Reverse Lights On constantly

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Alan Crosby, Aug 19, 2013.

  1. Alan Crosby

    Alan Crosby Member

    I noticed today that the reverse lights were on all the time on my 2007 Suburban. This has happened before but locking the car and unlocking the car usually made the problem go away. As a precaution, I disabled the exit lighting feature and that seemed to work for several months, until today.

    I tried everything I could think of to turn them off, including disconnecting the battery. But as soon as I reconnected it the lights came back on. I even tried removing the trailer backup fuse (fuse 10). I finally had to remove the fuse for the vehicle backup lights (Fuse 15).

    I did notice one other strange behavior from the vehicle this morning. When we pulled out of the driveway, the windshield washers would fire off about every ten seconds. I finally had to stop the vehicle and restart it to make that stop.

    The vehicle has some other strange symptoms periodically, but this is the latest.

    Any suggestions on where to look? I didn't see any relays in the fuse block relating to the reverse lights.
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Hmm you might need to get a diagnostic with a GM diagnostic tool but I suspect you have an issue with BCM.
  3. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    The BCM does things based upon outside input, in other words, you turn on the light switch, the BCM turns on the lights. @tbplus 10 is right, there may be a problem with the BCM; but, there might be a problem with the reverse light input.

    I don't remember where the signal comes from. When things were simpler, it came from the transmission, it may still. I would check the wiring at the transmission connector.
  4. Alan Crosby

    Alan Crosby Member

    Does the BCM handle Stabilitrak too? Periodically, the light for that will go on, but only for a minute or so and then it goes off. If during that minute I happen to stop and then take off again, the shift to 2nd is quite hard. Now that I recognize what's going on, I try and drive gently during that time until it goes off.

    If these are separate systems, I wonder if I have a bigger problem with the voltage regulator. On another thread a while back I asked about pulsing headlights and it seemed like one of the diodes may be bad. If the DC voltage is noisy I wonder if that could be causing all the random electrical glitches. That problem didn't seem to be affecting anything, but now I'm not so sure.
  5. Alan Crosby

    Alan Crosby Member

    UPDATE: I didn't mention this in this thread, but I have suspected that the alternator was going bad. I would see pulsing on the headlights and interior lights periodically. It didn't suspect that it would be contributing to these problems since they occur when the engine is off. However, I thought that AC noise is probably not healthy for all these DC components, so I thought I would tackle that issue before I started replacing things.

    So I replaced the alternator this weekend, and most if not all of my other electrical gremlins have cleared up.

    Since my last post on this topic, the TPMS started complaining. At first it was one tire that was reporting 26 PSI, but then all four had no readings. After replacing the alternator, I didn't see the warning light, but I still didn't have any pressures. I relearned the tire positions and all was well.

    I thought I would put the fuse for the reverse lights back in and see what happened. They weren't immediately on like they had been, so things looked promising here too. I threw the transmission into reverse and voila! The lights were on!

    It is still something of a mystery to me why things were acting crazy on just the battery, but I am glad that things seem to be back to normal.
  6. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Sounds like a bad ground.

    When changing the alt, you may have fixed a poor connection at the battery.
  7. Alan Crosby

    Alan Crosby Member

    Well, it's back. As before, the reverse lights started staying on, and at first locking the car or starting it would clear the problem. Now, it is back to staying on constantly.

    I went to the local auto parts store to see if they had a BCM and how much it would cost. After describing the problem to the guy at the counter, he suggested replacing the reverse light relay. It was a $17 part instead of a $300 part, so I agreed. The only problem is that I can't find it. After looking at some online wiring diagrams, it looks to me that the part in question is the BCK/UP LAMPS PCB RELAY in the underhood fuse block. As far as I can tell, that is a PCB built into the fuse block and cannot be replaced without replacing the whole fuse block.

    Can anyone confirm this?

    The reason I no longer suspect the BCM is that I removed the fuse for the BCM and that did not turn the light off. I'm not sure if that is a valid assumption or not, but the wiring diagram shows the control input for the BCK/UP LAMPS PCB RELAY as coming from the BCM.
  8. Conlan Rose

    Conlan Rose Epic Member 5+ Years 1000 Posts

    Can you take a picture of the relay so we can visualize it and how it is installed. It should be removable even though GM does stupid thinks like non replaceable lamps in the dash and what not there's no way they would make a relay non removable.
  9. Alan Crosby

    Alan Crosby Member

    fuses underhood 2007 burban.jpg
    I don't know if this image will be visible or not, but it is an image that I found that matches the layout of the fuses and relays that are visible on the top of the fuse block. There isn't one that says BCK/UP LAMPS PCB RELAY. The key is PCB - printed circuit board. The relay I was sold is the same as the PRK LAMP and a few others. I tried replacing it with all of the ones of the same type. When I found a listing of all the fuses and relays in the underhood junction block, there was a section like the list above, plus another list of relays that were not serviceable. It was in this second list that I found BCK/UP LAMPS PCB RELAY.

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