[turbojimmy]

Hi all,

This is a loooooooong shot but here goes.....

I'm trying to figure out why my heated seats in my DTS don't work. First it's a flood car. The front seats are original (and thus have the flooded heat elements in them) as is the rear seat bottom. The rear seat back is out of a collision total. The only heat that works is in the rear seat back. Since the rear seat back is the only part that was not under water I assumed that the problem must be with the elements.

I ordered up complete sets of elements for the front seats. I installed the LH cushion elements yesterday. They don't work.

I've run through the diagnostics and I'm pretty perplexed at this point. The resistance of the new elements is obviously good - under 6 ohms. The rest are bad - 30+ ohms. I figured at least the new seat cushion elements would work, but no.

So I got looking at how it works. The module senses resistance to know how hot to make the seat. High resistance = hot. Thus, if the module senses high resistance it will shut off the power to the heat. It appears as if the seat back and seat cushion elements are sensed and controlled separately. Even so, I thought maybe the baked seat back element could affect the seat cushion, so I unplugged it (unplugged = no resistance). Still doesn't work.

I'm getting juice at the module. When I put a voltmeter on the heat element supply I can see a blip of 12+ volts from the switch and then it goes away. From what I understand, the module counts the 12V pulses to know how much heat you want (low, medium or high). Once you get that initial 12V, the module will apply enough voltage to heat up the element based on the resistance (i.e., how hot it is already). When I test the seat back circuit on a working rear module, I can see the module ratchet down the voltage on the high-med-lo settings.

So, I moved a working rear module up to the front and it didn't work. Now, in the rear I only have the seat BACK working. When I moved that module up front, I got nothing out of it but I know the front seat BACK is toast. What's weird is that when I put the rear module back where it belonged, it didn't work at first. I hooked up a voltmeter to the input on the known working rear heat element and I was getting nothing from the module (except for that split-second of 12+ voltage). After a few minutes, however, it began working again.

So now I'm not sure where to go. Since the backs and cushions are monitored and regulated separately, I'm wondering if the flooded elements have baked their respective parts of the modules: cushion/back in the front, and cushion in the rear. Thus, when I move a rear module up front to try to get the cushion to work it won't.

I'm baffled at this point. It can't be a short to ground in all 4 seating positions, which is the only option the diagnostic procedure gives me.

Should I invest in a new module to test with?

TIA,
Jim

 

[turbojimmy]

As usual, I'm going to reply to my own post.

I goofed around with it some more and both back modules are putting .25 volts to the cushion, and 14.xx volts (engine running) to the seatback. That explains why the seatback is warm and the cushion is not. I checked both cushion elements and they both have 12+ ohms of resistance - enough to make the module think they're warmed up.

Now here's the thing. When I unhook the heating elements, the module still puts out .25 volts like they're still hooked up. So do the modules have some kind of memory? When I put the same module up front, with the new cushion heaters, it didn't put out anything to the cushion.

I might spring for a new module to goof around with.

Jim

Jim

 

[ccclarke]

Jim,

This sounds like a good problem, and you're doing the right steps to isolate it. I don't have the schematic, (so there's some guesswork on my part involved here) but I have to wonder about the way the circuit is operating as far as the 12vdc pulses to set the output levels from the modules. Your post indicates the resistance of the heaters is subject to change while loaded for different temps (low/med/high). This seems odd, (like I said, I don't have the prints in front of me) but generally with heaters, the resistance is going to be the same no matter how much or how long voltage is applied. What does change is the current output of the controller (3 outputs for three temp levels). My vehicle has a Low/High setting without a thermistor to send feedback to the controller. You select a temp, and the heating element receives the proper current and in turn produces a set wattage. The seat heaters stay at the same temp until I turn them down or off. Maybe the DTS incorporates a thermistor to monitor temp; if so, it will be on the dwg.
On to the troubleshooting part: Rather than buy a (expensive?) module, it might be a little cheaper to pick up a couple of high wattage 6 ohm resistors to simulate a load and monitor the current with your multimeter first. Place the loads in the connector for the output circuit/seat position to be tested. The module should vary it's current output depending on temp. If you can't get any output from the module, it is highly suspect as long as the controller is sending the proper command pulse or whatever it uses for temp. control. Any car with flood damage is likely to develop connector-related problems over time, so a close visual/electrical inspection of all connectors in the affected circuits is a good idea. It sounds like you've had this problem since you acquired the vehicle (right?) so its unknown how long after the flood damage the car's electrical system was energized. Moisture on the circuitboards may or may have not had enough time to evaporate, which may have contributed to the problem. If the seat cushions held moisture (as they're prone to do) like sponges and the heater circuits were energized, they could have fried part of the controller/heater module circuits. (Low resistance would have tricked the controller to a max output condition). Keep us posted on this problem. I wish I could offer some concrete steps, but without the schematic to understand how your particular circuit is supposed to work, I can offer only general tips. Good luck!

