Trouble shooting ECM & Security Lock

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TYF Newbie
Jan 30, 2023
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Hey there Y'all,

I'll put the full story below, but I was wanting to know if there was a way to trouble shoot a ECM and the security lock on a 2003 Chevy Tahoe. I have a OBD scanner that can't connect to the Tahoe, but will to other vehicles. The security lock is constantly on when I try to turn on the vehicle, but it won't start so I'm not sure if it's a bad ECM or an issue where the anti-theft lock is keep me form accessing the ECM. Has anyone else had issues with their Tahoe not starting and being unable to use a OBD scan tool?

Story Time:
I learned that I had an issue when I tried to move the truck, but found out it wouldn't start with no crank or sound what so ever. The dash would turn on for me to see the gear, and mileage. If I took the keys out the car would turn off, but headlights would stay on for some reason. I was going on vacation in the hour so I didn't have time to fix, fast forward 1 week I replaced the battery because the old one was bad. Replaced that and the main relays in the fuse box. Tested all fuses and saw they're good. Tested the ones lodged on the driver side panel and found they were good as well. I was able to use 2 wires wrapped around a dummy fuse to ignition relay and was able to get the truck to crank. I've tried several times testing with a OBD scan tool, but it can't connect to the Tahoe (used 2 different ones, 1 bluetooth & 1 wired). Not sure what else I can do so any insight would be greatly appreciated.

Joseph Garcia

Supporting Member
Aug 2, 2018
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Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me will chime in.

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