nyteacher08

Greetings fellow F body owners, My name is Peter and I am restoring a 1993 Z-28. This is my first chevy. I love this car !!! However I am having an issue. I have an ABS INOP and BRAKE light on. I replaced all three sensors and replaced the front rotors and pads. All my lights are working, and I cleaned the e-brake switch all good. Fluid level is full. I noticed the lights come on only when the car starts to move, forward or reverse but right before they come on there is a click sound coming from abs unit under hood and then the lights come on. they only go off when I shut the car off, but come back on when I move it. abs was scanned but no codes?? I cleaned the two grounds on each side of the radiator. No luck. I am going to change the rear pads and rotors because they are low. pleeeeeeeeeease HELP!!!

pgerst

Scanned with no codes? I am unaware of a dash failure that would cause both lights to fail "on." Was the abs scanned with a GM "tech" scanner as the ABS is proprietary and none of the budget scanners will read the ABS codes. Based on your symptoms, my guess is ABS motor pack; but replacing ABS components on these cars on a guess is a good way to burn money. I would get access to a GM tech1 or 1A and see what the codes are.

Injuneer

Interesting thing.... here's a guy on another site (he is also a member here) who has written software to scan the OBD-I PCM, EBCM and SIR modules (he's using a 94/95 PCM, so remains to be seen if it is 93 ECM compatible):

Gonna try my hand at writing an OBD1 scanner app - Firebird Nation

nyteacher08

For pgerst , thanks for the advice, I am taking the car to Chevy tomorrow and letting them scan it. I think It may be the Abs module. For Injuneer thanks man, Let me know if the software is for 93. Ill update you guys on what Chevy says if you want.

nyteacher08

O.K. got the car back from Chevrolet...... One code DTC 24. VSS sensor . My right rear wheel is registering then dropping off then registering. Dealer said its either the reluctor ring....... which I can no longer buy from anywhere because I have 3:23 gears or its the wires for the rear sensor. need to check wires first. Then .... I don't know.

Injuneer

A bit confusing. DTC 24 is for the "vehicle speed sensor" mounted on the output shaft housing of the transmission. Is your speedometer working? That code is read from the ECM, not the EBCM. Looking at my 94 manual (which may or may not match the 93 ABS system), the EBCM DTC 24 is for the "rear wheel speed = 0". That's the sensor on top of the differential housing, reading the reluctor gear on the carrier.

You indicate "My right rear wheel is registering then dropping off then registering." There is no right rear wheel sensor on a 93. The right and left wheel speed sensors are only used with traction control, and traction control was not available until 1995 model year.

Then you mention a reluctor gear, and relate it to the 3.23 gears, which would be the single rear wheel speed sensor that is mounted on top of the differential housing. Which brings us full circle.

nyteacher08

Not sure what to say, I had the rear sensor changed 3 times. But Chevy says the problem is the right rear wheel not registering consistently. Even though there is only one rear sensor, the right rear wheel is giving it problems. Must be wiring is faulty. They suggested its either the reluctor ring missing a few teeth or have the wiring checked from the sensor to abs module. They said get it ohm tested to see if there is resistance? if there is resistance its the wiring that's bad. I don't know. We will find out eventually.

Injuneer

I don't know what to say either. There is a reluctor, a sensor, and two wires from the sensor to the EBCM - one black, one white. There are two additional connectors in the path from the sensor to the EBCM - called the ABS jumper harness. When you replaced the rear sensor, did you inspect the harness terminals for corrosion?

There is no possible way for the EBCM to determine ONLY the right rear wheel speed. I downloaded the 93 shop manual and reviewed it, but the ABS section is not included, with the indication that a supplement would be issued later. The only reference I have is the 94 ABS manual. In the 94 manual, there is a code "35" the is labeled "RR Wheel Speed Sensor Open or Short to Ground/Batt". The "RR" means "rear", but is it possible your dealer is interpreting that as "right rear"?

Given the large number of teeth on the reluctor, I doubt a few missing teeth will produce a "0" speed reading. Might produce a slightly erratic reading, but never a "0".

nyteacher08

I hear what you are saying, it really makes sense. I will have the abs jumper wiring checked out soon. thanks for taking the time to help me, means a lot to us. I will keep you up to date as an answer develops.


Thanks,

Pete

bwellard

Hi There, did you figure the problem out??? I have the same indicator lights on and the dealer was less than helpful.

Thanks Barry