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What's Up With My Speed Sensor(s)?


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Ok, so on monday, I took my car up to Watertown to get my speed sensor replaced. Before I go on with this, I'm going to describe my symptoms. I first noticed somethnig was wrong when my speedo started to climb REALLY slowly. A cruise in a 30 MPH zone confirmed something was wrong, as the speedo read around 15 MPH. The highway yielded 30 MPH on the speedo. But then, that night, the speedo was working fine again! The following morning, it was messed up again. It seems engine temp, time of day, nothing seemed contributed to this odd behavior. A rather expensive OBD-II scanner pointed out that there was nothing wrong with the dash cluster, as the speed being registered on the scanner (while driving) was the same as the speedometer.

So on monday, they replaced the main speed sensor (the one right on top of the transmission when you remove the airbox. I thought that fixed my problem, but tonight a trip to the local 24 hour convenience store revealed that i was still having issues with the speed sensor(s). My question is: What is going on??? Sorry for the long post, but I needed to get a few things across. ANY help would be appreciated. Thank you for reading.

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Well for starters most generic scan tools only read the ECM, so you aren't going to find any codes anyways. People only rush to answer questions that they know the answer to. You ever thought the problem might be in your gauge cluster?

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There are sensors at the wheels. 4 I think, one at each, I can only confirm the fronts. I recently had a prob with my speedo not working. It turned out the NH winters cause salt to eat away at the wiring, I replaced a total of 4 feet of wire between the 2 sensors. Everything is OK now.

Does your ABS/Tracks light flast during the POST test? Or what ever car guys call it when you fist turn the car to the "ON" position?

If not, I would suspect the ABS unit is bad. Use a heat gun to loosten the seal on the unit, you'll see the broken solder joint, just remove the old stuff and re-solder. Use a silicone sealant on the ABS unit afterwards to close it back up.

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Well for starters most generic scan tools only read the ECM, so you aren't going to find any codes anyways. People only rush to answer questions that they know the answer to. You ever thought the problem might be in your gauge cluster?

but its not the cluster. we hooked up an obd II to the car and checked to see if the speed registering to the obd II was different from what the dash said. if it was different, then we would know that the cluster was to blame. however, the odb II read the same exact thing as the cluster, pointing out that one of the speed sensors was to blame, as the dash merely relays what the sensor tells it too.

It's not an ABS problem. the whole ABS system seems fine.

PS: yeah, i guess your right. i was just getting irritated about the problem and over reacted. sorry.

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The speed sensor still passes signal through the ABS/TRACS module so if there is an issue in there than it will throw off the speedo.

I would check out the ABS/TRACS system.

wouldnt that throw on an ABS/TRACS light? how trhe hell do i check it? i looked in the haynes for the car, but the haynes is really quite vague and useless.

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ever consider buying the Volvo service manual? might be worth the $50 or-so bucks to be able to actually test the components. then again, swapping parts is fun! :monkey:

i have it. it's useless. the model car they use is a base v70. i cant locate a goddamned thing in that book because all they show is that blasted 2.4 liter. they're really not that similar.

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