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Reverse light woes with the Caddy

Russell

Russell

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As most of you know, I've got a 2003 Cadillac Escalade that I have turned into something of an offroad toy. I've swapped out the IFS for a D60 solid front axle and the 10 bolt out with a full float 14 bolt, 3 link suspension front / rear with king coilovers and air bumps. I removed the LQ9 6.0L/4l65e/AWD t-case and installed a replacement 2005 LLY Duramax diesel engine with a ZF6 six speed manual transmission and a 29 spline NP241 manual transfer case. I am very familiar with swapping these engines around, my last build was a 95 Chevy Tahoe with an 02 LB7 Duramax / ZF6 combo. After some effort involving ripping the entire dash out and re-working the entire I/P harness to convert it to manual, relocating the Bose amp to the rear quarter panel above the spare tire tools to allow for a jump seat and installing the pedals I wound up with an install that you could more or less take to GM and have them service it. The dash has no warning lights on at all and everything works right down to the VATS system.

Except for my reverse lights. I am totally stumped.

Using my Tech 2, I can see that both the ECM and the BCM report the manual trans rev switch as ON when I put the trans into reverse, and OFF when I take it out again. I've verified that there is 12V at the BCM and at the ECM input pins with the transmission in reverse. I've also verified that the TBC-B fuse in the I/P fuse block is good (my dome light works fine). I also checked all the other battery, IGN 1, 2 and 3 inputs to the BCM along with all the grounds. When I unlock the truck with my remote and the perimeter lighting is on, the reverse lights turn on. I can also turn the reverse lights on manually with the Tech 2 and they work just fine. The only thing I can see wrong with the Tech 2 is that the Reverse light call PID remains INACTIVE when I put the transmission into reverse.

I was having some issues with the BCM not sending out the power master mode commands properly which was causing a battery drain. I figured perhaps the BCM had a fault internally which was causing it not to turn the reverse lights on. I installed a replacement BCM and programmed it using TIS2WEB tonight. This fixed the battery draw and got the PMM stuff working properly again, but the reverse lights still don't work.

I should mention that the lights worked fine with the auto trans before I started the swap.

Does anyone know if perhaps the BCM is waiting for a status flag from the PCM before it will turn the reverse lights on? Is there any other conditions that need to be met to turn them on outside of the key being in RUN and the transmission in reverse?

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This is all gm says about it. From what I can tell it seems like you have everything. Have you tried with the engine running? I’ve seen that on some vehicles where they only work if the engine is running.
 
Ah, so the PCM is failing to request the reverse lamps. Relay it is, I guess!

Also had the air bag light pop up today. I guess the BCM and SDM didn't pair properly when I installed it. no option to learn the keys from the tech 2. Not sure what else I can do now?
 
I think I know what is wrong with the SDM, I didn't do a VTD relearn after I replaced the BCM since the truck still starts okay. I tried to do a tis2web 10min relearn today to set the restraint codes in the BCM but was unable to as I kept getting an error (35 and 36). I called techline and they suggested that a key is wrong somewhere on the serial bus.

I suspect it may be the Duramax PCM to blame. I am going to disconnect it and temporarily hook up a stock LS PCM and see if I can run the 10 min relearn then. If all goes Well I can hook the dmax PCM back up and force it to learn the codes with EFILive as I did the first time around.

Hopefully that does the trick. I will hold off installing the reverse light relay just in case this stuff fixes them in the process haha!
 
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Stuff definitely gets screwy when changing things around like this. I think its awesome you have it all working together so well
 
Can you post pictures of the interior? I’d love to see how that looks with your mods! I love diesel swaps!
 
Taken from the 2003 Silverado manual in SI:

Backup lamps- manual transmission

The B/U LP 20A fuse in the underhood fuse block supplies battery positive voltage to the normally open backup lamp switch. When the driver places the gear selector lever in the reverse position, the switch closes and the voltage is from the swtich to the body contol module (bcm). The bcm supplies voltage on the backup lamp supply voltage circuit to the backup lamps and the automatic day/night mirror. Voltage for the courtesy lamp supply voltage circuit and backup lamp supply voltage circuit is from the TBC B fuse in the instrument panel fuse block directly through the bcm to these circuits. A short to gound on either of these circuits will open the fuse .The backup lamps are grounded at G401.

Looking at both schematics for a Silverado and an Escalade, all you should need to do is put power with the shifter in reverse to terminal A8 on connector C4 at the body control module. It's the same terminal location for either vehicle. Put power there and the backup lights should come on as normal.
 
Yep, I found the same info. I also do have 12V at the BCM C4 A8 connector pin in reverse. The BCM even changes the man trans rev switch tag to ON when I put it into reverse. I guess the LS PCM and the diesel PCM must send the reverse request as a different bit over the serial network.

my plan is to install a relay with the reverse lights hooked up to common, the BCM output connected to the normally closed and my own ignition power supply on the normally open. The coil will turn on with the voltage from the switch (which will continue to feed the PCM and the BCM). This means the BCM can still turn the reverse lights on with the perimeter lighting, but the reverse switch will power the lights and the backup assist module without feeding back into the BCM.

Hopefully the BCM doesn't complain too much when it has no resistance on the output when in reverse.
 
The idea to run a relay is smart. But, looking at the schematic the pcm does not have any impact on the lighting circuit for the manual trans setup. The schematic posted earlier is almost the same as the one for an 03 Silverado except it only shows the pnp switch only. The truck schematic shows both the pnp and the backup lamp switch for the manual.

Just went back to re-read the automatic transmission description and operation. You are right, the BCM is looking for a class 2 message that the trans is in reverse. So even with power at the terminal I noted it won't turn on the lights without the class 2 message.

I don't think the relay will freak out the BCM the way you intend to wire it up.
 
No more airbag light!

I wired up a spare LS PCM I had on the shelf (those wires are just pushed in, no terminals haha), removed the LLY PCM, hooked the LS PCM up, set the VIN to match with EFILive, then flashed the stock programming in with TIS2WEB. When I tried to "start" the truck, the VTD system kicked in. With the security light on I was able to run the 10min VTD relearn with TIS2WEB. After 10 min was up I tried to "start" the truck again and everything all paired together. Noticed right away that the air bag light was off though!

Next I removed the temporary LS PCM and put the LLY PCM back in. 5 minutes with EFILive and it had learned the new security codes and voila, she runs again!

Still no reverse lights though, d'oh!!

I will pick up a relay for my idea tonight and hopefully will have time on Tuesday or Wednesday night to install it before we head for the mountains to go wheeling!

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I really appreciate the RPM redline being adjusted for the diesel :bow:​
 
That is actually the cluster from the diesel donor. I sent it away to get the VIN changed to match the Escalade and had the mileage set to match the original cluster (they were within 10k of each other, but I wanted to keep it legit). I had the speedo shop enable the steering wheel controls as well. I added the Escalade bezel and white dials, upgraded all the stepper motors and put a new clear plastic face on.

It almost looks stock to the Caddy, but a sharp eye will noticed the dial faces are from the truck vs the escalade.

I also need to re-solder one of the resistors to fix the LED display as it is super dim and cannot be seen in daylight.
 
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