# How does one know ECM has failed



## WhiteXtrail (Jun 30, 2012)

I have read through a number of threads and notice that there seems to be no direct error code for an ECM failure or partial failure. I have a 2005 Xtrail that starts and idles but accelerator will not work until car warms up and I restart the engine. There are no error codes so I am suspecting a ECM malfunction. Is this usually a matter of deduction or is there some sure method of knowing the ECM is not working properly. 
Thank you


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## smj999smj (Jan 1, 2006)

Just because there is something wrong and the ECM does not set a code doesn't mean the ECM is at faulty. It simply means that the ECM has not detected a problem. ECM failure is actually pretty rare as long as it is not exposed to water or other contamination or a victim of someone reverse-jumping a battery. The determination of a bad ECM is often, as you put it, "a matter of deduction" after performing the diagnostic steps in the service manual for your particular problem.


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## WhiteXtrail (Jun 30, 2012)

A note to all those who have had a similar problem as my first thread. What happened to my Xtrail was that the alternator failed. But it failed in an unusual way. When I would start the car the alternator would put out 20volts way to high for the computer system so the system would shut down to protect itself and only allowing an idle. When the engine warmed up the voltage would drop back to a normal 12 to 14 volts. This would allow me to shut of the engine a few times and the computer would reset it self and I could run the engine as normal. Hope this helps others. Have a great ride.


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## Williamt (Feb 20, 2021)

WhiteXtrail said:


> I have read through a number of threads and notice that there seems to be no direct error code for an ECM failure or partial failure. I have a 2005 Xtrail that starts and idles but accelerator will not work until car warms up and I restart the engine. There are no error codes so I am suspecting a ECM malfunction. Is this usually a matter of deduction or is there some sure method of knowing the ECM is not working properly.
> Thank you


Please I have the same problem here 2007


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## 302831 (Nov 17, 2020)

Ecu does not communicate with scan tool


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