Common Toyota engine diagnostic codes include P0171, P0402 and P0446. A P0171 diagnostic code indicates the system is too lean, a P0402 diagnostic code indicates there is excessive exhaust gas recirculation flow, and a P0446 diagnostic code indicates there is an evaporative emission control system control circuit malfunction.Continue Reading
To troubleshoot a P0171 Toyota diagnostic code, try cleaning the mass air flow sensor and the lines running to and from it. Also inspect all the lines, including the vacuum and PCV hoses, for kinks and cracks.
To troubleshoot a P0402 diagnostic code, test the differential pressure feedback sensor. If this doesn't work, remove the EGR valve, bypass tube, and check for debris or leaks.
To troubleshoot a P0446 diagnostic code, test the vent valve circuit from the electronically commutated motor to the valve. Also check resistance on the control circuit against the models manual specifications. If this doesn't work, replace the vent valve, and reset the ECM/powertrain control module codes.Learn more about Engine