CC

 

[turbojimmy]

CC,

Thanks for the reply. Your suggestion about using the resistors is a good one - I'll try it.

I wasn't totally clear on the operation. The system is supposed to work as you've described. The current is regulated by the module depending on the resistance through the thermistor. Each set of elements (cushion or back) has a 4-wire connection: 12V+ supply from the module, a regulated ground from the module, and 2 for the path through the thermistor. The thermistor should read between 280 and 300 K ohms. The resistance through a cold element should be less than 6 ohms (for the cushion, the back is higher I guess because it's bigger).

According to the FSM, the pulses of 12V are so the module (I forget whether it's the door module or the heated seat module, but both are involved) can count the number of times the button was pushed. Once is high, twice is medium, three times is low and a fourth time is off. Using the thermistor, the module keeps a steady temp at each setting (107.6 degrees on high, 103.something at medium, and 98.6 at low).

With the module that is working, I can see these blips at the heating element before it begins to regulate the current.

Anyway, the car was completely disassembled and allowed to dry out about 2 months after the flood. I had the foam seat cushions in the furnace room of my basement drying for a few months. There wasn't much corrosion at any of the electrical connectors either, but I did take every one apart and clean them and reassemble them. When working on it yesterday, all of the connections look fine. All of the electronics in the car are either new or out of a collision-total. The heated seat modules are out of the collision-totaled car, however it did in the salvage yard for about 6 months with no windows. Most of the pertinent electronics are buried up under the dash, behind the rear seat or inside the door panels. The front seat modules, however, are under the front seats. They may have gotten pretty wet - not sure. They are 'clicking' like they're supposed to, but I'm not getting any voltage out of them other than the 'blips' I described above.

Thanks for your help!

Jim

 

[turbojimmy]

So I rolled the dice on a $85 heated seat module. It will be in later this week. If that's the problem, I'm only going to fix the 2 front seats. If the modules are indeed bad, the back seat is going to cost about $400 to fix in parts alone. The backseat passengers will have to live with cold butts. I've already invested the $100 per front seat in elements, so I may as well spring for the $85 modules (assuming that they are the problem).

Going through all of the diagnostics and studying the wiring diagrams I can't really come to any conclusion other than that the modules are bad. There are only 4 parts to the system: the switch, the door module, the heated seat module and the elements. All are testing and behaving as they should except the heated seat modules. The heated seat module alone senses the resistance and regulates the current. All I can figure is that operating the heated seats with the water-damaged elements must have baked the modules.

We'll see when the new module arrives......

Jim

 

[ccclarke]

From your detailed symptom elaboration of the fault, the modules definately sound suspect. Let us know how it works out. Good luck!
CC

 

[turbojimmy]

Well the module didn't do it. But I'm wondering if I have the wrong module or something because this new module isn't doing anything at all. No clicking, no heat. The P/N is the same for all years 2000-2005, but my manual didn't have a P/N for the front so I ordered up a rear module. The existing ones all have the same P/N on them.

When I'm done working I'm going to go out and test it with a voltmeter.

Jim

 

[turbojimmy]

Okay here's the deal.

In order for the module to work, BOTH the seat cushion and seat back elements need to be operational. As I mention above, I had just replaced the cushion and unplugged the seat back (because I knew it was bad). Even though the schematics show that the heat regulation circuits are separate, they both have to be functional in order for the module to send juice to either one.

I plugged in the new seat back cushion (didn't install it yet) and VOILA! seat heat. This is NOT the way the back seat is behaving, but that's what I needed to do in order to get the front to work.

So, I bit the bullet and replaced the seat back element this afternoon so now I have one completely functional seat (my seat, which is important). The old module works fine, too. So I sprung for a new module uneccessarily. An expensive lesson. I should've tried the new elements first.

Oh well....I'm going to tackle the passenger seat before the weekend is out so I have both front seats functional.

The heat is pretty sweet. I'm glad I took the time to do it.

Jim

 

[ccclarke]

Jim,

Glad to hear the heat is on! Were you able to use load resistors prior to ordering the module? It sounds like the module was expecting a complete circuit through both (seat cushion/seat back) loads; correct?

CC

 

[turbojimmy]

Jim,
Glad to hear the heat is on! Were you able to use load resistors prior to ordering the module? It sounds like the module was expecting a complete circuit through both (seat cushion/seat back) loads; correct?
CC

I did not use load resistors to check the module. If I had, I'd have saved $80-something bucks. But yes, you are right - the module was looking for a complete circuit through both sets of elements (cushion and seat back). The thermistor circuits are completely separate, but the current circuit is shared. The 12V+ to the elements is the same supply inside the module and the current is regulated for each element by a separate ground feed off the module.

The troubleshooting procedure has you check each element to troubleshoot a 'heated seat inoperative' condition but it wasn't really very explicit in that one element could cause the other not to work. I guess that comes with experience (and reading the wiring diagram properly).

I'm going to do the passenger seat today since I have the parts and I know the investment in time will pay off.

Thanks!

Jim