The other day I had a late 90’s GM in the shop. The owner had recently bought it from a small car lot, and had no idea of the history of the vehicle. It was one of those “great deals” that he couldn’t pass up. Why is it these great deals always have some sort of catch to them? Maybe it would be a good idea to have it checked out before you buy it. After looking at it, I might tell you to “pass it up.” Honestly, I’ll never understand why someone will buy a used car when they know nothing about it, or decide after they buy it to finally have it checked out … but they do.
This particular creation had some strange problems. It had a strange battery drain. At first glance all the instrument cluster warning lights, interior lights, and all the electrical functions seemed to be working correctly, but there was a drain strong enough to drain the battery in a day or so. Finding the solution was going to lead to an even bigger problem.
Narrowing it down by watching the amp meter for the parasitic draw value, and pulling fuses till the numbers dropped back into factory specs was the next procedure. Of all things, it ended up back to a crossed up circuit between the air bag system and the charging system. I decided to check the air bag system for codes.
This was interesting, it was offline. No communication with the crash box. Hmmm, I’m a little confused, because I know I saw the air bag light come on and go off when I pulled it into the shop. Turning the key off, and then restarting the car didn’t help me much, because the air bag light was on and then off. But then again, maybe it did help. Like I said, the light came on, and then went off … Hey, wait a minute isn’t there supposed to be a few seconds before it goes off? Isn’t this how it verifies its systems are functioning properly? So, what’s going on here?
As a technician I’m trying to follow the codes, the diagnostic charts, and the operating description of the system I’m working on. This particular problem wasn’t following any typical scenarios. Take into account this whole thing started off because of a battery drain … I’m really starting to scratch my head over this one.
I had a lot of different ways to go with this one. I could try and follow the draw a little further, or I could chase the problem from the air bag side of it. Maybe, it will all lead to the same problem. I think I’ll work on it from the air bag side of the problem.
The air bag fuses were all good, and the light did come on in the dash. So, I decided to pull the air bag diagnostic module out and pin check the leads to see if that would go anywhere. My first check on any system is the positive signals and then the grounds. Why? Because a loss of ground can be seen as an open lead, and if the positive signals are there, you’ll actually find a voltage signal on the open ground. That’s what electricity wants to do: find ground, and take the shortest path back to the source of the voltage.
In this case they were all there, but when I checked the leads to the instrument cluster the voltage was coming towards the crash box rather than to the cluster. What now? (Here it’s helpful to remember: I love my job, I love my job, repeat as necessary.) I guess I better pull the cluster and check the wiring from there back to the crash box and see if that goes anywhere.
After pulling the dash it didn’t take a rocket scientist to see what the problem was. On the back of the instrument cluster somebody had cut the circuit board line to the air bag light, and then added a soldered-on wire to the charge light. So when the charge light was on, so was the air bag light. Once the car started (provided the charging system is working correctly) the charge light would go out, and so would the air bag light. Huh???
You can imagine my “mechanical language” was not for the faint of heart when I found out what was going on. It seems some genius didn’t want to replace the air bag module, so they invented their own air bag warning light instead. Brilliant stupidity… I think that’s the best way to explain it. I can’t imagine somebody went through all the trouble to deceive the buyer of this car for a safety issue such as air bags. It should be a criminal offense and it is in some states. (See adjacent article for new penalties in California.)
After undoing the homemade airbag light, the draw was completely gone. Now the only thing to do was to replace the air bag module to bring it back up to working order.
Leave it to some unscrupulous dork out there to try something like this. I’m not saying anybody would have caught the problem at first glance. It was a well thought out deception. If you were not intentionally looking for an air bag light delay, I don’t think you would have caught the problem. But, I still think it is a good idea to have any car checked out prior to buying it. Maybe, just maybe, you can spot problems like this before you own the problem.