Key relearn/ No Security light on?

THETAHOE08

MEMBER
2008 CHEVROLET TAHOE
5.3L
V8
2WD
AUTOMATIC
220,000 MILES

I replaced the ECM and Throttle body/Throttle Position Sensor and tried the key relearn process and it didn’t work.

The Security light on the dash isn’t staying on at all during the relearn process. It turns off with the rest of the lights 20 seconds or so after turning the key to run position.

Is it possible that the key relearn process isn’t working due to a bad Ignition lock cylinder which would also cause the security light not to work? The cylinder gets jammed and has trouble turning sometimes.

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
42,959 POSTS

Yes, that is possible the ignition switch could be inhibiting the relearn. Can I ask if you had the new ECM programmed before you installed it? If not, this could be why the system is not working. Here is a guide to help you see what I am talking about, you can get a preprogrammed unit by searching Google or Ebay.

https://www.2carpros.com/articles/how-to-replace-a-vehicles-main-engine-computer-pcm-ecm-ecu

Here is how to change out the ignition switch and instructions on how to replace the ECM correctly. Check out the images (below). Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.

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Wednesday, June 7th, 2023 AT 10:08 AM

THETAHOE08

MEMBER
3 POSTS

I got the ECM new with programming on it. Programmed to my VIN and last ECM I had. The security light isn’t staying on like it’s supposed to but also my Ignition lock cylinder gets jammed up and is hard to turn sometimes.

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Wednesday, June 7th, 2023 AT 11:00 AM

KEN L

MASTER CERTIFIED MECHANIC
42,959 POSTS

Yep, the ignition switch can cause the problem are having did you get a chance to change it out?

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Friday, June 9th, 2023 AT 10:13 AM

THETAHOE08

MEMBER
3 POSTS

I haven’t had the chance to change it out yet with a new one. I’ve heard yes and no on it fixing the issue. I’ve also heard that a new key would fix the problem with it jamming up like it does. I also heard that as long as the key turns to the on position then the relearn process should work but the main problem is the security light/theft deterrent isn’t coming on like it’s supposed to. If it’d come on, I’m sure the key relearn process would work.

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Friday, June 9th, 2023 AT 10:30 AM

KEN L

MASTER CERTIFIED MECHANIC
42,959 POSTS

That is true, but if the ignition switch is coming apart it can cause the key lock to jam and not supply power correctly as well. But I think we should do a CAN scan; you can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

Here is a guide to help:

https://youtu.be/u-4syLc-ifQ

and

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Here is one for about $99.00 if you need it:

https://amzn.to/3ZixY4v

Please go over these guides and get back to us. It could be the BCM is not working, and the CAN scan will detect that.