Mechanics

SPEEDOMETER

1994 Saturn SC1

Electrical problem
1994 Saturn SC1 4 cyl Front Wheel Drive Manual

I have a 94 saturn sc1, just recently the speedometer stopped working. So far as I know the wiring in the dash is fine, no fuses are blown, and the speed sensor is ok. I dont know what to look at next.
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Milo15618
September 23, 2010.



How do you know the speed sensor is good how did you test it?Also do you have a any code's?You probably have a bad seat belt module under your center console that control's your power seat belt's. The speed signal has to go threw that module before it get's to your speedometer.

Saturntech9
Sep 23, 2010.
I completely switched out the speed sensor for a new one and it didn't make a difference. The only code that comes up is 26 which the book says is the quad driver module. I've also checked the TPS with a volt meter and that seems to be working fine. However this is the first time anyone has mentioned anything about the seat belt which have occasionally been acting up. The only thing they are doing though is rolling back when the key is in and turned to run. That and the chime for the lap belt starts. This only happens occasionally though.

Tiny
Milo15618
Sep 23, 2010.
The seat belt module is part of that quad circuit and a bad one will set a code 26 and or a code 27 quick quad fault. The reason the speed signal goes threw it is because when the car reaches about 13 mph the power seat belt will close if the drivers door is open if the seat belt doesn't close and the seat belt close's other wise then you have a bad seat belt module.

Saturntech9
Sep 23, 2010.
Makes sense, is that something that can be checked with a meter or anything? And how would I go about repairing it or replacing it

Tiny
Milo15618
Sep 23, 2010.
They way I check them is put the car up on the lift with the front wheel's off the ground with the driver's door open put the car in drive and spin the wheel's to about 20 mph and if the drivers power seat belt doesn't close then you have a bad seat belt module. If you have a jack and jack stand's you could raise the front wheel's off the ground with the ebrake on and the rear wheel's blocked. Why don't you do that to see if the seat belt close's and let me know what you find and we will talk about what to do next.

Saturntech9
Sep 23, 2010.
Ok so I did that and it seems to work how its supposed to. Pretty much as soon as I hit the gas the belt closes. Whats next?

Tiny
Milo15618
Sep 24, 2010.
Alright the speed signal is going into the seat belt module but we don't know if the signal is coming out of it. The problem i'm having is I can't find a wire diagram for the speed signal circuit to tell which wire's go where if memory serve's right I think it goes from the seat belt module to the inside fuse box to the speedometer. The way I always test it is I have a tester seat belt module I swap it with most of the time it work's and tells me that the old one is bad. Let's try this under your ebrake handle pull your ebrake all the way up. You will see a access door pop that off then look into the hole you will see a black box that is your seat belt module see if it's cracked or all sticky and look's like thing's were spilled on it. Let me know what you find.

Saturntech9
Sep 25, 2010.
Ok so I've found a black box with the letters TRW On it. It is cracked and covered in dust and crumbs but not sticky at all.

Tiny
Milo15618
Sep 25, 2010.
I emailed you some wire diagram's let's try this unplug the connector to the seat belt module that has the dark green wire with a white tracer on it the wire will be terminal H labeled on the connector. Then see if your speedometer work's. Let me know what you find.

Saturntech9
Sep 26, 2010.
I have a hard time reading the diagram, it shows up kinda blurry. I could not find anything that was labeled with an H and two of the connectors have a dark green wire with a white tracer on it. I tried disconnecting them one at a time and seeing if the speedometer worked but it still did nothing.

Tiny
Milo15618
Sep 27, 2010.
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