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Q: ECM stays on after key is off

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I have a 1995 MITSUBISHI ECLIPSE GS (non-turbo) with a very peculiar issue. It had a parasitic draw since the day I bought it used and eventually it fried the ECM. I recently replaced the ECM and the car runs great. The problem I have is after I shut the car off I can hear a high frequency coming from the ECM, indicating that it is running or possibly shorting out. It's also notable that disconnecting the negative battery cable or pulling the ECM fuse will stop the sound and turn the ECM off, and interestingly enough, when reconnected after a few seconds it does not turn itself back on. The ECM only turns back on again when the key is inserted and set to the on position. I'm sure you can see my dilemma, having pop the hood and pull a fuse every time I'm done driving to save the battery and possibly the ECM. If anyone has an Idea of what I can check or look for, I will forever be in your debt.

My car has 119121 miles.
My car has an automatic transmission.

A: If the old ECM wasn’t making the same noise...

If the old ECM wasn’t making the same noise, I would say the problem is in the new ECM. Based on the year of the car, I am guessing this was a used ECM. If this is the case, try to find another one, even if it’s just to try swapping it for awhile. It’s likely that the used ECM you got is no good, which is part of the problem with buying used parts. It’s also possible that it could be a failed ECM relay, so you could get a new relay for pretty cheap and swap it in for good measure. If you swap the ECM and relay and this still happens, then you should have the problem diagnosed by a qualified technician, such as one available from YourMechanic. They may also be able tohelp you determine if there are any more parasitic drains on your battery.

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