I've had the ANTI-LOCK light on in my '89 coupe for several months now. I took the car into the dealer today, since nobody else could properly read the codes from the Bosch ABS unit. The dealer struggled with the troubleshooting process, but they finally came to the conclusion that the computer module was bad and that this requires a replacement of the EBCM. Though they say it's the computer module that went bad, it will require the replacement of the entire system (ABS pump AND the module) since they come as a package deal.

The fact that it needs to be done isn't so bad -- what really frustrated me was their price for doing so. They want $1400 for the job. $1100 of it is for the EBCM unit, the rest is labor.

I did some hunting around (i.e. gmpartdirect.com) and found that I can get the module, new from GM, for about $650. How's that for my dealer screwin' its customer? :eek: I'll bet I can get a salvage unit for lots less too.

Anyway, I'm wondering if I should tackle this project myself. My mechanics experience level is about a 2 on a 10 scale.

Is this a difficult project? Any major gotchas?

Has anybody else had to replace their EBCM IN AN '89 COUPE? (I specify an '89 since the '89 ABS units are different than most other year C4's). If so, do you have a story to tell about it?

 

I'm not a "auto" mechanic, but if you feel confident. Disconnect the battery before removal. The computer runs a self test so you shouldn't need any test equipment

 

Hello again,

I have a 90 and spent about 40 hours working ABS EBCM issues.

Some anecdotal comments. When I finally narrowed down the trouble shooting process to the Electronic Brake Control Module (EBCM), I balked at $1100 wholesale (90). Found a used module, pump, all relays, for a whopping $160 plus shipping. They accidentally sent a module for the 89 but quickly corrected the problem. You do not have to replace both unless both are bad. The module came out of the 90 in about 15 minutes. The 89 looks identical to the 90 however the part number is what tipped me off. It even plugs in the same, same brackets. I actually installed the 89 module in the 90 thinking maybe the parts book was wrong. Oh well. What is another 15 of Corvette time. Maybe different location in the 89 but SERIOUSLY doubt it. Look behind the drivers seat, ABS compartement, shinney little box forward of the pump, big connector on top. Two bolts, two snaps for the wire harness. Pretty darn sure the 89 and 90 are very close. It's been 18-24 months since completing the job so may have missed a few things.

I would consider a used system. Some salvage places will sell just the module. Try Ebay -"ABS Computer" or "Corvette ABS", along those lines. If that fails, let me know and I will try to find the Email address for the guy who sent me the Model Year (MY) 89 ABS EBCM. I will also provide the part number if you like. I wouldn't spend that much money, cause I suspect they are guessing. My used module still works. Those systems are quite reliable and should be available. Guys parting out the 86-89 would likely offer some good deals. I am nearly certain the 86-89 part numbers are the same. Let me know if you want more help.

dlmeyers 90 coupe zf6 3 speed shocks




[Modified by dlmeyers, 12:06 PM 7/29/2003]

 

Excellent insight David, thank you. One of the first things I did yesterday, after receiving the bad news from the dealer, was initiate a search at local salvage yards for a used unit. Nothing found yet.

Yesterday evening, I went into the back compartment and looked (again) at the system. Everything you describe, including the location of the module itself, is exactly correct. I originally spotted the selective ride control module and thought IT was the ABS module, but now I realize that it's the aluminum-boxed unit that's forward of the ABS pump.

I have the part number (not right here with me, unfortunately, or I would give it here) -- the dealer gave it to me after the diagnosis. I did find a part number on the web for it: 14103343. I'll check at home later to see if the dealer-provided # agrees.

Please give me the email address of the person from whom you purchased the used unit from. I'd like to find out if they have what I need in stock. So far, I have been unable to locate a source for a used unit. gmpartsdirect.com offers it for about $650, but I much prefer to get JUST the module and not the pump too (it's probably not needed).

 

Sent the Instant Message with his address.

Don't recall your ABS symptoms. Should you get some time, would like to hear about the light, when it comes on, if it goes out before the car moves, things like that. Long time ago found a copy of the Service Technology ABS training book. It was for the 90 but very similar to the 89. It may help.

dlmeyers 90 coupe zf6 3 speed shocks

 

I had the same problem with my 89 when I bought it... had the dealer diagnose the computer as the cause and bought a used one on ebay for $40.00 and the ABS system works like a charm. Call VetteMasters at (757) 575-8715. They are in virginia beach, VA and that's where I got my computer. He had a large number of them and gave me a 6 month warranty.

