Really odd ABS sensor problem: mechanic has no idea, need help
 

I had my right rear ABS sensor replaced today, but my problem is not solved. here is my story/issue:
In July, I got TCS/ABS/SLIP lights on dash. Took to to mechanic, who uses a SNAP-ON MODIS scanner, and he got right rear open ABS code. We turned off the car and cleared the codes and it came right back. I told him I would wait until winter approaches to get it done. I made an appointed last weekend for today, and he replaced the part (he got it from the dealer). The warning lights, however, did not go away after driving and clearing the codes multiple times. He re-scanned the car, got right rear abs sensor. Cleared it, scanned again, and got LEFT rear sensor. The left rear then stayed. He put the car on the lift to test the sensors and got alarming results...
The right rear sensor registers as the right FRONT sensor.
The left rear sensor reads 115 mph, whether the tire is moving or not. The front to sensors read that the engine RPM increases. The tests on the lift were done with the car off.

So I ask you, does anyone have any idea what is happening with my car!

Thank you so much!

maybe the ABS module is bad?

That was the mechanic's best guess, but he was really at a loss for words, and he admitted to really not even close to being sure

have you tried to research the problem ???


if the ABS module was good it should not be registering the left rear going 115 mph...


lok through the FSM see if it has any more information regarding ABS

http://www.nicoclub.com/FSM/maxima/2000/

ABS listed under br.PDF

I've looked through it, and seen nothing really that leads me to an answer

well it gives you an ABS diagnosis trouble tree, it shows you how to test ABS sensors....i mean obviously if the sensors are ok, then check the circuit and then the ABS module itself...

usually when things don't add up it's usually the controller or a poor ground ....just gotta see if the ABS module provides the ground to the sensor signal

Sounds like the mechanic's scan tool doesn't work with the Maxima.

He's never had a problem with it with any other car, at least not that I know of. Is there anywhere I can take my car to get a full scan (free)? I know I can't go to Advanceauto or the like cause they only do SES lights

I don't know of anyone that would do that for free. But what codes did you get when you ran the self diagnostics?

Can't recall. first the right rear (no left rear) then the left rear (no right rear). I think right rear was PO32, not sure what the left is. Also have a knock sensor code, unrelated I think.
And im pretty sure the scanner is fine, due to the odd results of testing the sensors with the car on the lift (see first post)

The odd results should indicate the scanner is not compatible with the Maxima. Did any of the ABS diagnostics (w/the scanner) make sense?

I think you are telling me ecu codes. I am referring to the abs self diagnostic proceedure on starting on page BR49 of the fsm. The abs light blinks long pulses then short pulses to give you a code, for example 32.

2slow, I will bring it up with my mechanic, see what he thinks

Dennismik, I haven't done an ABS self diagnostic - do you think something is being lost in translation from the abs system to the ecu?

I suppose I would have to say yes. When nissan builds in a specific self diagnostic, it gives a lot of information. I counted 28 codes for the abs self test. I love the last one, code 85; paraphrased "the ecu thinks the abs control unit is nuts".

I have a vague feeling that 85 could be my problem, haha. I will have to do a self-test then, thank you.
(Still open to other opinions, though!)

Also, you all may be interested that I installed ambient footwell lighting, tapping into my parking lights. The original right rear abs sensor code showed up before that, however, so I do not think that I screwed anything up

I think the abs thing is just unfortunate timing. But as for the knock sensor code the ecu gives you - ignore it for now. Knock sensor code seems to always accompany other codes like o2 sensors, emission controls and a few others. Take care of the other problems and the knock sensor code goes away.

next step is a abs self diagnostic I suppose. thanks! I will tell you all what the results are

I agree that the knock sensor code will go away, too. I'm getting 19 mpg on 90% city driving, and I think a bad KS would dip that around 15.

How is he scanning anything with the car off? Makes no sense.

If the car is up on a lift the ABS/TCS system will go into default off mode as soon as wheels start spinning as the data it's receiving will make no sense to it.

he did not scan it on the lift, he tested the signals/messages the sensors sent out on it (so he could spin the wheels and see if they work correctly). Maybe the car was on, I'm not sure, I have no experience with ABS stuff and I was not there with him.

The sensor is a hall-effect sensor that detects the tips of the ring gear. It sends impulses to the ABS Module for speed and decelleration calculations.

"A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications."

It doesn't read speed, so how is your mechanic coming up with 115MPH looking at the sensor?

Find another mechanic, what he's telling you makes no sense.

after a clutch change done by myself ... my abs light came on and my speedo is no longer working dont have a clue why

maybe you left the vehicle speed sensor disconnected? the one that comes out of the transmission..


either that or the sensor itself is damaged or the wiring harness from the sensor is damaged

The only thing you'd get by manually testing the sensor yourself (as in NOT going through the scan tool or computer) would be voltage. And quite honestly, there's no way to spin a tire by hand that fast.

On another note, if the car is off, a scan tool will NOT work. They car must be KOEO or KOER (key on engine off, / key on engine running) for a scan tool to communicate. I've used a snap on solus pro on my car before, so I don't see why the other snap on scanner would be "incompatible". Check wiring for the sensors and the ABS module, and check fuses as well. See if wiggling wire harnesses or connectors changes any codes that come from the computer. If there's an intermittent short in the harnesses it could change during driving (such as hitting bumps, turning forces, etc). You could also try removing the fuse for the ABS and see if that fully resets itself. Also, if the code kept coming back for the R/R abs sensor, and now the left is coming on, why not try putting the old sensor back in on the R/R? If the old sensor proves to be working then it's pretty much a sure shot that the ABS module and or wiring is causing the issue.

bump
i have the SAME exact issue. Basically my mechanic did all the ohms test and was coming up with the same 115 mph reading....and thats before and after changing the abs wheel sensor. Long story short, before he could have the abs module swapped out, he closed shop and went his merry way. So the big qs is...should i go ahead and change the abs module myself? If so where should i buy one from (ebay?) and how do i swap it...
:cool:

for me the solution was to replace both sensors. they both went bad within a few weeks ago -- but timed perfectly that only one came up, fixed, the other was there (no scan in the middle). So I'd go with the scanner's reading

my mech said that he saw the code and replaced the sensor. The code went away but the lights still stayed lit. I drove the car around for a couple of weeks (1000+ miles) but the three lights stayed lit.
He troubleshooted the damn thing inside and out and was pretty confident that it was the abs module and not the sensor cuz he wasn't pulling any other codes. As a matter of fact, he even replaced the newly installed sensor with another piece just to make sure the sensor wasn't faulty. I'm leaning towards replacing the module out myself. Worse comes to worse i'll be $100 something dollar poorer but at least i'll be one step closer in fixing this damn issue! :mad: