All you electrical engineers and microprocessor engineers out there, Any ideas as to root cause for the DDM to involuntary initialize seat heat on some of our H2s? Is there an onboard chip that could be re-initialized or replaced to salvage many of these DDMs that are causing the problem?

 

I have learned that a DDM that randomly invokes seat heat, in fact does not require the seat heat switch to be connected at all. It tells me there is no logic in the seat heat switch itself. Just a box with LEDs and switches. All of the seat heat logic is in the DDM.

 

Give this my best shot, I do know a bit about the PDM (Passenger Door Module) which is likely to be similar to the DDM

So there are 3 possible problem sources, either the PDM, DDM or DMSM (Drivers Memory Seat Module) the latter being located below the left-front seat.

The Door Modules monitor door-switches and control the door lamp-inidicators, they play no actual role in heating the seats, this is handled by the DMSM which directly controls the driver and passenger heater elements (lumbar and seat) and monitors their temperatures.

All the modules are linked via the Serial Data bus, so the PDM and DDM monitor the switch inputs and communicate their settings to the DMSM.

You are correct there is no logic in the switches, the logic is in the Door Modules.

If the door indicators correctly show the heat settings, this suggests something is triggering the module's switches inputs, such as water ingress into the module itself or switch, a short in the wiring or possibly a defective input chip in the module itself.

If the heaters come on without any indicators, this suggests either a faulty DMSM or something is affecting the Serial Data Bus (aftermarket equipment maybe) There is likely to be an on-board chip for the heaters, but if this were defective the heaters would most likely be on all the time.

Also, as you suggest there could be a software upgrade or fix, may be MixManSC could shed so light on this?

Any data/feedback on this would help such as how frequently it happens, the lamp status and weather conditions at the time (raining, hot/cold) intermittent faults are the worse.

 

The lights on the seat heat switch flash like a Christmas tree and you can hear the relays click on and the seats do heat. I went ahead and replaced the DDM which resolved the issue so it's definitely the failure. I don't see any signs of water damage on the DDM; however. All of the other functions within the DDM work fine so it must be an isolated processor somewhere within that module that is corrupted.

 

I'm having this same problem with my drivers side heater coming on and off randomly. It's not the elements becuz it does heat up and I've already replaced them. Can you link the DDM?

 

There are a few different DDM modules and they are expensive. Here is a tip. If you are going to replace it and you have an earlier 03/04 model that does not have the global windows buttons on the heated seats button panel, you may as well get a newer DDM for an 05-07. Then you can pick up a heated seats button panel that has the global windows buttons (or one that has the same buttons for power adjustable pedals which will also work) which are fairly cheap and you will then have global windows.

Also important. If you DO have a newer model that does have the global windows then you will want to be sure you get a later DDM or the global windows will stop working if you replace it with a DDM from an older model.

If you do have an older one without the global windows and are not interested in adding that function I do have a DDM from my 2003 that works perfect I'd be willing to sell. I have once because I wanted to add the global windows feature so I replaced mine with a newer one....

I did a write up on it a couple of years ago and I list all of the newer version part numbers for the DDM's here --- https://www.hummerforums.com/forum/h...-2004-a-38594/

While I paid $50 for the heated seats button panel a couple of years ago I did get the Hummer specific one with the up/down icons instead of the one with the pedals and left right icons but either work to add the global windows. I've seen an H2 with the pedals version before. Here is one with the pedals https://www.ebay.com/itm/184191968925?epid=1711113050 and an H2 specific one https://www.ebay.com/itm/264626007310. The only difference though is the icons on them. The DDM differences are the software. I also found that using a Tech2 it will NOT let you flash the software for a newer DDM onto an older one (which is why I replaced mine).

 

As mentioned I have worked on the similar PD Modue and reversed engineered it's PCB to some degree, but never finished it because I needed it for my truck and simply ran out of time. The PCB uses a 64-pin Motorola MC68HC908AS60AVFU 8-Bit CPU with FLASH memory which seems to directly monitor the switches, if the CPU inputs are defective then it would need replacing and re-flashing. The chip I can change, but re-flashing it is unknown, on the plus side is that it mush have been done originally.

If I could get my hands on a DDM, a defective one would do, then I could reverse engineer it and find out what the root causes are.

Electronics is interesting stuff to me, engines I have no idea about!