90 LS400 has traction system. The trac OFF abs OFF lights are on. Checked the codes and it gives 35. pointing to rear right or front left speed sensors. I've changed both sensors one by one but the error code is still there. Any ideas what else to trouble shoot after this ?
I went to the dealer and they didnt have an answer either. They simply said i should try to change the sensors again...

 

I haven't looked on a 1st gen LS, but on many other cars, a loose wheel bearing will cause a speed sensor issue due to a high variance in the signal quality... being that it is the pair of them, there might also be another failure... I'll look it up in Identifix and see if I can find anything for ya in a bit..

 

thanks very much ! i appreciate the help. actually I had some rear suspension work done by a local body shop. it was after i picked up the car that the trac/abs light was on. the shop refused to admit they did anything wrong. upon inspection it turned out that the rear right sensor was broken and someone had tried to solder the connections back on the sensor itself. so obviously they tampered with the rear right sensor. Since then I've changed the rear right sensor twice. without any luck of getting rid of the code 35. I then also changed the front left sensor as those two sensor generate a code 35. code still there....

 

Question, did you actually reset the system???? Looks like there is a specific procedure for that on those guys...

To clear ABS codes, jump the TC terminal to the E1 terminal in the diagnoses box in the engine compartment. With the terminals jumped, turn the key on and pump the brake pedal 8 or more times in 3 seconds. When cleared, the ABS light should continue to flash rapidly . If the code didn’t clear, the ABS light will flash a code after the brake pedal has been pressed 8 or more times.

 

yup did that. and just to double check i'm going through the right procedure, i unhooked the other side's speed sensor and that gave a code 36. then i cleared the code after hooking the sensor back as well and code 36 went away. code 35 persists...

 

man, I've been looking at the wiring diagrams, but those sensors go directly into the traction control module... the only other thing I can think of would be the control module itself being bad...

edit: one more thing - does the light turn on as soon as the car is started, or do you have to drive for a certain amount of time?

 

here's the doc i'm going by. if the module were bad according to this it would give a different code... i'm baffled myself...

another question i have is, can i simply plug a new sensor at the connectors and check for bad sensor or would i have to install the magnetic part in the rotor as well? cause the electronic module is apparently only checking for "open or closed circuit" which i'm guessing should not be dependent whether we plug the sensor in it's place next to the brakes or not... any ideas ? thanks again for all your help. much appreciated !

 

Yah, looking at the trouble code, it thinks there is an open in the circuit...

There are two scenarios I would test here - I would test continuity between each of the wires going to both of those sensors and the ABS/TRAC control module... if the wires show good continuity, I would try swapping sensors side to side and see if the code follows the sensors... if the code follows the sensors, then you have a bad sensor, but if the code persists and you know the wiring is good, then the ABS/TRAC control module is bad. It may have a short inside - not necessarily a control module fault that it could sense, so it wouldn't throw a code for itself, but just an open in that circuit inside...

 

i have 04 GX470 with similar problem which dealer is trying to fix, it's been 2weeks and still don't have straight answer. I had 3lights ABS, TRACOFF, TRAC(forgot what this one was) and took it in and they found a code that led to abs ecu($1800 on part) which was replaced. they test drove it after the repair and same light came on but with different code which led them to front speed sensor, they have checked the actual sensor which seemed okay but still can't get it to fix. like i said it's been 2weeks and no definite answer....

 

Well I tried swapping sensors today. No luck. Now I have to find out if there's good continuity in the wires. Can someone tell me where the wire from the rear sensors go to the front of the car. More over, how would I check the circuit given the wire is way too long for a multimeter to be hooked up to it...
thanks.

 

just get longer leads for your multimeter... at the shop, we have a (quite pricey) fluke multimeter that has extensions for it's leads... they are just normal wires...

 

almost a year of testing and going to dealers yet no solution. I'm surprised none of the dealers know what is wrong with it...

 

Might be a stupid question, but did you erase the code after replacing the sensors? And then you got it again?

 

yes it doesnt clear up.

 

question:
given the abs/trac off light comes on after the car starts even without driving, that leads me to believe that the abs ecu is checking simply for continuity and closed circuit at that time.
therefore, if i were to swap the abs sensor at the connections and not install the sensor in the wheel well, will that test still work to see if the sensors are faulty or not ?