SOLVED! DDM, PDM and keyless entry fob not working after a work done on the truck

[ghost_leader07]

Hi everyone and sorry for the long post in advance.

I'm doing a few mods and upgrades on 2004 Chevrolet Trailblazer LT the latest was sound deadening the whole car which had me to remove almost everything on the floor seat, carpet and the fuse box/ECM, everything was disconnected for a while (few months) after I was done with sound deadening and carpet upholstery i started reassembling the fuse box and the shifter assembly (just note i have all the door panels removed including the DDM and PDM and both rear window switches for LED mod as well)



Since the car was parked for a couple of months i decided to start it up just check to everything is good (keep in mind i didn't plug any of door switches at this point) truck started up fine. But i did notice when i turned it off and remove the key the doors or something started locking or unlocking multiple times before it stops, it happened each time i start and turn off the truck but it no longer does that now, i plugged all the switches and both driver and passenger switches i have no power in both completely dead, rear window switches are working. Also my keyless fob is not working and the battery is good. If you open the tail gate and close it i can hear something like a latch engages but the tailgate is not locked.



I made sure all of the plugs at the rear fuse box is connected well and tested all of the fuses and all are good however i found 10A of DDM was blown but the cheap@$$ previous owner did the unthinkable and hardwired the blown feuse with a thin cooper strand!! I'm afraid it did some damage to the DDM but that doesn't explain why the PDM is not working on both sides as well when testing alongside the keyless fob i believe these are related but my knowledge is quite limited.



I would really appreciate any help or guidance on this matter.

A.

 

[ghost_leader07]

Note:
I forgot to mention my rear wiper and washer also not working, all of these were working before the disassembly.

 

[TollKeeper]

So the CANBUS is likely not able to work because the DDM/PDM are not connected for the reference signal to the receiver module in the trunk area. With the rear wipers not working, is also a point in the grounds not being present in the rear section of the truck. Start with grounds (ALWAYS) and see what you get.

 

[ghost_leader07]

So the CANBUS is likely not able to work because the DDM/PDM are not connected for the reference signal to the receiver module in the trunk area. With the rear wipers not working, is also a point in the grounds not being present in the rear section of the truck. Start with grounds (ALWAYS) and see what you get.

Where are the grounds at the rear? Is it near the fuse box beneath the seat or in the tailgate?

 

[TollKeeper]

Im not sure to be honest, It has been discussed in the forum previously. If I am remembering correctly, in the rear quater panel on the drivers side

 

[ghost_leader07]

Im not sure to be honest, It has been discussed in the forum previously. If I am remembering correctly, in the rear quater panel on the drivers side

Okay I'll check for ground connections and make sure everything is good.

I've a few questions, is the tailgate control module responsible for the the DDM, PDM, keyless fob and rear wiper/washer? Since everything was working before pulling stuff out is it possible it got shorted for whatever reason? And how do you go about testing the tailgate module and rear fuse box for issues?

 

[Blckshdw]

The images in this thread should help.

Electrical Ground locations

While troubleshooting a bad ground I came across some scans of the service manual regarding electrical ground locations for our platform posted on another site. This includes both short and long wheel base, as well as both 4.2L and 5.3L. Credit goes to Wex...

gmtnation.com

 

[ghost_leader07]

The images in this thread should help.

Electrical Ground locations

While troubleshooting a bad ground I came across some scans of the service manual regarding electrical ground locations for our platform posted on another site. This includes both short and long wheel base, as well as both 4.2L and 5.3L. Credit goes to Wex...

gmtnation.com

Thank you. I'll check for those grounds, and let you know what i come up with.

 

[TJBaker57]

I've a few questions, is the tailgate control module responsible for the the DDM, PDM, keyless fob and rear wiper/washer?

No, the LGM (liftgate module) is not "responsible" for, or dependent on the DDM or PDM.

The LGM is responsible for the rear wiper, keyfobs, TPMS if equipped and liftgate locks etc. ALL of these actions are dependent on the Class II serial data bus. (no ISO 15765-4 CANBUS there). No communications, nothing functions.

There is a splice pack under the rear seat in the right side under the carpet. This is where the single wire Class II communications from all of the modules in the rearward portion of the truck tie together before going to going the rest of the network at the front splice pack. The DDM, PDM, LGM, VCIM, AMP (if equipped) etc. are the modules that tie to that rear "hub".

Might you have disturbed any communications wires? They look exactly like any other wire.

 

[TollKeeper]

I thought the LGM was interfaced with the FOB module?