Skip

 

I found a salvaged computer module at a local Corvette salvage yard yesterday afternoon. I installed it last night (incredibly easy installation, BTW), and found that it did not fix my problem. Either the salvaged unit is bad, or my problem is not the computer module (likely it's the latter).

I noticed, with either the old or the new computer module, that when I turn the ignition to the "ON" position, there is an awful lot of clicking going on with the relays. Now, I don't know what's considered "normal" for the amount of relay clicking, but there was what I would consider an abnormal amount of clicking. It sounded almost as if one of the relays was going "nuts" for about 3 seconds.

It's definitely guesswork, but I'm wondering if the problem lies in one of the relays. I hate the notion of "throwing parts" at a problem, but I'm tempted to replace all 3 relays (the control module relay, and the two relays that plug into the top of the pump housing). I'm pricing out these relays now, and if they aren't too outrageous in price, I will replace them and see what happens. I figure all 3 relays should be under $200 if I can acquire them thru a friend who can get a discount from the dealer
:cool:

It's coming down to a gamble of whether throwing some money at stuff like a salvaged module and new relays is going to fix the problem. I'd say the gamble has pretty good odds for me, considering the dealer wants $1400 to replace the entire ABS system. I'll post here later when/if some progress is made.

 

The Symptoms

The problem has existed since I bought the car several months ago. 99% of the time, when I start the car, the ANTI-LOCK light comes on immediately, and stays on for the duration of the ride. Specifically, when the ignition is turned to "ON", it performs its self-test and fails that test within a few seconds and turns on the ANTI-LOCK light on the DIC.

Every once in a while, not often though, the self-test is successful and the ANTI-LOCK light stays off. As I begin to move for the first time, I will hear the ABS pump do its cycling, so I know the ABS pump is working ok. I will drive for typically about 10-15 minutes and then the system will "wig out" for a few seconds then the ANTI-LOCK light will come on. All bets are off, at that point, as the ABS system has taken itself offline. Usually when this happens, it occurs after I have come to a stop at traffic light. At a complete stop (still with the ANTI-LOCK light off) the brake pedal will pulse and the "ABS ACTIVE" light comes on. This will occur for about 3-5 seconds, then the system takes itself offline.

 

The symptoms you describe suggest a bad OVP relay.

With key on, engine off, the light should be on, but only for a moment or two. Not sure about what light display you have but the system goes like this. With key on, power heads for the OVP, with OVP relay powered, current flows to the module, fires up the circuits and gets ready for work. The first thing on the list is to turn OFF the DIC light. With no module power, the light will stay illumintated. The first clue. I suspect the clicking is the relay pulling in and out. It may explain when it did work occasionally, the relay would fail, and quit again. The module then waits for the BIT check, pump relay, pump operation checks, etc.

If I had to make a bet, beer of course, I would start with the OVP relay. As you stated, replacing all relays will cost some but far less than dealer repair. Consider going back to the yard and buying used relays. Then again, for around $125, I think you can buy all three relays. I have the relay tester from Gordon K. Wish you lived in the area. You can check those with multimeter and power source, or just replace the darn things. And yes, I too hate throwing parts at systems. That said, if you plan on keeping the car, replacing 14 year old relays, not exactly wasteful. Close, but who knows how long they may be available. Oh well.

Let us know how this turns out. You would be the second case of the OVP relay failure noted within the last six months. Your symptoms were almost exactly like those noted on another list. Plus I just reviewed the Service Technology book and pretty darn sure the relay(s) are the culprit. I am excited.

Darn cars.

dlmeyers 90 coupe zf6 3 speed shocks


[Modified by dlmeyers, 11:20 AM 7/30/2003]

 

Which of the 3 relays is the "OVP" relay?

In my case, the ANTI-LOCK light lights up on initial key-on (I suspect this is for the purpose of bulb-testing), then it goes off. Then, within a couple seconds, it comes back on.

If the relay fixes my problem, I'll be shipping a six-pack your way :cheers:

I'm a closet electronics technician (actually, I'm a ham radio operator who loves to tinker and build my own equipment), so it crossed my mind to whip out the multimeter and mess with the relays. But, then it also occured to me to replace them anyways ... I plan to keep the car for a L O N G time, so anything that gets fixed gets fixed with longevity in mind. So, replacement will be the way to go.

I, too, am starting to get excited about where this is going. I've fired off an email to my buddy who can get a substantial discount at a local dealer, so that I can get a hold of some replacement relays. Not sure yet (until I see your reply) which one of the three is the "OVP" relay, but I'll replace all three nevertheless.

