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93 Camaro, completely stock. I just want to read the ABS codes for now.
ABS light comes on and goes out during startup. ABS INOP illuminates when the car starts moving (5mph) and stays on for the remainder of the drive. According to the service manual, "Low Trac" is supposed to come on and go off during initializing sequence. MINE DOES NOT. This car does not have traction control, but the service manual says this light comes on during ABS operation, and possibly during startup (V6) or on roll-forward (V8).
-I've checked connections at Front L/R wheel sensors, and rear diff sensor. Wiring is like new, just like the whole car, only 17k on it, no modifications. -Fuses and relays are both good. Replaced the relay just to be sure. -I've removed the driver's kick panel and made sure connectors are tight at EBCM, wiring looks factory fresh, I moved the harness a bit to put different tension on the wires. -If I disconnect EBCM and turn the key on, ABS Inop comes on, and stays on. So, it's doing "something" when it's plugged in, just not sure what. -Brake switch is functional -3rd brake lamp is unmodified, and two factory bulbs are both in working condition. -Brake lamps are in working condition -Parking brake works normally, "BRAKE" light on cluster is only illuminated briefly during startup, and when parking brake is set. Normal. -Grounds at radiator support/apron are clean/tight/look brand new.
I bought a very old Snap-On MT2500 with appropriate primary GM cartridge w/ ABS functions. Input all the correct parameters for engine and year, and it validates it's for a Delco/Delphi ABS VI system. No matter what I do, I can't get the damn thing to communicate with the ABS module to pull codes.
Questions:
Do I just assume the EBCM is dead, and replace it? Is there something about the scanner I'm just not getting? I even read the damn books. It came with a few different cartridges including one for through 1997, I used that one (presumably for the OBD II cars) and no dice. No communication. Communicating with the ECM works fine, absolutely beautiful. Also of note: I can't communicate with the airbag module. It has factory airbag and the light comes on and goes out like it's supposed to, no concerns with airbags other than I can't use the MT2500 to "connect" to it.
ABS was working like 100 miles ago. I wasn't paying attention to light sequences or anything. I used to hear the homing procedure or whatever it does when I'd start and roll, and the ABS INOP light would stay out while driving.
Other than starting to replace parts, I think I'm in over my head. I hate throwing parts at stuff just to eliminate my own lack of knowledge/understanding..
Normal operation is for the “LOW TRAC” light to come on when the ABS is activated (pulsing the pedal). Yes, same light that is used to indicate low traction on the TCS/ASR cars, but that wasn’t available until 1995 model year..
Don't know about the MT2500. We have a member here (GaryDoug) who has written scanning software (free download) for rhe OBD-1 LT1’s. It reads ABS codes and has bi-directional capabilities with the ABS actuators. Most people find this software extremely useful. Take a look and see if it might be useful:
Interesting that the MT2500 will not read the 93 air bag (SIR) system. Gary's program will not read early 93 SIR either. But as he notes there is an easy way pulling codes on the 93 SIR, outlined in the factory service manual.
Thanks Injuneer. It's been so long that I don't own a PC anymore, or a copy of windows so I could run it virtually on OS to use Gary's software. I should, but I don't.
The Snap-on Brick should work. At this point I'm thinking it's an issue with the EBCM itself. . Thought is, if I can get it to connect, then I can read any codes and focus my troubleshooting. If the new one is incommunicado too, then, I've wasted money and I've relegated myself to hours of testing connections, and the car will probably go to a shop anyway.
I don't understand enough about the connections and the symptoms that I'm seeing to know where to focus my attention. I've read probably almost every thread on this subject and I'm 200% certain my 3rd brake light is working, and/or the bulb in the cluster DOES NOT need to be pulled out to solve the problem. This is a classic car, and everything must work to spec.
The front sensors can fail internally, apparently from 25 years of dirt and corrosion (even if mileage is low). Rear sensor can accumulate metal particles that cause it to stop working. Checking the wires and connectors might not detect the problem
I don’t know a lot about the ABS, because I never had a problem with mine until I installed a Strange 12-bolt with their proprietary sensor. Sensor was not reliable. When I was able to help someone he had pulled the code (77) and I helped him work the way thru the manual logic diagram. Code was for the resistance of a circuit for a solenoid in the ABS motor pack. Logic diagram led to “faulty EBCM”, and replacing it solved the problem.
At this point, might be worth trying a brake shop, a GM dealer, or a friend with a GM Tech tool to see if they can connect and pull the code. The EBCM wire connects to the tan PCM serial data wire on pin M in the DLC. Maybe check the continuity of the wire from the EBCM to pin M.
The front sensors can fail internally, apparently from 25 years of dirt and corrosion (even if mileage is low). Rear sensor can accumulate metal particles that cause it to stop working. Checking the wires and connectors might not detect the problem
I don’t know a lot about the ABS, because I never had a problem with mine until I installed a Strange 12-bolt with their proprietary sensor. Sensor was not reliable. When I was able to help someone he had pulled the code (77) and I helped him work the way thru the manual logic diagram. Code was for the resistance of a circuit for a solenoid in the ABS motor pack. Logic diagram led to “faulty EBCM”, and replacing it solved the problem.
At this point, might be worth trying a brake shop, a GM dealer, or a friend with a GM Tech tool to see if they can connect and pull the code. The EBCM wire connects to the tan PCM serial data wire on pin M in the DLC. Maybe check the continuity of the wire from the EBCM to pin M.
Thank you. Yes, have the factory '93 service manual download (albeit for a Firebird) from that link. ABS is pretty much the same between the two. I'm taking a gamble on a reman ABS unit. Since buying the car, it first had a ABS INOP and "BRAKE" light on simultaneously, which resolved after replacing the battery (car had a completely dead battery after sitting for a while). Then, a few days after new batter was when the latest round of ABS INOP started. AT the very least it will enable me to rule out the EBCM to see if it behaves the same or different. If a $200 gamble on a reman EBCM doesn't fix it, then it's going to a dealer or shop because I bought the car to enjoy over the summer and the summer is going by quickly.
Originally Posted by moparman
Would using the OBDII cartridge in an OBDI car have an effect on what the scanner sees?
I've got the OBDI cartridges too, they all produce the same result, no communication with EBCM. I thought maybe the later VCI cartridge for the MT2500 would have the most recent updates and connect-ability, but none of them want to communicate.
New EBCM is still on its way. Until then I did some probing of connectors per the service manual. The only weird thing I found was terminal A11 on the 32-way EBCM connector. According to the service manual, with the ignition ON, and terminal A11 on the connector grounded, there should be less than 1 volt. I'm getting right about 5 volts. Service manual says repair short to voltage in circuit 800 which is the tan wire coming off the ECM that runs all around the front of the car through the forward light harness, and, under the dash. Screw that, I'll just get rid of the car...lol
I don't understand what the manual says about voltage and A11...its the serial data link. The ECM, EBCM, and SIR module all use this and report out at terminal M on the DLC. If the ignition is on I'd expect there to be communication/voltage, but the service manual says <1 volt. I've been told serial data runs at approximately 5 volts in everything else. With the ignition off, A11 to ground should be less than 2ohm resistance, and it is. So is this a typo/mess-up in the service manual?
After probing connectors and putting everything back together, two stupid-weird things are happening. One, the ABS INOP light is solid-on now when the key is turned on, and doesn't go off after 3 seconds like it used to. That, and my MT2500 brick scanner will no longer communicate with the ECM. However, the ECM will communicate with my Actron scanner just fine. All fuses and relays are still good. WHAT THE HELL this is driving me nuts.
I'll figure out it eventually. This one is just a bit over my head in terms of diagnostics. The car is in pristine shape and only has 17k miles now, so while not necessarily a "collector" car, it is all original, and the goal is to have everything working per factory spec (although, given the number of 'abs inop' threads on this site alone, I'm not sure ABS ever worked right from the factory on these cars!! lol)
Reman EBCM is in.
