Yukon Security Lockout: Quick Fix for Dead Engine

Had almost the same problem with my 1998 GMC Sierra, sounds very similar to your immobilizer system issue. With some experience working on car electronics, I initially thought it was the fuel pump, but it turned out to be related to the anti-theft system. The symptoms matched exactly, brief start then immediate die-off, which is typical for an ignition control problem. The workshop discovered the car immobilizer was not properly recognizing the key signal, even though the remote functions worked fine. They reprogrammed the key to properly sync with the immobilizer system. The whole fix cost 45 Euro and took about an hour. No parts replacement was needed, it was purely a programming issue. To help diagnose your specific case better: What error codes are you getting exactly? Have you noticed any warning lights on the dash? Does this happen with all keys or just one? When did the problem first start? This could save you from unnecessary repairs, as car immobilizer issues often get misdiagnosed as fuel or starter problems. The fix might be as simple as a key reprogramming like in my case.

My Yukon has 143495 KM and I just had it serviced last month. Thanks for sharing this, its making me more confident that its an immobilizer fault rather than a fuel system issue. The error codes Im getting are P1631 and P1626, which from what I understand point to theft deterrent problems. The security light flashes when this happens. It started about a week ago, first intermittently but now its constant. Happens with both keys, which makes me think its the immobilizer system itself rather than just a key programming issue. The key signal seems fine for unlocking, but clearly something is wrong with the ignition control communication. Planning to take it to a shop that specializes in security systems since this seems beyond basic diagnostics. Has anyone else faced these specific error codes with similar symptoms?

Good to hear back about your Yukon situation. I remember when my Sierra showed similar symptoms, those error codes you mentioned (P1631 and P1626) are exactly what I saw too. The fact that its happening with both keys definitely points to the immobilizer system rather than individual key issues. After my key reprogramming fix worked for a few weeks, the problem actually came back. The shop then found the immobilizer control module itself was failing. They had to perform a proper immobilizer bypass and reprogram the entire system. Cost more than the initial fix (around 280 Euro) but solved it permanently. Since your security light is flashing, and both keys are affected, you might be looking at the same root cause. Taking it to a security system specialist is smart, regular shops often struggle with these specific car electronics issues. Curious though, have you noticed if the problem gets worse in certain weather conditions? With my Sierra, it was always worse on cold mornings before the fix. This can help the technician pinpoint if its purely electronic or if theres a temperature-related component issue. Would definitely recommend getting it checked soon before it leaves you stranded completely. These symptoms tend to get progressively worse with GM immobilizer systems of that era.

The P1631 and P1626 codes combined with the flashing security light are really helpful confirmations, at least I know Im dealing with the anti-theft system and not chasing down fuel problems. Your experience with the Sierra matches my situation almost exactly. The problem does seem worse in the morning, now that you mention it. By afternoon its a bit more likely to start, though still unreliable. Getting the immobilizer system checked by specialists next week, booked an appointment after reading about your experience with the failing control module. Im prepared for the possibility of needing a full immobilizer bypass if reprogramming doesnt fix it. Better to spend the 280 Euro and solve it properly than keep having starting issues. Really dont want to end up stranded somewhere when the system fails completely. Thanks for the detailed info about your repair experience, its given me a much clearer picture of what to expect and helped confirm Im on the right track with the security system diagnosis rather than looking at fuel delivery problems.