# BCM not Talking to ECU?



## xanat05 (Aug 16, 2019)

Hi all!

Recently put another motor into a 2010 1.8 Automatic Cruze - swapped out the master wiring harness straight onto the freshly installed engine - but got nothing when trying to start (black dash)

After continuity checks all over from an Auto-electrician they believe its the BCM not talking to the ECU (even though continuity if fine between them) and they believe the BCM is gone - but this will mean having to replace the whole lot? BCM/ECU/Key cant be keyed to each other....talking big money on an older car?


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## Snipesy (Dec 7, 2015)

There’s like 20 ECUs on the car. I think you mean ECM.

The BCM controls off/run/crank which is what everything uses to power on. With the ECM unplugged you still get a dash, radio, etc

So either the BCM isn’t powered at all or your key is not working. Start by checking BCM fuses. I really doubt the BCM is actaully dead.

Even if all the security checks failed, and the key is invalid, as long as it turns it will switch into run mode (the engine just won’t start).


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## RoninDusette (Aug 21, 2018)

xanat05 said:


> Hi all!
> 
> Recently put another motor into a 2010 1.8 Automatic Cruze - swapped out the master wiring harness straight onto the freshly installed engine - but got nothing when trying to start (black dash)
> 
> After continuity checks all over from an Auto-electrician they believe its the BCM not talking to the ECU (even though continuity if fine between them) and they believe the BCM is gone - but this will mean having to replace the whole lot? BCM/ECU/Key cant be keyed to each other....talking big money on an older car?


I recently went through something similar. I spent almost 2 days non stop checking every **** wire and fuse and relay. HP Tuners wouldn't connect, and I had the same issue as you (though coupled with other random stuff). Battery was just replaced, I have the big three which I took out and put back in, and replaced/reinforced the negative battery to chassis cable... no change.

I went out the next day and leaned slightly on the top of the engine compartment fuse box... there was some life. I removed it, checked for damage, and reseated it VERY well, and torqued the shi+ out of the 3 bolts that hold it in. Boom. No issues since. They tend to vibrate loose, especially if they have been messed with before. It's hella easy. Take a volt/multimeter, hook the - side to the negative battery cable/terminal, turn the car to on, and check the fusesm, both sides from the strut side forward. You may find that you had the same problem as I did.


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