A second camshaft sensor on bank 1 does not match the crankshaft position the ECU expects, pointing to a timing discrepancy on that cam.
Find a trusted repair shop nearby and book a diagnostic visit online.
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