During the monsoons we have been having here on the left coast, I had to hit the binders hard enought to kick in the ABS. A weird thing happened. There was no pulsing and the brakes would not stop the car. I had pedal, just no brakes. Fortunately, I had slowed enough to let the problem pass. I have not noticed this when AX'ing, but I'm on and off the brakes and not trying to come to a complete stop.
I have searched the archives for similar challenges but have found nothing.
The ABS growls every morning as I back out of the garage, no lights, no codes. When braking normally, I have good pedal and stopping power.
Pads are PFC, have S/S lines, using Valvoline Synpower fluid, all fluid is fresh, MC and booster are less than a year old.
I did notice that when bleeding the brakes with a MityVac, the rears did not want to bleed, but using the buddy method, they bled fine, no air.
I have looked for a bleed valve on the ABS module to no avail.
Now the questions -
1 - Could there still be air in the ABS unit?
2 - Could there be a "fault" in the controler that the computer isn't reading?
3 - Could the whole thing be FUBAR?
4 - Can I swap out the entire unit without a bunch of challenges?
I did find a ABS unit from a 87 that looks like mine (attach photos) on ebay but all the books say to "take it to a dealer for service."


91 ABS


87 ABS
I really could use some info here.
TIA
Subman

 

If your back brakes won't bleed by just pressing the peddle with the rear bleed screw open, then i think your bias has gone in the mc. Thats what had happend with mine. About the ABS, i'm sure i read with the synthetic fluid that you must not use it on vechicles with ABS systems? maybe it was just that brand i had.

 

Retrieving ABS codes using ABS light:

Flash Code Method:
1) With ignition off, install jumper wire between pin "H" (White/Tan wire) and pin "A" (Black/White wire) of ALDL connector.

2) Turn ignition on. Diagnostic display mode will remain active as long as pin "H" is grounded, serial data link connection has not been initiated, and vehicle speed is less than 4mph.

3) Approximately 3 seconds after ALDL pin "H" is grounded, EBCM will begin flashing SERIVCE ABS light to indicate trouble codes in sequence. Sequence will start with Code 12to signal the beginning of trouble code display.

4) Each stored trouble code will be displayed 3 times. After all trouble codes are displayed, sequence will be repeated.

Note: Trouble codes 41, 45, 55, 61 and 63 can ONLY be read through ALDL using Tech 1 if trouble code is currently present (current code). The EBCM will not allow any trouble codes to be flashed if any of these codes is current. If trouble codes existed previously (history code), but not currently present, trouble codes can be read using SERVICE ABS light.

Code:
41 - Right Front Solenoid Valve Fault
45 - Left Front Solenoid Valve Fault
55 - Rear Wheel Solenoid Valve Falut
61 - Pump Motor or Motor Relay Fault
63 - Solenoid Valve Relay Fault

Let me know what codes you get (if any) and I can look up the codes for you. Too much to type out.

 

The day my ABS gives me a problem is the day it gets eliminated

 

VetteNoob - Thanks! - will try ASAP and let you know
Subman

 

To bleed the ABS pump, you need an ABS Tester that will allow the pump to run to pass fluid thru it. When you bleed the brakes through the calipers, there is no fluid passing thru the ABS.

It's hard to say what differences there are in ABS pumps between the earlier C4 years but a GM parts list should show any differences or a good brake shop can tell you.

If the pump is bad, you could replace it yourself, but you do need to have a tester that will run the pump to get brake fluid into it. My 92 uses the GM Tech-1 and the brake module to operate the ABS for diagnostics or bleeding.

As far as brake fluids go, do not use DOT5 silicone fluid in ABS cars. The silicone fluid will cause cavitation in the pump and create air pockets. DOT5.1 is apparently OK to use but if you stick with a good quality DOT3 or DOT4, that will be fine.

 

Went through the ALDL to test and got 12 - 12 - 12, nothing else. Google search lead me to CorvetteFever trouble shooting ABS 86-91.
The article said to test the relay(s). Relay (p/n 1636973) checked out ok. Relay 2 & 3 (attached to the pump) it said to check the #9 pin on the connector after the relays. I have 2 banks of connectors - 1 with 8 wires & 1 with 4. I used a 12v test lite and a digital volt meter. Here's a chart of my findings.



I don't know what all this means, what's supposed to be hot and what's not. I do find #11 & 12 weird. Both have 11+ volts but 12v testlite show no or little power.
If any of this makes sense, let me know.
There is also a fourth relay. ID's are 14100455 or D117 or VF4 15F11 Z01. There seems to be no power to any of the wires.
I'm thinking these are pretty inexpensive relays to replace. Can't hurt.
If you've got any ideas, I'm ready to hear 'em.
Subman

 

Emailed you. Not sure what to make of the voltage readings tho. Looks like your relays are close to $20 each from GMPartsDirect.

 

Well I can tell you this if you want to replace the abs unit I have a complete one from a 91 ill sell you for $200 the 87 you posted is similar but they are different!


johnny

 

johnny - hang on to it - will post this weekend if needed. THANX
Subman

 

Ok sounds good!

Ive got it right here!

johnny

 

As stated above, the 89 ABS controller is diferrent from the 91.

I have a 90 and was sent the wrong controller. It was for the earlier version and did not work. Different part numbers. The early versions did not store or report codes.

If you can get the pump and controller for $200, a fair price.

You have interesting problem. When this event occured, were you braking over a large pool of water. Is it possible you were hydroplaning? I've had this occur occasionally with cars. They didn't have ABS. Also airplanes. Did it occur around 53 mph?

dlmeyers 90 coupe zf6 3 speed shocks