Darn cars. ;)

 

I have the same problem since my stereo was installed, Wished I would have taken Pix of the owners face today when I went in with the receipt and estimate for the repair. $2200 of which $1680 is for new Valve Modulator Assy, and $175 is for the troubleshooting. Here is what I have found out:
I had to go to a Buick Dealer to get mine troubleshot. I talked with the mechanic when I picked it up, I had a Code 63 Valve Modulator Relay assy. This is hte one that allows power to go to ground and activate the ABs. If it is bad, then ABS light will stay on at Power on. The relay was good (tested good) and using the breakout box it has been determined that I have an open from Pin 8 on the modulator valve to ground. The ground circuit from the Modulator Assy to actual ground was good. So what appears to have happened is that the connection inside has gone bad. From the schematic it goes from the relay to the Chassis case. We are currently looking for a Valve Modulator Assy from anywhere but the dealer as th ebest price we can get on a new one is around $900 to the door.
This annoyed us too! Looking at it, It appears to be a black plastic box the relays sit on, a harness plugs into, and wires go out to control the valve motors. If we can't get a good deal on a used one, we are going to try and open the box as we cant break something worse that is already broken. Hopefully the schematics are true and there is just a wire there.
I think mine was $861 at gm parts direct.com, the local Chevy Dealer will get me a new one at $900, there actual cost was $840 or so.
Actually by referencing the part number for the valve assembly(different than the EBCM) 86-91 are the same. Not sure if this holds true for the EBCM though.
What code(s) did they tell you you were getting? The deal about them being one unit is BS. They are 2 unique and seperately replaceable units, if they read the manual they would see that! I had to go to the dealer to get mine done as my code was one of the four ABS codes that require a Tech 1. If you get a good deal on a complete assembly shoot me a line as I need the Valve Modulator!

Sharing my $.02 for what it is worth

Doug

 

I am not familiar with a "valve modulator". Is that part of the ABS pump? Or, are they one and the same?

My dealer told me they were unable to get any codes from the ABS system, and that the reason why was because the control module was bad. I've since replaced the control module, and still no ABS system. So, I'm beginning to wonder if my dealer was simply unskilled with this system but didn't want to admit it :confused:

 

Yes the valve modulator is the "pump". If you have ABS light on you should have codes. The Chevy Dealer wont be working on my brakes again. I think the same as you as far as their skill with the brakes. What really bugged me was there excuse about not having the connectors and breakout box, when the Buick dealer had the tools, and called Chevy to get the manuals.

Doug

 

You guys are being fed a load of crap by the dealers. I was having trouble with my ABS system on my 90 and tracked the problem to what I thought was the EBCM. I went to the junk yard bought another ECBM and plugged it in. ABS light still on. I can't remember if it was the same fault code or not. In any event I replaced the ECBM with the original one and brought it to the dealer. They found a bad accelerometer. I don't remember if there is a code for that. I asked the technician about the ECBM I bought and could I use it as a spare. He said no problem, all he had to do was clear the code stored in memory. 99% of the time its a wheel sensor code because the car was involved in an accident. He cleared the memory and when I got home I swapped out the ECBM's to see if would work. It worked fine. The motto is:
DON't BELIEVE WHAT YOUR DEALER TELLS YOU. I was lucky because I went to the garage to talk to the tecgnician, not the service manager. :nono: :nono: :nono:

 

Here is a little more on my story...
When I bought my 89 the ABS light was lit. I took it to a local chevy dealer and they said the pump module was bad (something about a dump valve) and it would be $1200. I knew I was in trouble with them because the service manager pulled the car part way out of their drive in service area and walked back to me to ask how to release the parking brake. :crazy: Well, I called another checy dealer that has a separate corvette shop and talked to their corvette tech... he said that the Bosch pump units are bulletproof and last forever. I took the car to him and they can unplug the ABS computer and plug in a test computer to run the system through it's paces. He said that everything worked great and the computer was therefore at fault. Cost me $120 for diagnostics and $40.00 for the replacement computer. I'd try getting hold of a good GM dealer and let them diagnose the problem. Simply reading codes will not work... that would have had me spending $1200 for a pump module that I did not need... and still replacing the computer. These systems must be had for some to figure out because the guy I bought the car from had two receipts from dealers to fix the ABS system but were never sucessfull. He was eventually told that the 89 ABS was unreliable and to drive with the light on. :confused:

 

OK, let's sort this out.

First, the OVP is the OverVoltage Protection Relay. Should be the relay off to the side of the EBCM, towards the centerline.

The second relay, "Pump Motor Relay", the forward relay mounted on the pump assembly. The "Solenoid Relay" aft mounted relay described as part of the modulator valve. The modulator valve and pump assembly, I consider a unit. Beleive they are NOT field serviceable. These are tested during the rolling check.

