ABS INOP and Brake light
10-25-2015, 07:29 AM
#1
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ABS INOP and Brake light
1994 Z28, M6
I have read several good threads on this issue here but could use a little more advice.
I had been having intermittent ABS INOP until a couple days ago but now I have a constant ABS INOP light as well as a BRAKE light. Brakes are fine otherwise, fluid is full, no leaks so I don't think the BRAKE light is related to brake circuit pressure differential.
So I suspect the problem is the ABS electronic module as my first guess, then the main ABS hydraulic/motor unit as my second guess. Oh, I tested the e-brake switch to see if that was giving me the BRAKE light and it was working properly. And I tried another relay in the ABS socket and it didn't make a difference.
Anyone know how best to approach diagnosing? Since it is 1994 and OBD-1 I am not sure there are any brakes codes available.
I have read several good threads on this issue here but could use a little more advice.
I had been having intermittent ABS INOP until a couple days ago but now I have a constant ABS INOP light as well as a BRAKE light. Brakes are fine otherwise, fluid is full, no leaks so I don't think the BRAKE light is related to brake circuit pressure differential.
So I suspect the problem is the ABS electronic module as my first guess, then the main ABS hydraulic/motor unit as my second guess. Oh, I tested the e-brake switch to see if that was giving me the BRAKE light and it was working properly. And I tried another relay in the ABS socket and it didn't make a difference.
Anyone know how best to approach diagnosing? Since it is 1994 and OBD-1 I am not sure there are any brakes codes available.
Last edited by Raylo32; 10-25-2015 at 07:48 AM.
10-25-2015, 08:18 AM
#2
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Re: ABS INOP and Brake light
Download a free copy of Scan9495. Build or buy a cable to connect to a PC. Read the ABS codes. Look them up in a free download of the 1994 factory service manual, or one of us will look the up for you.
Much easier than guessing.
https://www.camaroz28.com/forums/com...95-lt1-874306/
LINK: 4TH GEN SERVICE MANUALS - Firebird Nation
Much easier than guessing.
https://www.camaroz28.com/forums/com...95-lt1-874306/
LINK: 4TH GEN SERVICE MANUALS - Firebird Nation
10-25-2015, 08:31 AM
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Re: ABS INOP and Brake light
Sounds good, I'll give it a try. I already have a cable for TTS Datamaster... but I haven't been able to transfer my license for it to my latest laptop. I need to follow up with them again... but if the free scan program you referred to works with my cable that will be even better.
10-25-2015, 09:06 AM
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Re: ABS INOP and Brake light
I'll ask the author of Scan9495 if he thinks the Datamaster cable will work.
10-25-2015, 09:18 AM
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Re: ABS INOP and Brake light
It should work. Datamaster works on the cables I use for Scan9495. I am not really familiar with the Datamaster cable, but I doubt there is anything proprietary about it.
10-25-2015, 10:40 AM
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Re: ABS INOP and Brake light
Well, it's "fixed".
After 3 days of steady ABS and BRAKE lights they just went out. I did a 3 leg errand run, on the first leg running TTS Datamaster (luckily I can do a few trial runs until I get my license renewed). TTS reported zero DTCs. I drove to the second location, lights still on. Then leaving there the lights were off. So I immediately set about testing with some hard stops and ABS worked properly and I got the LOW TRAC light.
Who knows if it'll work the next time I get in the car??
I have another minor electrical gremlin I've been chasing... the LOW COOLANT warning. It comes on and goes off at random. Radiator is full, reservoir at proper level. I even replaced the level sensor in the radiator, no change. Low coolant light comes and goes. Temps are normal at all times. Another mystery.
After 3 days of steady ABS and BRAKE lights they just went out. I did a 3 leg errand run, on the first leg running TTS Datamaster (luckily I can do a few trial runs until I get my license renewed). TTS reported zero DTCs. I drove to the second location, lights still on. Then leaving there the lights were off. So I immediately set about testing with some hard stops and ABS worked properly and I got the LOW TRAC light.
Who knows if it'll work the next time I get in the car??
I have another minor electrical gremlin I've been chasing... the LOW COOLANT warning. It comes on and goes off at random. Radiator is full, reservoir at proper level. I even replaced the level sensor in the radiator, no change. Low coolant light comes and goes. Temps are normal at all times. Another mystery.
10-25-2015, 12:29 PM
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Re: ABS INOP and Brake light
The code(s) that turned on the ABS INOP light are still stored in the EBCM system. Datamaster can't read those. Scan9495 can.
10-25-2015, 12:52 PM
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Re: ABS INOP and Brake light
It sounds like the wiring or connector is shorting to ground intermittently. Either that or the latching module (or retained accessory power module) is defective.
10-25-2015, 01:31 PM
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Re: ABS INOP and Brake light
I just downloaded the LT1 version of scan9495 and it works fine with my Datamaster cable. Nice program, GaryDoug! But there were no ABS DTCs live or stored. I didn't see a specific place to look for stored codes. On the ABS tab is simply said no DTCs.
I guess all this action has me a little relieved. Having the intermittent ABS INOP I figured I have a sensor dirty or going bad. But it could just as easily be the ABS electronic module glitching, I suppose. But I was happy that when the lights cleared the ABS worked so hopefully the $$ hydraulic unit is not the problem.
