Factory LED Both Rear Turn Signal Lamp Outage

[Mitch_308]

Been searching for this topic for a couple days and didn’t see a relevant thread to my situation so I’m putting it out there for the Ram guru’s to lend a helpful hand. 2022 Ram Sport with factory LED tails. Truck is still under warranty (30,000 km) but last time I went in for an annoying suspension creaking noise, they said it was the brakes and I needed to pay $174 CAD for a lube job so I’m hesitant to go back for.

I recently took the negative off my battery for a couple hours to take my telematics module out so I can have the performance and off-road pages work without them being deleted. Since putting the negative back on, I’ve been getting rear left and right turn signal lamp outages even though all lights are visually verified to be working and activating at the normal speed. Inside I get the fast flash and the message pop up. With the side mirrors folded in they start blinking slow then the error message pops up and they fast flash.

Interesting thing I found after a couple days driving is that the message goes away and isn’t in stored messages once I turn the lever off. I can then put the turn signal that was just “out” on until the cows come home and it won’t say it’s out or fast flash. But, if I was braking and then put the turn signal on then after 10 flashes or so it will come up with the turn signal outage.

My thoughts from searching other threads are that the 3rd brake light bulb could be on its way out and triggering it, which kind of makes sense since it’s only during braking but at the same time doesn’t make sense as to why the message displays turn signal faults. The brake light still works and I will swap bulbs out for new ones to see but I didn’t have time this week/weekend to verify.

So tldr, turn signal outage message comes up but flash like normal. Took the negative off the battery before this and now am having this issue pop up. I believe the third brake light might be the issue but I would like others’ opinions on what it might be.

 

[Mitch_308]

I tried swapping the third brake light bulb and it didn’t fix it. Got alfaobd out with my scanner and I’m getting two faults. B1642 and B1646 (Short circuit to + battery/open circuit) for which I’m assuming that’s left and right rear taillights.

 

[6of36]

I tried swapping the third brake light bulb and it didn’t fix it. Got alfaobd out with my scanner and I’m getting two faults. B1642 and B1646 (Short circuit to + battery/open circuit) for which I’m assuming that’s left and right rear taillights.

It also says open ground. Check those. There are 30 ground points on a Ram1500.

 

[Mitch_308]

It also says open ground. Check those. There are 30 ground points on a Ram1500.

I went out this morning to see if it magically fixed itself overnight and the message pops up immediately without turning the truck on now. Before it was just brake applications with the turns on and now it’s whenever the truck is on. Slow flash outside still and can’t see any LED’s out but inside and mirror lights flash fast.

I was able to get an appointment in a couple days to get them looked at by the dealer so I’ll put it in their hands until they either fix it or deny warranty and then I’ll start to tinker with it.

Didn’t have an issue until I took the negative off the battery so I hope I didn’t fry anything inside the taillights when it reconnected. If it is a simple ground issue, how would it not present an issue until after reconnecting the battery? Not trying to sound arrogant at all, just want to understand the issue better.

 

[6of36]

I went out this morning to see if it magically fixed itself overnight and the message pops up immediately without turning the truck on now. Before it was just brake applications with the turns on and now it’s whenever the truck is on. Slow flash outside still and can’t see any LED’s out but inside and mirror lights flash fast.

I was able to get an appointment in a couple days to get them looked at by the dealer so I’ll put it in their hands until they either fix it or deny warranty and then I’ll start to tinker with it.

Didn’t have an issue until I took the negative off the battery so I hope I didn’t fry anything inside the taillights when it reconnected. If it is a simple ground issue, how would it not present an issue until after reconnecting the battery? Not trying to sound arrogant at all, just want to understand the issue better.

These trucks have so much electronics on them that anything can cause issues. When I looked up the codes you listed, open ground came up too. Could be that the ground was poor, but still making, until juice stopped flowing through, and is now lost. I have seen weirder problems posted on the forum, caused by grounds. I've seen installing aftermarket LED bulbs cause problems. You definitely may have a different problem, but most problems I read about on here, are batteries, and grounds.

 

[Mitch_308]

These trucks have so much electronics on them that anything can cause issues. When I looked up the codes you listed, open ground came up too. Could be that the ground was poor, but still making, until juice stopped flowing through, and is now lost. I have seen weirder problems posted on the forum, caused by grounds. I've seen installing aftermarket LED bulbs cause problems. You definitely may have a different problem, but most problems I read about on here, are batteries, and grounds.

Ok that makes sense. I hope that’s all it is and I appreciate your input.

 

[Mitch_308]

Took it into the dealer today and they didn’t have enough time to trace the short in the wiring. Bringing it in next week to leave with them for a day. Said it was the fault sense circuit though.

That being said, does anyone know where the fault sense wires are in the taillight harness/colour/pin location?

 

[Roman2179]

Here are the pinouts. The harness follows the left frame rail to a connector that goes through the drivers footwell.

 

[6of36]

Damn! 4 grounds for each light, that's crazy.

 

[Mitch_308]

Here are the pinouts. The harness follows the left frame rail to a connector that goes through the drivers footwell.

