An oft misdiagnosed check engine light on a wide range of Toyota, Lexus and Scions is code P0606- ECM/PCM Processor Malfunction. More often than not, the culprit is NOT the ECM/PCM assembly but rather the sensing or heater circuits in the air/fuel ratio or oxygen sensors. We went more into diagnosing a failed air/fuel ratio sensor in this post. A technician can diagnose the P0606 code fairly easily by checking the freeze frame data out of the ECM/PCM when the problem was detected. Some things to look for include:
- Air/fuel ratio sensor (normally sensor 1) or oxygen sensor (normally sensor 2) heater circuit out of specification for 1-2 frames ONLY. Sometimes the heater circuit will intermittently open or develop high resistance. A resistance of many thousands of Ohms is an indicator of this, or drastic jump in resistance that only last for a few frames of data after the car is warmed up
- Air/fuel ratio sensor or oxygen sensor data is out of range. Toyota air/fuel ratio sensor operate between 0 and 5 volts, oxygen sensors between 0 and 1 volt. Anything above 5 volts indicates a problem that requires further investigation.
- Air/fuel ratio sensor abnormal behavior, not enough to set a “Stuck lean” or “Stuck rich” code, but freeze frame data indicating jumps in voltage quickly for only a few frames (faster than normal response).
If you have a P0606 – ECM/PCM Processor Malfunction code in addition to other check engine P codes (especially if they are air/fuel or oxygen sensor codes), repair the other codes before addressing the P0606. More often than not the P0606 is a false positive.
As Eden Prairie and Chanhassen’s Toyota and Lexus repair specialist, we hope this helps a DIY or auto mechanic alike avoid an unnecessary ECM/PCM replacement!
Can the Toyota dealer know exactly it is the ecm with p606 code? The car ran fine, the technician has checked for bad wire connection, and said it was the computer. after the computer is replaced, the code came back on. Now, he said it’s the bad oxygen sensor. Could that be misdiagnosed?
While possible, it is unlikely the ECM had failed in conjunction with the oxygen sensor. I’ve yet to see a P0606 that was the ECM – it has always been an oxygen sensor failure in those I’ve diagnosed. It is possible however, so I’d defer to the diagnosis technician on this particular case.
I have a Toyota dealer telling me the P0606 code is a bad ECM. It started with hesitation on startup (very low idle for 2 seconds), mainly when the car had been sitting for a couple hours. If the car had just been turned off or sat overnight, it would start fine. Then it finally threw a P2013 code. I replaced the throttle body, and then the P0606 code started coming on with the same hesitation on start up. I am very skeptical that it is the ECM and it has been difficult to get people to think outside the troubleshoot table. Any suggestions?