 

[ghost_leader07]

No, the LGM (liftgate module) is not "responsible" for, or dependent on the DDM or PDM.

The LGM is responsible for the rear wiper, keyfobs, TPMS if equipped and liftgate locks etc. ALL of these actions are dependent on the Class II serial data bus. (no ISO 15765-4 CANBUS there). No communications, nothing functions.

There is a splice pack under the rear seat in the right side under the carpet. This is where the single wire Class II communications from all of the modules in the rearward portion of the truck tie together before going to going the rest of the network at the front splice pack. The DDM, PDM, LGM, VCIM, AMP (if equipped) etc. are the modules that tie to that rear "hub".

Might you have disturbed any communications wires? They look exactly like any other wire.

Thank you for your detailed response, i don't believe i have distributed any communications wires but I'll to try lift the carpet to check the wires you mentioned.

 

[TJBaker57]

Thank you for your detailed response, i don't believe i have distributed any communications wires but I'll to try lift the carpet to check the wires you mentioned.

You will see a slit in the carpet under the right side. No need to 'lift' carpet you can access the pack for a look easy enough.

 

[TJBaker57]

Maybe try the liftgate functions (keyfobs, rear wiper) without the DDM and PDM connected first?

Do you have a scantool or even a bluetooth OBD2 dongle?

 

[ghost_leader07]

You will see a slit in the carpet under the right side. No need to 'lift' carpet you can access the pack for a look easy enough.

This correct? What should i look for?

 

[ghost_leader07]

Maybe try the liftgate functions (keyfobs, rear wiper) without the DDM and PDM connected first?

Keyfobs and rear wiper/washer are not working. Are you familiar with the unlocking noise i mentioned in my OP? It felt like the locking system was trying to recalibrate but i didn't plug the DDM or PDM at the time (my truck is almost completely stripped apart from the dash) it happened after i turn off the truck and remove the key but it doesn't happen any more.

Do you have a scantool or even a bluetooth OBD2 dongle?

No. Unfortunately i have a cheap odb2 scanner but it won't connect to the truck but i used a more advance scanner for a friend of mine and it connected no problem. I'm going to order one tomorrow but it'll take awhile to arrive.

 

[TJBaker57]

This correct? What should i look for?

just make sure all the wires are good. the light blue (2002 model year) is the one from the liftgate module. There should be a dark blue with white stripe (2002 model year) that goes to the underside of the left dash where it joins another splice pack that ties all the rest of the network together.

 

[TJBaker57]

I'm going to order one tomorrow but it'll take awhile to arrive.

It is worth having one of these inexpensive bluetooth dongles. They won't do the work for you but we can show you how to check a lot of things with them, even stuff the expensive scantools cannot do.

https://www.amazon.com/dp/B011NSX27A/?tag=gmtnation-20

 

[TJBaker57]

Keyfobs and rear wiper/washer are not working

There are of course other things that could be the trouble there. The wires inside the rubber boot between the body and the liftgate can break inside the insulation and look fine from the outside. The fact that you hear a latching when you close the liftgate suggests that the power amd grounds for at least some of the liftgate are OK though. But the communications line could be broken.

When the drivers door module and passenger door module are disconnected it is important to isolate the harnesses that are not connected of course. Leave no chance for anything there to ground out.

I am still wondering what caused the sound you previously heard when shutting off the truck and removing the key. Haven't come up with a plausible explanation though.

 

[Blckshdw]

If you open the tail gate and close it i can hear something like a latch engages but the tailgate is not locked.

This part, is normal. The repeated locking and unlocking of the passenger doors, is not.

 

[TJBaker57]

But i did notice when i turned it off and remove the key the doors or something started locking or unlocking multiple times before it stops, it happened each time i start and turn off the truck but it no longer does that now,

The presence of the key is only known to the BCM under the rear seat by the fuseblock there. The BCM is wired directly to the 2 rear door locks, actuators etc. So the BCM can activate the rear door locks even with no rear door switches there.

Now I cannot think WHY the BCM might activate rear door locks/unlocks under your conditions.

 

[ghost_leader07]

Now I cannot think WHY the BCM might activate rear door locks/unlocks under your conditions.

Well i did move the wiring harness beneath the carpet while working on sound deadening the truck I've also took the BCM with fuse box out of the vehicle before doing all of that everything worked fine. I was careful with the wiring harness and BCM.

