Thanks for reading. I have a 94 and i have a weird problem with the abs asr system.
At any speed over 30 mph the top 1 inch of brake travel shudders like the abs in on. The abs light does not come on during this. Anything under 30 mph the brakes have no issues, after 10 minutes of driving the service lights come on then the brakes work perfect (except no abs).
I have replaced the battery, cleaned the rear abs sensors, torqued the wheels to 100ft/lbs, replaced the lateral sensor, but the problem still persists.
The codes i get are 1-c12, 9 h75, 9 h76.
Can anybody point me in the right direction?
All this has happened after a stereo install, and did the resistor mod, problem is still there even with stock radio back in.
Thanks
Jeff
They should have a smilie pulling his hair out

 

C=current

12 is the reloop/end of code settings

H=History

75 and 75 have to do with the lateral accelerometer issues, you may need to take a look there, but since they are history codes, they are not active or the problem has corrected itself.

Verify your brake fluid level is topped off, that can sometimes trigger false codes.

 

All the codes are fresh as i reset them when i changed the battery. The h codes are current but as you have to shut the car off to get then they become h codes.
The lateral accelerometer has been replaced as someone else stated that's what 75 and 76 are, from reading codes on line, 75 is low transmission voltage and 76 just gets thrown up.
Brake fluid is in the good zone.
Still trying to find this gremlin.

 

Just because the sensor was replaced, doesn't it mean it is 100% right. Example, my ecm, "refurbished" as new....etc.....2 modules later, finally got one that works.

Not sure how common the lateral sensor is, or if there are core charges when you get a new one, but are you sure it was "factory new" or refurbished new?

 

Some of the initial things I would consider looking at would be as follows and in no particular order:

Condition of brake rotors
Condition of brake pads
Condition of cylinder walls in the caliper and are they leaking any fluid
Do the pads retract correctly and release the rotor
When was the fluid last changed
Fluid level in master
Flex lines


When you say "no ABS", what indication do you have that indicates the ABS (system) is not working. Or are you making an assumption. Or are you talking about the light?


Note:
*** By replacing the battery, it will clear the codes in module 1 and 4 but not module 9 (EBTCM). You have to use the on board diagnostics to clear 9 and use 9.7 and the proper procedure to clear the brake codes.

 

Thank you for the reply.
All the brake parts are good, dont know when the fluid was changes as i just got this one 2 months ago.
I found a post outlining what the car is doing:

Out of the 90 Corvette FSM
Looked in the trouble codes for ABS, I will look further if anyone doesn't like this answer. It's pretty plain what the Lateral Accelerometer is used for.

Code 76
Circuit Description
The lateral accelerometer circuit provides a signal to the EBCM which reflects the severity of a vehicle turn. This information is used by the EBCM to modify the control of the rear wheel brakes to help prevent loss of control in a turn due light brake pedal application at speeds above 50 km/h (30 mph). Code 76 will be set when the accelerometer signal is greater than 0.6g for 120 seconds or more.

My interpretation of this is that if you lightly apply the brakes in a hard turn and the rear tires break loose, the ABS will try to stop this from happening. It will prevent rear brake lockup in a hard turn, trying to control a skid of the back end.

It doesn't appear to prevent control of the normal application of the ABS to the front wheels.

Code 75 5E1-47
Lateral Accelerometer (short to B+ or ground, or open circuit)

Wiring Diagram 5E1-7



General Description 5E1-2 last paragraph
Brake pedal pulsation and occasional tire "chirping" are normal during ABS operation on dry pavement. Also, during light braking in a turn, the rear brake pressure may be modulated to enhance vehicle stability under certain conditions. A slight brake pedal vibration during light brake pedal apply is normal during lateral acceleration levels above 0.6g's and speeds above 50 km/h (30 mph).

with this discovery i am guessing i have a short or ground issue when the radio was changed.

Does anybody have a wiring diagram for this, so i can start to track down where the wiring problem may be?
Thanks
Jeff

 

Before you go off into a tangent, you need to clear module 9 to see if the DTC75 is valid.

If the ABS is activating, you should hear the ABS pump motor running behind you in the compartment where it's mounted.

In reality, the ABS does not activate unless you really crank on the brake pedal and lock a wheel up or slow it down enough to where the speed of it does not match the others and it out of the tolerance window that the brake computer wants to see.

If you pull the fuses for the brake system and ABS, that might eliminate or steer you in the right direction whether you have a true ABS problem or not. If the brakes act the same way with the system temporally shutdown, then you might have a basic brake problem

The wiring diagram for the brake system is very large in the FSM and is integrated into other systems also. It would be impossible to post all this. Specific diagrams and pictures can be posted but not the whole ball of wax.

 

Thanks for the reply
The codes have been cleared and h75 and h76 are current. When the car starts i can hear the abs test happen and no lights on the dic, but when speed of 30 is reached i can hear the abs pumping, when the brake is applies it can be felt in the peddle.
After 10 min of driving the abs/asr lights up and stays on.
I have disconnected the computer for abs and the brakes work fine, so i am leaning towards a wiring problem as this started the day the radio was replaced.
Can you tell me what the wire values and voltages should be on the lateral sensor?
Yhank you for your help
Jeff

 

quick thought. i have troubleshot the ebcm / abs system on the 90+ c4

dying or dead ebcm's can ghost code. i've seen it and it's weird. one car in particular was showing a failed wheel sensor. replaced it, still was showing. traced wires, all tested out.

replaced the ebcm and the car worked fine.

no idea if this is your issue but you absolutely have to keep it in mind with the c4. the abs codes are not always accurate