Toyota 2002 Echo P0171 Misfire Diagnosis: Fixed After Injector Replacement, How Long for CEL to Clear?
My 2002 Toyota Echo is showing a P0171 fault code (Rich Air-Fuel Mixture - Bank 1). I've already replaced the air filter and mass airflow sensor (MAF), reset the Check Engine Light (CEL), but the engine still runs rough and the CEL returns. I checked fuel pressure — normal. No vacuum or exhaust leaks detected. Replaced both oxygen sensors, reset the CEL again — problem persists. Then I replaced all four fuel injectors. Since then, the engine runs smoothly. However, I no longer have access to a scan tool and can't reset the CEL manually. The question is: if the underlying issue has been resolved, how many drive cycles might it take for the ECU to clear the P0171 code on its own? Any insight into whether this code will eventually clear or if further diagnostics are needed would be greatly appreciated.
Try replacing the intake manifold gasket. A bad gasket can cause vacuum leaks, leading to misfires and P0171 codes. Remove the CEL reset and let the ECU learn the correct air-fuel mixture over several drive cycles — this will confirm if the issue is truly resolved.