I guess all this action has me a little relieved. Having the intermittent ABS INOP I figured I have a sensor dirty or going bad. But it could just as easily be the ABS electronic module glitching, I suppose. But I was happy that when the lights cleared the ABS worked so hopefully the $$ hydraulic unit is not the problem.
Last edited by Raylo32; 10-25-2015 at 01:33 PM.
10-25-2015, 03:33 PM
#10
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Re: ABS INOP and Brake light
Unfortunately Scan9495 does not presently read ABS history codes. You would have to wait until you see the current codes accompanying the ABS INOP lamp. I can probably add the history code feature but it will take at least a week do do so.
10-25-2015, 11:21 PM
#11
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Re: ABS INOP and Brake light
I had to come in here just for kicks.You mentioned you checked the emergency brake light switch,but I bet it's the brake light switch under the dash.When I had this problem with my old bird,that's what it was.Paid $150.00 for this fix.You have to be a catorchionist (spelling check) to get up in there.Just follow the brake peddle and turn right you can see the wires.Good luck.I made sure my third brake light socket and bulb were correct and working.The third brake light is wired to the abs system( you can see this on a diagram)The correct bulb is important.#921 on the 93.On the coolant issue do you have a lot of rust in your radiator?Might be clogged.Also you can loose coolant with a Stant radiator cap and or hoses not real tight.Might use a GM cap.Are you sure the radiator is full when cold and you are running 50/50 green stuff?The coolant sensor can become corroded and might have to be cleaned.Whew.(brake light switch at rock auto is $10.00) Hope this helps.My02
10-26-2015, 07:45 AM
#12
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Re: ABS INOP and Brake light
Well, it didn't take long for the ABS INOP light to reappear... happened this AM on my startup to drive to work. But the BRAKE warning light is out so it looks like I am back to my intermittent ABS INOP situation, probably caused by a dirty or failing wheel or axle sensor. Hopefully scan9495 will help me diagnose, but I need to have the laptop in the car ready to go when the light is on since it doesn't read stored ABS codes. And I wonder, if my assumption is correct that I have a sensor going out does scan9495 have the ability to identify which one is not communicating?
10-26-2015, 10:12 AM
#13
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Re: ABS INOP and Brake light
I just read the thread below on troubleshooting ABS INOP. That confirms that scan9495 does report individual sensor issues. The thread also gave some detailed troubleshooting procedures and measurements. So with that I have enough info to proceed. I'll post the results here.
10-27-2015, 04:09 PM
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Re: ABS INOP and Brake light
After 3 days of driving around it is safe to say I am back to the old intermittent ABS INOP and no BRAKE warning lamp. I carried the computer with me until I got the ABS INOP then booted up scan9495 and got ABS DTC #66. From the thread below I have the diagnostic path forward. Looking less like the sensor as it continued to show normal wheel speed info all along. So looking like a wire short or more likely a bad rear ABS motor. Damn....
=============================================
DTC 66 Rear ABS motor circuit shorted to batt
Occur either on short to batt or low/no resistance in abs motor when ECBM turned off. Diagnostic tree is check wiring for short, check abs motor pack for internal short, check ECBM.
Good news is it does not require tech tool to diagnose, only a multimeter. Add an email address and I will scan the pages from the manual and send them to you.
=============================================
DTC 66 Rear ABS motor circuit shorted to batt
Occur either on short to batt or low/no resistance in abs motor when ECBM turned off. Diagnostic tree is check wiring for short, check abs motor pack for internal short, check ECBM.
Good news is it does not require tech tool to diagnose, only a multimeter. Add an email address and I will scan the pages from the manual and send them to you.
Last edited by Raylo32; 10-27-2015 at 04:17 PM.
11-07-2015, 09:48 AM
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Re: ABS INOP and Brake light
Well, not knowing the pinouts to test the wiring... and the improbable chance that I would be able to find in in the failed state, I decided to just replace the EBCM. That thing was a bit of PITA to wrangle out of its location. I got the replacement reman unit from Rock Auto, installed it, started it up and no ABS INOP light. And it hasn't come back over 2 days of driving (about 5 or 6 short hops). So calling it fixed.
I also replaced the coolant level sensor (again) and that light is gone, too, hopefully for good.
I guess I am getting the car ready to sell.... maybe going to get a C7 Vette or the new Camaro if it isn't as much of a coffin like the previous. The super high door sills and slit woindows were a deal breaker for me. Have to sit in the new one to tell if it is better. Or maybe even a new Shelby 350 with the flat plane crank. That looks intriguing. Or maybe even an ATS-V. We'll see.
I also replaced the coolant level sensor (again) and that light is gone, too, hopefully for good.
I guess I am getting the car ready to sell.... maybe going to get a C7 Vette or the new Camaro if it isn't as much of a coffin like the previous. The super high door sills and slit woindows were a deal breaker for me. Have to sit in the new one to tell if it is better. Or maybe even a new Shelby 350 with the flat plane crank. That looks intriguing. Or maybe even an ATS-V. We'll see.