All of this is a bit too much for me to comprehend especially with my limited electrical experience but i wanna start the process of elimination by checking the wires you mentioned and I'll probably need to remove the BCM again and carpet to check the wiring harness beneath just to be sure nothing in there is damaged.

Removing the carpet will be quite the task since I've upholstered and semi glued a PU leather to the carpet to keep it in place but i believe it's doable with minimal damage i hope.

Thank you and I'll keep you posted.

 

[TJBaker57]

Now I cannot think WHY the BCM might activate rear door locks/unlocks under your conditions.

I do have one speculation/guess.

When some one locks/unlocks the doors the switch they use does not actually do the locking/unlocking. The switch causes the door module to do the one door lock it is connected to and also to send an instruction to the BCM to do the rest of the work. The BCM then does the work of the rear doors lock/unlock and sends a message on the network for the respective modules to do the lock/unlock of the other doors and liftgate.

When these other modules do their task the report back the status of the locks they control.

So here comes the guess..... If there are no DDM and PDM to do those locks then the BCM will not get the answer back that those doors are locked/unlocked. Maybe that causes the BCM to repeat the action/instruction multiple tries??

 

[TJBaker57]

Removing the carpet will be quite the task since I've upholstered and semi glued a PU leather to the carpet to keep it in place but i believe it's doable with minimal damage i hope.

Personally I would hold off on removing the carpeting until other avenues are checked out.

 

[TJBaker57]

tested all of the fuses and all are good

But have you checked for 12 volt power at the specific fuses for the DDM and PDM?? Rear fuse lock fuses 10 and 12 are DDM and PDM.

After those test for 12 volt power at Circuit Breakers 2 for left door and 1 for right side door?

Then test for 12 volt power at the door modules harnesses. The orange wires should have 12 volt power, 2 wires at each switch module.

All of these things I just listed should have 12 volts all the time, even with no key on.

 

[ghost_leader07]

So here comes the guess..... If there are no DDM and PDM to do those locks then the BCM will not get the answer back that those doors are locked/unlocked. Maybe that causes the BCM to repeat the action/instruction multiple tries??

That's a good guess and it would explain the multiple locking sound that occurred before.

I did unplug the battery for a half an hour trying to reset things but that didn't work. I'm thinking should i unplug the battery and BCM in the rear seat for 24 hours and plug everything including the DDM and PDM maybe it reset things? I mean since i ran it without any switches (i mean every switch was unplugged 4wd switch, rear wiper switch, climate control..etc. sorry if this sounds a bit dumb.

 

[ghost_leader07]

But have you checked for 12 volt power at the specific fuses for the DDM and PDM?? Rear fuse lock fuses 10 and 12 are DDM and PDM.

No i haven't yet. About the DDM fuse though the previous owner did something idiotic i found the 10A to be blown but they used a thin cooper strand to jumper the blown fuse. I was shocked to see it and worried that it might damaged something in the process..

After those test for 12 volt power at Circuit Breakers 2 for left door and 1 for right side door?

Then test for 12 volt power at the door modules harnesses. The orange wires should have 12 volt power, 2 wires at each switch module.

All of these things I just listed should have 12 volts all the time, even with no key on.

I'm going to follow the steps you mentioned and let you know.

 

[TJBaker57]

So here comes the guess..... If there are no DDM and PDM to do those locks then the BCM will not get the answer back that those doors are locked/unlocked. Maybe that causes the BCM to repeat the action/instruction multiple tries??

So I just somewhat confirmed my guess.

Those who don't know me will find this odd but here in my kitchen I have a drawer with a PCM, BCM, and TCCM powered up and networked together for test purposes.

I just imitated the door unlock action by sending the correct message addressed from a DDM which is not present but I can spoof the message.

The BCM sent the door lock command 8 times before it gave up. You can see the message repeated 8 times here. There were no modules to answer back to the BCM.




There is another part. Driver personalization settings maybe cause a door unlock instruction to be sent when the key is removed?? Mine unlock when I shift to Park.

 

[TJBaker57]

they used a thin cooper strand to jumper the blown fuse. I was shocked to see it and worried that it might damaged something in the process..

It is unlikely to have caused any damage except if the DDM was already bad and pulled too much current That would have either burnt out that piece of copper or burnt up the wiring to the DDM. Now there was a recall of some DDM that had issues when they got wet from the door being opened in rain.

 

[ghost_leader07]

But have you checked for 12 volt power at the specific fuses for the DDM and PDM?? Rear fuse lock fuses 10 and 12 are DDM and PDM.

No i haven't yet. About the DDM fuse though the previous owner did something idiotic i found the 10A to be blown but they used a thin cooper strand to jumper the blown fuse. I was shocked to see it and worried that it might damaged something in the process..

After those test for 12 volt power at Circuit Breakers 2 for left door and 1 for right side door?

Then test for 12 volt power at the door modules harnesses. The orange wires should have 12 volt power, 2 wires at each switch module.

All of these things I just listed should have 12 volts all the time, even with no key on.

I'm going to follow the steps you mentioned and let you know

So I just somewhat confirmed my guess.

Those who don't know me will find this odd but here in my kitchen I have a drawer with a PCM, BCM, and TCCM powered up and networked together for test purposes.

I just imitated the door unlock action by sending the correct message addressed from a DDM which is not present but I can spoof the message.

View attachment 110164

This is actually incredible that you can do that! and actually i know you're very knowledgeable and thorough when it comes to this platform. 🙌

There is another part. Driver personalization settings maybe cause a door unlock instruction to be sent when the key is removed?? Mine unlock when I shift to Park.

Mine isn't equipped with DIC, i believe it's responsible driver personalization settings?

 

[ghost_leader07]

It is unlikely to have caused any damage except if the DDM was already bad and pulled too much current That would have either burnt out that piece of copper or burnt up the wiring to the DDM. Now there was a recall of some DDM that had issues when they got wet from the door being opened in rain.

Ok that's good news!, my environment is pretty dry and no water got near both modules.

 

[TJBaker57]

No i haven't yet. About the DDM fuse though the previous owner did something idiotic i found the 10A to be blown but they used a thin cooper strand to jumper the blown fuse. I was shocked to see it and worried that it might damaged something in the process..


I'm going to follow the steps you mentioned and let you know

This is actually incredible that you can do that! and actually i know you're very knowledgeable and thorough when it comes to this platform. 🙌


Mine isn't equipped with DIC, i believe it's responsible driver personalization settings?

That may be correct. I do not know.

 

[ghost_leader07]

Hey @TJBaker57 i tested the two orange wires at both DDM and PDM connectors and it shows 12v, I also checked both DDM and PDM fuses and circuit breakers and got 12v at every pin. as for the connector at the rear passenger side i did a quick visual check and it looks solid. what should i go for next?

i have disconnected both terimnals on the battery and i'll let it set for 24 hours, i thought maybe i can get the BCM to reset and do the unlocking command that i heard before but this time with both DDM & PDM connected, do you think it's possible to reset it that way?

 

[TJBaker57]

Hey @TJBaker57 i tested the two orange wires at both DDM and PDM connectors and it shows 12v, I also checked both DDM and PDM fuses and circuit breakers and got 12v at every pin. as for the connector at the rear passenger side i did a quick visual check and it looks solid. what should i go for next?

i have disconnected both terimnals on the battery and i'll let it set for 24 hours, i thought maybe i can get the BCM to reset and do the unlocking command that i heard before but this time with both DDM & PDM connected, do you think it's possible to reset it that way?

When you previously said both driver and passenger switches were "dead" did this mean they just would not do anything at all? That is why I suggested to check for plwer to the switches. When testing the power at the switch harnesses did you ise a frame ground or the ground in the harness wires?

 

[ghost_leader07]

When you previously said both driver and passenger switches were "dead" did this mean they just would not do anything at all? That is why I suggested to check for plwer to the switches. When testing the power at the switch harnesses did you ise a frame ground or the ground in the harness wires?

I used the frame ground.

 

[TJBaker57]

I used the frame ground

So that leaves the possibility that the grounds to the door switch modules are not good. Seems unlikely that two different grounds, for the drivers side and passenger side modules are bad, but you did have all that taken apart no? Those modules ground low on the pillars I think.

I just did another test here using a DDM I had laying around. I wanted to know if the modules would do anything like roll their own window up/down or actuate their own door lock if they do not have the serial data line awake. Nope. Without say-so from the BCM on the serial data bus they sit there like dead ducks. Once I connected the data line from the DDM to the rest of this mess the DDM came alive and I can hear the relays inside clicking even though there are no actuators even present here.

So even if we have power and ground to the door modules, if the data network is not working to these modules they won't do anything.

 

[ghost_leader07]

Those modules ground low on the pillars I think.

I used that ground point to test the DDM and PDM connectors

So even if we have power and ground to the door modules, if the data network is not working to these modules they won't do anything.

Remember the unlocking sound of the BCM trying to communicate with the modules? Does that mean there's data network single? Is it possible that the BCM gave up after many attempts and could need a hard reset?

Even the rear wiper/washer and key fobs stopped working approximately around the same time the DDM and PDM stopped working, again they were disconnected for a long time I even drove without them for a while.

How should I go about testing the data network for these?

 

[TJBaker57]

Does that mean there's data network single? Is it possible that the BCM gave up after many attempts and could need a hard reset?

Doubtful about any BCM "hard reset".

The truck starts and drives right? It cannot do that with a dead network.

Are there any other functions not working beyond what has been mentioned? The DDM and PDM and LGM seem to be the only affected modules/functions that we have spoken of here.

The network operates like this: Every system has a module that controls the functions of that system. They all need to communicate with each other, especially the BCM. The BCM controls the operational status of the vehicle by instructing the modules when to wake up and what to do or not do. All the modules have a single wire that connects them together with all the other modules for communication.

There are two spots where these wires group together. Under the left end of the dashboard is the main junction where the Powertrain Module, HVAC module, Radio, Instrument Panel, Brake module (EBCM), 4WD module (TCCM), Airbag module (SIR), OBD2 port, all tie together. From this point there is a single wire that heads back to the other "splice pack" under the right rear seat where all the cabin modules tie together. The DDM, PDM, LGM, VCIM (vehicle communication interface module), Amplifier and DVD Player (if equipped).


Notice that all the modules that are inoperable here are connected at that rear splice pack. If there was a break in the wire that ties the front splice pack to the back splice pack it would cause the troubles you are seeing.

If you have a meter that reads resistance and/or continuity you could test that wire by locating the front splice pack and the rear splice packs, then remove the "combs" from the packs to isolate that wire, then read the wire between the front to the back splice pack. There should be practically zero resistance in that wire between the two splice packs.

Here is what the front one looks like. You can see the dark blue/white wire there...

 

[ghost_leader07]

The truck starts and drives right? It cannot do that with a dead network.

It does start but i have P0171 code which I'm going to tackle soon other than that it runs ok.

Are there any other functions not working beyond what has been mentioned? The DDM and PDM and LGM seem to be the only affected modules/functions that we have spoken of here

(DDM, PDM, REAR WIPER/WASHER, KEY FOB) thr rest is working well.

If you have a meter that reads resistance and/or continuity you could test that wire by locating the front splice pack and the rear splice packs, then remove the "combs" from the packs to isolate that wire, then read the wire between the front to the back splice pack. There should be practically zero resistance in that wire between the two splice packs.

Here is what the front one looks like. You can see the dark blue/white wire there...

Yeah i have one but the distance between the splice packs you mentioned seems to be a bit long for the multimeter probes, will using a wire to extend the probes affect the reading?

So if i used the continuity option on my multimeter and i got single it means that canbus wire is good? I can rule out a wiring issue correct?

 

[TJBaker57]

DDM, PDM, REAR WIPER/WASHER, KEY FOB) thr rest is working well.

To be clear, the rear wiper/washer and key fobs are all functions of the LGM.

i have one but the distance between the splice packs you mentioned seems to be a bit long for the multimeter probes, will using a wire to extend the probes affect the reading?

As long as the wire is in good shape there should be no appreciable problem using some wire to extend the meter test leads.

So if i used the continuity option on my multimeter and i got single it means that canbus wire is good?

Technically speaking there is no "canbus" involved here. The term 'Canbus' is generally considered to be the standard ISO 15765-4 protocol which uses 2 wires. Your vehicle uses SAE J1850 VPW Class II serial data and has only one wire.

I can rule out a wiring issue correct?

Testing this wire will prove or disprove only that this wire is sound.

That said I cannot right now think of a different wiring trouble that would cause what issues we are seeing here.

If ANY of these communications wires got shorted to ground, the entire network would go out and the truck would not run. So a break in this dark-blue/white wire is the only thing I can guess could be the trouble here.

It seems unlikely that 3 modules, DDM, PDM, LGM, could all go bad at the same time.

 

[ghost_leader07]

Testing this wire will prove or disprove only that this wire is sound.

That said I cannot right now think of a different wiring trouble that would cause what issues we are seeing here.

If ANY of these communications wires got shorted to ground, the entire network would go out and the truck would not run. So a break in this dark-blue/white wire is the only thing I can guess could be the trouble here.

I'll test the wire you mentioned for continuity and let you know.

Does the BCM have a ground wire? I can't find any only the red thick wire for power.