ABS Wheel Speed Sensor Circuit? Issue - Any ideas???

[ccoyle71]

New to joining / posting on the forum - but I've read alot of threads.....and owned my 2004 SR5 since it was new. Great car. I love it - and it's been mostly minor maintenance for 250K miles. Tires, brakes, oil changes.....I did have a brake issue - but all in all - very minor. Here's what I have going on now......

I'm driving earlier this week in the snow (mine is a 2WD) - and my check engine light comes on along with ABS light, traction assist. I quickly noticed that my speedo also wasn't working. The tach and other gauges seemed to function, so I finished my drive to work and checked the codes. My scanner only does engine codes - and I got a P0500 - Speed reference sensor or something like that. Made sense to me....given the speedo wasn't working.

So - I drove by my friends house on the way home to use his really professional scanner that does all the chasis codes and real time monitoring.....

He got the same P0500, but also a C0200 - right front abs wheel speed sensor. This made sense - so I felt good about picking up the wheel speed sensor (even though it was $100 - geez!

Put it on - and no dice. I'm like what?? So i start checking connectors.....then try it again.....and viola! It works......for about a mile, then drops back to zero. At this point, I'm guessing it's not the sensor - so I take it out, test it (which I should have done before) and the old one measures about the same resistance. I put the old one back in.....and nothing, until I wiggle wires, disconnect the battery, and then it works again. For a bit.....then quits.

So - I'm thinking it's in the circuit - but can't find a diagram, and I'm starting to worry I'm over my head. I'll stop here for now - but happy to provide more detail. Has anyone run into this and found a solution??? Thanks in advance!

 

[AuSeeker]

I suspect that as many who has had similar issues and the sensor tested fine, that they had a damaged speed sensor wiring harness, which was replaced and it solved the issue for most of them.

So my suggestion would be replace the harness to the affected sensor.

You might want to try doing a continuity test on the harness first to help confirm even though it maybe just a bad connector it's sometime not easily fixed permanently and needs the new harness in the end.

 

[ccoyle71]

Ok, thanks. Am I correct that the harness runs from the sensor and plugs into the bottom of the fuse box under the hood?? Mine is passenger side (not sure if I mentioned that) and it appears to run across the grill in front of the radiator, and into the fuse box. Is that box also called the ECU? I'm guessing i need to remove that whole box to get at the wires, correct??

 

[ccoyle71]

I should mention.....I did check continuity between the sensor / connector by the tire.....and the next "connector".....that's located on the passenger wheel well under the hood.....and that section tested fine. But from there - I haven't really gotten to the other end of the wires - which I assume involves removing the ECU??

 

[AuSeeker]

I can't offer any other advice since I haven't had to deal with that issue, I was just saying what I have read on here from others who have had this or a similar issue, hopefully some of those members will respond.

 

[ccoyle71]

Thanks. It's so bizarre......after fiddling yesterday, then letting it sit for a while.....I get in last night, and everything worked. Still had an abs / trac / vsc light on.....but speedo worked the entire time to pick up one of my kids from a friend. 30 min drive, no issues.

It also warmed up alot yesterday in TN - it's been in the teens.....and yesterday was 50 degrees. I've read some posts about the weather affecting issues around abs on these 4th gens......so weird.

I'm the type that doesn't like a single idiot light on my dash....and really want to "solve" the issue.....but who knows, maybe this one I'll just chalk up to I'll never know for sure. I'm hoping after some drive cycles, the other lights will go off....and a zero pt calibration will have me a ok and past this issue.

Thanks again - Chris

 

[ccoyle71]

To close out this thread.....

So after a few drive cycles, my ABS, TRAC, VSC lights went off. No idea. I ultimately didn't replace anything. I did wiggle some wires, and re-seat connections, but honestly don't think that was it, since it didn't solve it the first time I tried that.

It sounds crazy, but the only thing that perfectly coincided with it improving was the weather. I know I've read in some other threads about cold temps, so I guess it's possible?? Could there really be something in the ABS module that just doesn't cooperate with temps below 30 degrees?? Seems like a major achilles heel to me, but I don't know what else it could be. Thanks again, hopefully it's resolved (at least until another week of freezing temps):cheers:

 

[earthrealm]

To close out this thread.....

So after a few drive cycles, my ABS, TRAC, VSC lights went off. No idea. I ultimately didn't replace anything. I did wiggle some wires, and re-seat connections, but honestly don't think that was it, since it didn't solve it the first time I tried that.

It sounds crazy, but the only thing that perfectly coincided with it improving was the weather. I know I've read in some other threads about cold temps, so I guess it's possible?? Could there really be something in the ABS module that just doesn't cooperate with temps below 30 degrees?? Seems like a major achilles heel to me, but I don't know what else it could be. Thanks again, hopefully it's resolved (at least until another week of freezing temps):cheers:

yeah, am a bit late to the parade, its either the sensor or harness, perhaps moisture got into it....it also needs to be driven about 1km, before the idiot lights go off, ie after repairing the cause