No backup lights, fuse/bulbs ok

[sbagdon]

This is for a 2000 Silhouette, yet I see there's lots more traffic for the Venture, so thought I'd start here first.

Backup lights don't light, when minivan put into reverse. b/up fuse ok (engine bay, #27), bulbs ok (swapped with new lights, and switched with turn lights, to confirm).

The circuit board is a potential, yet hard to believe that out of 8 bulbs, only 2 would go, and that would be 1 on each side, and only the reverse lights (not the marker, stop, or turn). Will go at it with a multi-meter, to see if there's current, for the next step.

Searches show that it could be the gear position sensor, stuck with what part this would be, and where this part would be. Would this be a pin-to-ground physical sensor, a gear position sensor by the transmission, something linked to the gear selector arm, etc? And once found, is this something that is replaced, or adjusted (imagine the reverse lights going on, when in neutral!)? Still looking for info, on that one.

Input welcome.

Thanks!

[lesterl]

Check the harness going to the tail lights, speciffically where the wires go thru the floor board......

[merc81]

Absolutely check the pass-thru connector. And even if it looks impossible, those wires in the light assemblies--at the connectors--are almost always bad. Use a test light, don't use a frame ground either--use the ground on the harness.
I'd bet its right at that connector on the tail light.

[sbagdon]

Originally Posted by merc81

Absolutely check the pass-thru connector. And even if it looks impossible, those wires in the light assemblies--at the connectors--are almost always bad. Use a test light, don't use a frame ground either--use the ground on the harness.
I'd bet its right at that connector on the tail light.

The improbability is that out of 8 lights, only those 2 would go bad, and with that 1 on each side, just for those lights. Yet I agree, it needs to be checked, just running into a time issue right now, it's next on the maintenance/repair task list.

Holding off to order the factory service manuals (cost), so here's a question:

If I block off the wheels and put the vehicle into reverse, then pull the b/up fuse (engine bay, #27), I should find 12v on one side of the fuse plug, correct? I'm guessing that no 12v at the b/up fuse means relay, while 12v at the b/up fuse means continuity issues between the fuse and the bulb (harness, circuit board, etc). That would at least tell me what direction to take, in the wiring harness.

Is that logic correct?

[lesterl]

My logic at this time isnt the best, but it sounds reasonable to expect that. BTW you dont need the engine running, just ignition on and in reverse.... Could be a bad mode switch also.

[sbagdon]

Originally Posted by lesterl

My logic at this time isnt the best, but it sounds reasonable to expect that. BTW you dont need the engine running, just ignition on and in reverse.... Could be a bad mode switch also.

Makes sense, on the engine not needing to be running, thanks.

Yet where is the mode switch? Is it a mechanical switch on the transmissions, or an electro-mechanical on the shifter assembly? Thanks!

[merc81]

Originally Posted by sbagdon

Makes sense, on the engine not needing to be running, thanks.

Yet where is the mode switch? Is it a mechanical switch on the transmissions, or an electro-mechanical on the shifter assembly? Thanks!

I don't have my shop manuals here in the office, but I can tell you from experience there are no devices other than the switch on the tranny linkage that could do it. There is a switch box that saddles the input shaft of the linkage on the transmission housing. This would have to be the switch. Its easy to get to, once you remove the intake hoses and MAF sensor.

[lesterl]

Should be a black plastic housing that sits over the selector shaft on the transmission, it is about 3"X3" or so IIRC. Yeah, real easy to spot when you get the intake duct off etc.......

[sbagdon]

Originally Posted by lesterl

Should be a black plastic housing that sits over the selector shaft on the transmission, it is about 3"X3" or so IIRC. Yeah, real easy to spot when you get the intake duct off etc.......

I'll look for it this weekend, thanks.

Any idea how to diagnose it? Is it a ground pin to a relay, or 12v passthrough?

And yes, I really need to find the manual with wiring diagram... just can't afford the full factory set, for a week or two. So thanks for all the ideas, until then!

[merc81]

I have it at home, but I don't have internet at home...
I used to keep it here in the office until recently I had to use the books for a repair problem.
If you still need them on Monday, I'll scan the diagram in then.

[sbagdon]

Originally Posted by merc81

I have it at home, but I don't have internet at home...
I used to keep it here in the office until recently I had to use the books for a repair problem.
If you still need them on Monday, I'll scan the diagram in then.

Thanks, pm for contact info.

Tested the b/up fuse using a test-light, it has power all the time. Fuse must be between the power-source and switching device. Backfed power through the light circuit board (by accident, trying to test-light it), the lights on both sides work if you put power to the back of the circuit. So it's between the fuse, and the rear of the car.

Really suspecting it's the reverse switch, presumably on the top of the transmission. I was able to see the gear selector sensor box on the top of the trans, without removing the air intake parts (has the shift cable, and a few harness connections?). Figure it makes sense if it's bad, yet don't want to do anything until I have the factory manual test procedures. If anyone has the short-version (memory, or manual), please feel free to share them!

[lesterl]

Sounds like the switch is real suspect at this time, need to probe the terminals and see if you have power going in and not out. (might have someone watch the lights as you run the shifter thru the gears from park to low.....)

[sbagdon]

Originally Posted by lesterl

Sounds like the switch is real suspect at this time, need to probe the terminals and see if you have power going in and not out. (might have someone watch the lights as you run the shifter thru the gears from park to low.....)

Thanks for the ideas! Just checked, no reverse lights in any gear (in case it was misaligned), can't speak for between gears (that would be funny... b/up lights only going on in "2"!).

Just going to have to wait until I find the official debug test steps. Unless I can get to the box by going through the left/front wheel-well trim, the intake and coolant bottle has to come out, and that'd be a pita. Would have to take it all apart to test, then put it all back together while waiting to find the part. And not going to order that part without absolute test procedures completed, as I suspect this is not a cheap part from GM!

[sbagdon]

With the generosity of a fellow member, I now have a copy of the wiring harness pdf. It's about what I expected, this should give me the info I need to test the transaxle range switch this coming week. The circuit appears very simple, so this should get me through the next step.

edit: Also, digging through the psd manual, it appears the transaxle range switch is part of the psd logic (won't open if not in park, etc), and if the trs is hosed, the psd diag won't work at all. This one part is starting to be a pita...

[sbagdon]

Can get the part from a remote dealership via mail order, comes out to about $65 (not sure about taxes/shipping), so about $80ai? So it's really a "cheap" part after all (yes, after some other parts, my bar is set high for "cheap"!). If you've made it this long in the thread... is it worth just ordering and replacing, or wait before confirm testing of the part?

As the b/up fuse is ok, and the lights and circuit board is ok, and the psd is hosed, aside from a wiring harness break just for this circuit between the front and back (and the psd being hosed for another reason), it really appears to be this part. And I don't feel like taking the intake plumbing off more then once. Thoughts?