Seat Heaters
From Knowledgebase
Up until the mid 90's, as with many other systems, the Audi seat heating system was basically the same in all models that included it. The system uses a pair of controls mounted in the dashboard for the user to adjust the ammount of desired heat, then via a relay for each seat, heated two elements in each seat. The heating element in the seat bottom contains a small sensor to monitor the heat output so it can be regulated. The element in the backrest is daisy-chained off of the lower element, so a problem in either element will prevent both from working.
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Failure Modes
Obviously there's only 3 basic failure modes - they either don't heat at all, get stuck on, or more rarely will heat as directed but just not at the desired temperature.
No Heat
If you select a heat setting and after 30 seconds or so find your bum to still be cold theres a simple path to follow. As usual, do check the fuse first. Almost all models have a fuse layout chart on or near the lid/cover for the fuse panel that will direct you towards the fuse in suspect.
Check if your other seat heats as desired. If it does the next step is to find the seat heater relays. In most models these relays will be in the auxiliary relay panel above the drivers left knee (you may need to remove a panel or cover). In most cases there will be two tall relays directly next to each other, and on some models (including the type44/5000) there is a nearby labeled diagram. Once you have located them go ahead and switch them with each other. If you are lucky the seats will now have switched which heats. If thats the case pull one out and see which seat it was responsible for (does the working one still work), then you'll know which needs replacement. If the working heater isn't affected by moving the relay try using a pick or small screwdriver to pop the switch out of the dashboard and switch it with the other.
If neither of your front seat heaters work the relay and switch swaping methods won't work for obvious reasons. It's time to break out a DMM (preferably) or a test light.
[To be continued...]
Element Repair/Replacement
If you measure an open connection on your element it's time to replace or repair the grid.
Stuck On
From the Quattro list:
Daughter's '88 90 has a problem that just started today. The heating element for the driver's seat stays on unless the car is shut down. No modulation, and even though the setting is set to 0, it seems to be on full. There are basically three places the problem could occur - in the little controller wheel on the dash, at the thermistor thing in the seat, and at the control relay.
It's unlikely to be the dash thing, since it is just a variable resistor. Though, it could have an internal short.
If the seat thermistor was bad, all it could do is "call" for more heat when the control is set for some, so it's also unlikely.
The control relays are not only most likely, they aren't terribly hard to diagnose.
Undo the cubby panel under the steering wheel (four screws with 8 mm heads, I think), and you find the auxiliary relay panel, which has about three rows of relays.
Look for two identical relays next to each other - they are tall ones, and probably have part number 443 919 533 on them. Pull them out and swap them with each other. If the problem goes to the passenger seat, one was bad. Pull one out and see which seat it ran, discard whichever one wasn't working (or open it up and try to fix it... it may just have stuck contacts). Replace with one from a junkyard.
If the problem stays where it is, the dash controls can be pulled out with a pick type tool, and likewise swapped to see if one of them was the culprit.
-Huw Powell - 21 Jan 2004
Not Heating as Desired
If your seat is heating too much or too little (but IS heating and DOES turn off when the dial os set to "0") the most likely culprit is the switch. Try swapping it with the other switch, a small screwdriver or pick can be used to pop them out of the dash board. If this helps replace the afflicted switch. If swapping doesn't help the problem could also lie in the temperature sensor in the rear of the bottom element, which can only be repaired by replacing the element.
Cody 21:08, 28 December 2007 (PST)
