Maybe not easy but I noticed a thread called "Easy Question" got a butt load of views and the original thread I had only got 69 so here goes...

For such a simple system, this ABS is kicking my butt. I got the car about a month ago and has had the Service ABS light come on every time I drive it. Sometimes within the first mile and sometimes after a few miles. I pulled the codes and it has the three listed in the title. It may have more but I understand it can only hold three at any one time. I have cleared the codes multiple times and all three codes eventually come back. The startup self test runs, I hear the pump and feel the brakes when I start off. No ABS light ever after the startup test. Tested the accelerometer. 2.7 volts on level ground. When I rotate it the voltage changes to 5.0 volts in one direction and .5 volts in the other. Will assume that is good. Haven't seen that written on a Corvette site but did see those voltages written on a Porsche site that said they used an early model Bosch ABS system.

I'll start with Code 21 - Have tested the RF sensor and it shows 1140 ohms. Went back to the body harness connector and measure resistance there and got the same. Went to the EBCM connector and measure the circuit and got the same. Wires are good. Not shorted to ground or power and the sensor shows good resistence.

Code 32 and 36 - Have verified the wires are good all the way back to the EBCM connector. Bearings are not bad on either side. Toothed wheels are clean on both sides. Pulled the sensor and cleaned them (they were both dirty around the magnets). Cleaned the sensor seating surfaces and reseated the sensors with sealant and 86 in lbs of torque. Still set the codes. Jacked the rear and put it on jack stands. Ran it in first gear up to about 12-13 mph(I don't recommend doing this but I'm desperate). Measured .80-.85VAC on the left side and .95-1.0VAC on the right. Put a piece of paper between the sensor and hub to increase the air gap and decrease the signal level on the right side. Got them within .05VAC. Codes still set again after I cleared them. Not sure what the air gap between the sensor and the toothed wheel is supposed to be. If anyone has an idea or knows what the signal level is supposed to be at a given speed, I'd like to write that in my FSM.

Only thing I cannot do is check the ECBM wheel speeds since I don't have a Tech1/1A. I have TunerPro v5 and ALDL to USB cable but haven't been able to establish comms with the EBCM using it.

Only thing I can think is the EBCM is flakey but I haven't read anyone having problems like this. Any other ideas?

Mike

 

Sounds like your doing better than most with trouble shooting.
There is little info found to assist trouble shooting ABS with the C4.
Your best bet is purchase a 91 FSM and find any ABS supplements if they exist.

 

Some good information here, hope it helps.

http://www.corvetteactioncenter.com/...l#.UiDU_D8SYs8

 

Have the FSM but not the ABS Supplement. Guess I'll go get one.

toptechx6 - I have reviewed the link also. That's where I got the idea to read AC voltage on the sensor lines. Definitely good information in the write up. It's for an earlier version but most of it still applies. In question are the voltages he reads while driving 15mph. I would like to know if htey are the same for the 90-91 ABS systems.

Mike

 

You're correct to look at the Porsche for some info...

They used the exact same system as did Mercedes, back in the day. I hear that MB or Porsche shops might have some manuals and other "stuff" from that era. If they kept it..

beyond that, if the codes are consistent and ongoing, if the sensor pathways are all proven good then its time to look at the module itself. Not a lot of info on that BUT, you CAN score replacements on FleaBay at decent cost. Just a PITA to install/swap.

I had some random ABS issues for a while. Flushed the fluid and cleaned the system and it "self corrected" the problem. Only other incident was a sensor tip knocked off...that set codes instantly at self test time.

Good luck

 

leesvet - Thanks for the encouragement. I haven't flushed the lines with new fluid but it is on my short list of things to do. That and the clutch fluid. I'll keep my eyes open for an EBCM. You can never have too many spares on hand anyhow.

 

A Tech 1/2 would be helpful in flushing the lines in the EBCM if you could get your hands on one.

 

Ok. ABS is fixed. Tore apart the plenum to get to the ground. Much easier this time but trashed the gaskets so had to wait for them to get the top end back together. While I waited, I pulled the halo and checked grounds on both driver and passenger side. Both looked new as did the one on top of the bell housing. Checked all the ABS sensors again because I had the time. Check all the ground for the ABS and Ride Control because I was there. Everything was as it should have been. Less than 1 ohm resistance for all ground circuits and ABS sensors were in accordance with the FSM.

Once the motor was back together I had also received the Tech 1A and ABS adapter. Hooked it up and ran the ABS auto test and it passed. Cleared the 32 and 36 codes I had from before and ran it in monitor mode. Right Front had no speed signal. I know the sensor is good because I tested it. So I run it again to show the wife. After the power cycle now both the front sesnors show no speed. Too many wierd symptoms so I replaced the ABS computer with one I bought last weekend that also arrived while I was waiting for gaskets and bam. Passed auto test, no ABS lights, speed signals were all there and the best test I could think of passed - slammed on the brakes, the ABS Active light was bright and pretty and the ABS actually worked.


Figure I still saved money after getting all the tools, spares and Tech1A over taking it in for repair. And I like new tools.

 

Congratulations!