Thank you for the pinouts! Is there a certain voltage I should be looking for on the fault sense circuit?

Also thanks for the info on the location for the harness. Where did you find the diagrams?

 

[kapinallinen2]

Both of then should not start acting up simultaneously.
Did you try re-installing the telematics module to see if the problem went away?

 

[Mitch_308]

Both of then should not start acting up simultaneously.
Did you try re-installing the telematics module to see if the problem went away?


View attachment 170102 View attachment 170103

If the dealer comes up empty handed again I’ll consider putting the module back in.

I took the negative off once before for maybe 30 mins to install the factory brake controller with no issues reconnecting but to take the telematics out it was probably 2.5 hours from start to finish. My train of thought is it was either a surge upon reconnecting that started the issue or maybe a ground was barely hanging on and finally let go. Looking under the truck it’s pretty dirty from undercoating last year and maybe some oil or dirt seeped between the connection. It was also raining quite a bit the past couple of weeks so maybe moisture in a connector too?

My previous 19 Ram classic needed dialectic grease in the tailgate connector every spring/fall to get the backup camera working reliably for what it’s worth.

Where were you able to get the wiring diagrams and troubleshooting sheet? It’s really informative and I appreciate you reaching out to help!

 

[kapinallinen2]

If the dealer comes up empty handed again I’ll consider putting the module back in.

I took the negative off once before for maybe 30 mins to install the factory brake controller with no issues reconnecting but to take the telematics out it was probably 2.5 hours from start to finish. My train of thought is it was either a surge upon reconnecting that started the issue or maybe a ground was barely hanging on and finally let go. Looking under the truck it’s pretty dirty from undercoating last year and maybe some oil or dirt seeped between the connection. It was also raining quite a bit the past couple of weeks so maybe moisture in a connector too?

My previous 19 Ram classic needed dialectic grease in the tailgate connector every spring/fall to get the backup camera working reliably for what it’s worth.

Where were you able to get the wiring diagrams and troubleshooting sheet? It’s really informative and I appreciate you reaching out to help!

The BCM could be going bonkers trying to poll the telematicks module and not getting a response therefore throwing a false turn signal fault, just my WAG.

As far as the service manuals go. I have been subscribing to Alldatadiy for the last 10 years or so for different vehicles. Well worth the 56 bucks a year IMO.
Do It Yourself Automotive Repair Information | ALLDATA DIY

 

[Roman2179]

The fault sense circuit is pretty simple. Basically whenever the turn signals flashes, it pulls the fault sense line to ground. Not sure what voltage you're going to see on it but I wouldn't expect it to be very high.

Both going out at the same time is also extremely unlikely. Are you sure you didn't disturb the BCM wiring while pulling the TBM? Both fault sense wires for the rear tails are on the C6 connector on the BCM. Retrace your steps and make sure you didn't unplug / fully seat a connector.

 

[Mitch_308]

The BCM could be going bonkers trying to poll the telematicks module and not getting a response therefore throwing a false turn signal fault, just my WAG.

As far as the service manuals go. I have been subscribing to Alldatadiy for the last 10 years or so for different vehicles. Well worth the 56 bucks a year IMO.
Do It Yourself Automotive Repair Information | ALLDATA DIY

I used alfaobd to disable the telematics module in addition to physically taking it out. Haven’t got any errors on the uconnect screen so I don’t think it’s looking for it anymore.

I’ll have to look into using the site and saving all the relevant pages.

 

[Mitch_308]

The fault sense circuit is pretty simple. Basically whenever the turn signals flashes, it pulls the fault sense line to ground. Not sure what voltage you're going to see on it but I wouldn't expect it to be very high.

Both going out at the same time is also extremely unlikely. Are you sure you didn't disturb the BCM wiring while pulling the TBM? Both fault sense wires for the rear tails are on the C6 connector on the BCM. Retrace your steps and make sure you didn't unplug / fully seat a connector.

I’ll give the connector a look and give them a gentle push to make sure it’s connected fully.

Truck is going in on Wednesday to the dealer so hopefully I’ll have a successful outcome and solution to share.

 

[Mitch_308]

Got the truck back. Having the issue still after I just about got home. Work order said they load tested grounds and they were ok. Found resistance was high on both circuits and found pinched/corroded wires in the rear harness at the frame rail. Repaired and no codes but the turn signals still said they were out within 10 flashes with my foot on the brake. Taking it back in tomorrow.

 

[Mitch_308]

Pulled two new codes. B1793 and B1792. Both short circuit to ground and it also says “error intermittent” in the description.

 

[kapinallinen2]

Pulled two new codes. B1793 and B1792. Both short circuit to ground and it also says “error intermittent” in the description.

So both sides are still faulting, the joy...

 

[Mitch_308]

So both sides are still faulting, the joy...
View attachment 170336 View attachment 170336

If it was the BCM would it not make other things go crazy as well? Hoping that maybe digging more into that harness they’ll find something else pinched or corroded.

Hopefully better news tomorrow. Worse case scenario, could I turn off the rear lamp outage in alfaobd without causing any big issues if they can’t fix it?