The 86-89 EBCM should have the same part number. This was the first EBCM unit, and unfortunately, it didn't store/allow code retrieval. Troubleshooting the system required an ABS test set. Can't find my Kent Moore book for the number but this test set was the size of a filing cabinet. Very expensive, and have actually seen one on EBAY. I almost bid. Then reason set it. You can do a lot of testing with a good multimeter and I have a 90. The 86-91 has the same pump assembly, as noted in earlier post. In 92, Acceleration Slip Regulation (ASR) became a reality resulting in new pump/module/valve parts.

The 90 allowed for code set and recovery. The 90/91 EBCM MAY be the same part number. NOT SURE. The 90 modules were manufactured in both Germany and the US, same part number. You can retrieve codes with the plug, a tech 1A, or Snap on scanner. When you buy a salvage EBCM, it may carry a code from the crashed vehicle. Plan to reset immediately upon installation. You can trouble shoot with a pin out box J35592. May be able to use this on 86-89. Don't have the manual for that year.

You say the light goes out, then comes back on almost immediately. Hmmmm, a new fact. Well, like I said, with relays clicking etc, I still like the relay guess. Maybe. The salvage yard will likely sell you the relay, cheap. It is not part of the pump assembly per se so they may let the OVP go.
They will likely NOT pull the pump/solenoid relays off a complete pump assembly.

About the dealer. Any dealer saying an 89's EBCM is bad 'cause no codes, well, better refer them to the manual, assuming they have one. No codes on 86-89. Beware of any advice or purchase decisions based on their opinion.

The EBCM does several tests during different times. Based on the schematics, there is a voltage feed back loop from the pump and modulator valve assembly. I suspect the EBCM uses this as part of the BITE check.

At any rate, the accelerometer switch (90 and above had the sensor)could also be a problem but don't see how this could cause the relay clicking, but ya never know. I reserve the right to be dead wrong.

For further reading, see STG publication #15005.08-1 (86-89), #15005.08-2, or 13003.02-1 (ABS/ASR)

Keep us informed. (And Hello Larry)

dlmeyers 90 coupe zf6 3 speed shocks

[Modified by dlmeyers, 8:00 PM 7/30/2003]


[Modified by dlmeyers, 8:02 PM 7/30/2003]

 

DUDE, If you read my post.......you would see that I troubleshot this and I DID TALK TO THE TECHNICIAN!!!!! I work on my Vette until it is something I cant fix. In my case I had one of the (how many are there for the ABS that dont report unless you have a Tech1?) codes that doesnt report through normal measures.(A:Four codes) I usually talk to the tech before they even work on my car, I have asked to have other techs work on my car after talking to some of them, and I ALWAYS talk to the tech who worked on my car afterwards. :rant:

 

Looking at the schematic and the module, the relay sits in a socket that appears to be a black plastic box sitting on the 2 valve motors. There is a harness that plugs in right next to the relay. According to the troubleshooting done with the breakout box, I am open from the relay (Pin 86 i think it is) to ground. THe circuit fronm the case to ground (CKT150?) is good, so therefore logic says that I am open from the relay to the case ground. The relay doesn't activate, as this circuit is for the coil that energizes/activates the relay(I dont remember off the top of my head but I believe it is Normally Open). So Inspecting the little black box, it appears as if it can be opened. I found a used modulator today for about $100, so will probably drop that one in. Either way, If I try and repair it, what is the worse that can happen? I break something that is already not working? Looking at the schematic it appears to be a straight shot from the relay to the case ground. The Tech that worked on my car wasn't familiar with Vette's as it was a Buick Dealership, but he was very knowledgeable on the Bosch ABS unit.
Does the Snap On require anything special to access the ABS? Or does it just require the ALDL CNX and the Normal Diagnostic Cartridge? Anyone have a schematic for the J35592, or one they are willing to open and take pics of? I told the Buick Service Manager I would buy one of his and one of his Tech 1A's he had laying around in back, he is still tossing it around.

[QUOTE}For further reading, see STG publication #15005.08-1 (86-89), #15005.08-2, or 13003.02-1 (ABS/ASR)[/QUOTE]
Where does one find this reading material?

Thanks,
Doug


[Modified by Dougs 90, 9:49 PM 7/30/2003]

 

In my quest to fix my problem, I found a good article on how to test the relays:

http://www.corvettefever.com/howto/19239/

 

Cool :cool:
Thanks
Doug
Good Luck to you with yours! :cheers: