Hey all, currently troubleshooting a new issue, could use a hand with some next steps. Car is an '04 C5, auto, ~160k on the clock

Reverse lights do not work when the car is in reverse.
If I lock the car, the reverse lights flash as expected, and if I unlock the car, the reverse lights come on as expected and shut off after 30 seconds or so. So the bulbs work and are getting power from that circuit. For some reason, they just aren't getting power from actually being in reverse gear.
With key on engine off, I am only getting code B2482 - "Backup Lamp Relay Circuit"

- I checked fuse #21 in the passenger footwell, it looked fine. Replaced with another working fuse, still no reverse lights.
- I checked fuse #2 in the engine fuse box (DRL/backup lamps), and it is good as well. DRLs are also working just fine.
- I checked relay #38 in the engine fuse box. Visually it looks fine, I popped the cover off and it looks okay. I can feel it click when I unlock the car and the reverse lights come on.
- I then tried jumping pins 30 and 87a for this relay slot with a piece of wire, however still no lights when I put the car in reverse. Note: I am testing this with key on, engine off. I would assume the reverse lights would still come on like this, and the engine wouldn't need to be running, however I could be mistaken so let me know if I'm wrong. I also could be testing the wrong pins, or just testing it wrong altogether - I'm not the greatest with electrical troubleshooting, just going off of a prior post I found from searching.

Any other suggestions? I'm thinking if the bulbs are fine, the fuses are fine, and the relay is fine, then perhaps it's the neutral safety switch? I've done some searching of old posts and 99% of them end up being either a bad fuse or the reverse switch on the side of a manual trans, but mine does not have this switch since it's an auto. I haven't been able to find any solutions for an auto trans, most of them sadly just end up being dead threads with no solution shared.

Thanks in advance!

 

Hey Kev !!…what’s happening ??….no reverse lights huh ??…remove relay 38 and if you have a test light connect it to ground…probe the middle pin of the 3 pins that are together…that is pin 87A…turn the key on and put the car in reverse…the test light should light…if not you will have to check your PNP switch which is on the left side of the tranny…should be a gray and brown wire…you can try jumping across the switch and see if the test light now lights. !!..BTW pins 87 and 86 should be hot at all times…key off !!

 

Thanks for the quick reply! I gave that a test tonight and my test light did not turn on when probing the slot for pin 87a. Just to make sure my test light was working, I tested the slots for pins 86 and 87 as well and it DID light up for those. So it seems like perhaps the PNP switch may be the culprit.

Next up I'll back the car onto ramps and see if I can locate the switch underneath and test the harness for that, but it probably won't be for a couple days. I did new u-joints and a rear axle seal on my 3rd gen 4Runner this weekend and I'm still quite sore from that, last thing I want to do is crawl back under another vehicle lol.

I'll post back with results soon! Assuming the harness tests out good which would mean the switch itself is bad, I'm hoping it's not too difficult of a job to replace.

 

Great !!…let us know what you find…PNP switch shouldn’t be to bad but first try jumping it to be certain !!

 

So I got underneath today, and this is the only plug I could find on the drivers side of the transmission. I’m hoping this is the correct one however, I can’t tell which pin is the one I need to test. Any advice?

 

Do you see brown and gray wires ??

 

Let me see if I can pull the loom apart a bit. Am I looking for one that’s brown & gray striped or one brown, one gray?

If separate wires, I’m guessing I test across both of them?

 

Wiring diagram I sent only shows a brown and gray…did you look at it ??

 

I’m not the greatest with electrical diagrams but I see what you mean now.

I was able to get the harness exposed a little more, it looks like there’s possibly two gray wires. On one side there’s a gray and a brown right next to each other as seen in the first pic. But if I flip the harness over, it appears there’s another grey one.




When testing, I should have the key on and the car in reverse, should the harness be plugged in and I backprobe the wires? Or is it fine to just test while it is unplugged?

 

What you can do is get your ohm meter and see if you have continuity between terminals C and F on the switch (if it’s lettered ) itself when you go from park to reverse….don’t know what the other wires go to on that harness…must be part of the back up lamp circuit !!..#1 is the PNP !!

 

Thanks again for the help. Unfortunately after another look I didn’t see any C or F markings on the switch or the harness. It seems like the PNP switch on my trans is slightly different than the one in the diagram above. Mine has one large plug while that one has two smaller plugs.

I tried jumping the brown and gray terminals that were next to each other (in the first picture above) which were numbered 10 and 11, but didn’t have any luck. Although, I’m wondering if the fact that the entire harness is unplugged may inhibit the results? Regardless, I ran out of time & daylight tonight to continue troubleshooting so I’ll try again later.


Is this no reverse light situation a somewhat common issue with auto PNP switches? If so, I may just try to get a new one and swap it out since everything else seems okay. Seems like I may be able to get to it just by removing some of the exhaust that’s in the way.

 

You should ohm out the 2 terminals on the switch side and NOT on the harness side…don’t know if that’s what you did !!…figure out where the 2 wires are on the switch (if there are 2 grays try each one) and connect the ohm meter to those 2…put the car in reverse and see if you have continuity between those 2…if you have continuity the switch is good so further troubleshooting is required !!…I’ll look tomorrow for the switch pin out…could not find it anywhere !!…the pic is from my 01.

 

Ahh, understood. I will try that next. I was using a test light across the terminals on the harness with the car in reverse. I’ll see if I can determine which pins on the switch are for which wires and then check them for continuity. It’s a pretty tight squeeze so I’ll likely need to drop the over axle exhaust just to be able to reach it.

 

Yes !!…just checking for continuity on the switch when you’re in reverse..you can also check with your test light the brown wire on the harness with the key in run as per the wiring diagram…it should light up…is fuse 21 good ??

 

Fuse 21 is good. I checked it again today. For the test light, brown wire to ground or brown wire to gray wire?

 

Test light connected to ground and then probe the brown wire on the connector in run. Test light should light or you can use your voltmeter and see if you have 12 volts there.

 

Got it, thank you!! Electrical troubleshooting is NOT my forte if you couldn't tell lol. I will check this again soon.

 

Update: got back under the car today and did the following:

- Test light from ground to brown wire in harness with car in reverse, did not light
- Tested the two corresponding pins (brown & grey wires) on the switch itself, in reverse, no continuity. On the contrary, if you look at the first picture I uploaded, I tested across the furthest left and right pins and they DID have continuity. These appear to be for the purple & light green wires.
- Since I was going to be under the car anyway, I went ahead and just ordered a new PNP switch just to put on regardless, and get it all done in one go. Was a fairly easy replacement, however - still no reverse lights.
- After finishing these tests, I double checked fuses 2 (engine bay) and 21 (passenger footwell), and also replaced mini relay 38 in the engine bay with one of the DRL mini relays. Still no dice. Lights still work when locking/unlocking with the fob, just not in reverse.

With that being done, I'm guessing the next step may be a short in the harness somewhere? If so, how/where should I begin troubleshooting this? Bummer that a new switch didn't solve the issue, however this was fairly cheap preventative maintenance anyway. Original switch was ~160k, now I know this new one won't fail and leave me stranded in the near future.

Lastly -- since the last big fix you helped me on a couple years ago was seemingly the crank sensor, but ended up being a bad cam sensor that was on the same circuit, is there anything else shared across this circuit? Perhaps something else that could be shorting or going bad that's causing the reverse lights to not work?

 

Even though you put in a new PNP switch did you put it in reverse and make sure you have continuity??…don’t assume it’s good !!