I have a 1990 740 GL sedan with around 179,000 miles on it, and the heated seats don't work. Does anyone have any ideas on what could be the problem. The car was very very well kept so I can't imagine it being anything too serious. Thanks.

 

I got the same problem with my Volvo. I think this is a great subject, though I did not look at past threads. A great resource, this forum (good people).

 

Do your heated seat lights come on when you flip the switches? Mine come on, but there's simply no heat in the seats. Just out of curiosity. Thanks.

 

In my Saab 9000, the common failure mode for the seat heaters was a broken wire in the seat itself. Usually caused by kneeling in the seat to reach something in the back. The seat heater consists of a wire that snakes back and forth across the seat and lower seat back. There's also a connector between the seat cushion and the back support cushion. It's about an 18 or 20 gauge wire, as I recall. Find the connector (under the seat) and check for continuity with an ohm meter. I don't remember the values but it's close to a short circuit, 8 to 15 ohms maybe? The above assumes normal indication (switch light works and fuses are good). The seat back is probably OK. You can check that one first and get an idea of what the reading should be.

 

Im in the same boat, the lights come on on the switches, but passenger seats has not heat, any info would be great!

 

common sense but did u check the fuse yet?

~jon

 

sometimes fuses is not the anwser mine was a bad element and was in bad need of a rewire
now my seat is hot rockin [sm=icon_rock.gif]

 

The switches have a bad habit of getting dirty inside and losing continuity. The same is true of the power window switches. They are EXPENSIVE from the dealer. Not for the faint of heart, but they can be dis-assembled and cleaned. I've done this on both with success. I did it in a glass cake pan so I wouldn't lose any parts. If one seat is working, try swapping the switches to see if the problem moves to the other seat.

 

It is probably just a wiring issue. Dirty switches or a broken wire/solder somwhere. Should be pretty easy to figure out of you can disassemble the seat (which i don't know if you can ive never tried)

 

you can also find the switches pretty cheap on ebay...

~jon

 

Hi all

Looking for some tips on how to test the seat-heaters in my 1990 740 GL with a multimeter (also looking for insights into the wiring generally)

Cleaned the switches (internally). 12v between power and ground connections on underside of switches (white and black wires respectively, left switch; blue and black wires respectively, right switch) and lights on switches are lit when switches are thrown, but seats still not do heat up.

13.5v across power (red-black) and ground (black) wires at both the floor connections (on the female side) whether the switches are turned on or not.

"OL" (no continuity) on the male side of these same connectors (testing across the pins to which red-black & black wires would connect).

When I first started digging into this problem I discovered fuse #23 was blown. But replacing that fuse made no difference. Fuse #9 is fine (again, switch lights turn on).

I actually don't understand the wiring I'm seeing at the switches (or at the floor for that matter); not seeing much correspondence (perhaps due to my untrained eye) to either the single-output or dual-output seat-heater configs in Fig. 11 here (I've been advised to take online wiring diagrams with a grain or two of salt, however). Not even sure now whether I'm testing the right connectors, though I don't see any other cabling going under the seats...

Thanks for any insight...







UPDATE: Well, nevermind. First of all, was wrong about seats not heating up; passenger’s seat does, just not as quickly/intensely as in my V70. RE: wiring, learned here that there is a relay underneath the seat (in the case of dual-output seat-heater configs, which it turns out my 740 GL has) which either makes use or doesn't make use of that constant 13.5V presented by the red-black & black wires at the female floor connector, depending on whether that under-seat relay is energized to close that "red-black/black circuit" by voltage coming from the white-black wire once the seat-heater switch is thrown (until then that circuit is of course open, hence the "OL" reading at the pins of the male floor connector... though as I am now seeing from my own photo, the "OL" on my driver's side pins is not due to the relay leaving the "red-black/black circuit" open, but rather to the fact that the red-black wire from the connector and the red wire to the heating elements in the seat are clearly detached from the relay!! Might also explain that blown #23 fuse!!).

This under-seat relay (aka "thermostat") is also a thermal cut-off switch, that is, it closes the "red-black/black circuit" when energized by the seat-heater switch but opens it again when a certain temperature is reached.

(Still don't understand the wire colors at the switches but, whatever.)

Leaving all this here in case it might help anyone (I sure have gotten a lot of help on this forum myself)...