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When a replacement ECM doesn't want to make nice with the keys

Wednesday, June 27, 2018 - 07:00
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Have you ever heard the saying "Fool me once, shame on you. Fool me twice, shame on me?" or "Sometimes I'm my own worst enemy?" I'm sure we can all relate to having said both of those at one time or another. I had reason recently to have to use each saying while working on a 2004 Cadillac CTS (DM). Actually, it was the SECOND time working on the same car, with a similar problem each time, where I screwed up the most. I promise there will NOT be a third time, and I’ll share with you my experience so that hopefully, you won’t be using those sayings in the future.

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The Cadillac CTS

As a preface, when an ECM is replaced on almost every GM vehicle built since 1990, the replacement module will have to be programmed. In most cases, after module programming, there will be a need to perform additional functions in order to make the new module work correctly in the vehicle in which it was installed. One of those functions may be VTD (Vehicle Theft Deterrent) Relearn, where a module or the ignition key(s) will be registered to work in this vehicle. Over the years GM has developed several different types of VTD systems, but if we have the factory tools for the vehicles on which we work and if needed, a Locksmith’s Identification (LSID) certification, there should be nothing that would be a problem for us to do.

Patience is a virtue

It seems problems are more likely to occur if you are in a hurry. Taking time to research an anti-theft relearn on a GM would use up valuable time when it was already late on a Friday afternoon. Besides, I thought, this car is no different than all the rest in this same year range, so it should be a piece of cake! Yes, I jinxed myself again.

I had worked with the shop owner and his tech over the phone during the previous week in an effort to help them determine what the cause of the engine misfire was. The ECM had failed to drive the fuel injector in cylinder number four anymore, which necessitated replacement of the module. The shop owner knew the replacement needed to be programmed and asked what my schedule looked like. Initially he was ecstatic to learn that he might be able to ship the car before the weekend.

By 6 p.m. that day, my laptop's battery was running low and so was my patience! The programming of the “new” ECM went smoothly, without any problems. Afterwards, I tried to perform the VTD Relearn — several times, using several different methods — and still the starter would not crank the engine. There was a displayed message on the Driver Information Center (DIC): “Starting Disabled Remove Key,” indicating the ignition key being used was incorrect as well as the notorious P1631 DTC present in the ECM. Apologetically, I left the car right where it was and promised the shop owner that I would do research over the weekend to determine what I could have been doing wrong or determine what else may be causing the problem.

This is displayed if the VTD is enabled for any reason.

When I was unable to get the car started so they could ensure there were no other problems related to the customer complaint, it was disappointing for them as well as for me. They had to make the call to the vehicle owner, I had to leave empty handed (and with a bit less pride) and I now had a freshly-modified schedule for my weekend plans.

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