We're back to almost everything being good....Self-test, startup, initialize and flash the low trac light, all good.
Now.....
ABS light comes on and stays on when going down the road. Clears again at startup, repeat.
Snap-on scanner can communicate with the ECM again. This I can replicate. Plug in old EBCM, scanner can't see ECM. Plug in new EBCM, scanner can see ECM. Yes, that's correct, the old EBCM seems to mess up the serial data with the ECM.
FFFFFFFF I'm really starting to hate this car. I have to trust the reman EBCM is working and something else is causing the communication error, and there's something wrong higher up.
1. I still cannot get the EBCM to communicate. I've done all kinds of diagnostic tests, so it must be my scanner or something else wrong with the serial data bus (tan wire, connects also to ECM and Airbag DERM). Different problem for a different day.
2. ABS INOP light is OUT, and ABS is WORKING!!! This is with the new EBCM installed. I was getting successful initialization of the EBCM and ABS hydraulic pack, but the ABS INOP light would set anywhere from about 25-50mph and stay on. Restarting the car would reset the light until it was driven at speed again. The only unknown variable here was the brake switch input. Brakes and 3rd brake light all good, however, there's this HUGE connector next to the EBCM, C200 (b,c,d) where 3 different harnesses connect. This carries just about everything. As soon as I started unseating it (it bolts together) I saw the issue: The connector had been seated at an angle and the bolt driven in, cross-threaded. The most open part of the connection was......THE BRAKE SWITCH INPUT. I re-seated the connector and went for a drive, and just about cried tears of joy. The ABS INOP light stayed out. Restarted it, ran it up to speed, still out.
3. Somewhere in tearing into the car, I lost cruise control. I thought it might be related to ABS, but now that ABS is working, and cruise is still not working, I have a new problem. So now I get to go through the diagnostic process with the cruise control.
I almost started a new thread but this was in the ball park of my issue. I have 94 LT1 pretty damn stock except for wheels. The dreaded ABS INOP light is haunting me. I turn key on and it flashes as normal. Start car it goes out. I can back up and I hear a click sound under hood for brakes as if it some engages or switched EBCM motor? Normal I suspect? I put car in drive and light comes on and stays on. I do have 17x9.5 265/40r17 up front and 18x10.5 295/35r18 on back. Thought maybe that was issue but can't remember if that's exactly when this started since its been on a few years. I have not checked wheel sensors or connections to to EBCM or sensors. I bought usb cable from ALDL to began nosing around and have Scan9495 loaded. I can scan ECM without issues. Drove around and tired clicking ABS button to scan. It tries but turns back off and I get the below errors in comms. I can't read ABS module at all. My first thought is faulty EBCM or is there some config on ALDL cable needs set or some setupp in software? I notice ALDL cable had a jumper on usb side. Trying to get code read to troubleshoot but having issues reading EBCM but maybe EBCM is the issue. Any ideas?
Having just done the diagnosis on mine, it sounds like you have two different issues.
Issue 1 - If the circumference between front and rear tires is off, it will probably set a code. The fact that code only sets when the wheels are rolling but initializes successfully on startup hints that it's probably a sensor input issue. Not that the sensors are bad, but it is detecting different speeds between front and rear wheels. Swapping rear gears for a ratio other than stock will also cause issues because of the different speed output compared to what the EBCM is expecting.
Issue 2- The no communication issue could be a bad EBCM. There's a diagnostic-diagnosis flowchart in the service manual (searching here, there's a link to it) which will help you confirm that there is connectivity in the serial bus and the appropriate pieces are receiving power. But, me thinks even with a perfectly-functioning EBCM, you will still get the ABS inop light if there is a circumference difference front/rear.
Blue Streak sells reman EBCM's still. Mine was about $250 through Autozone. There are salvage/used options on Ebay but to have a known, working unit (and someone to call, if it didn't) made sense to me to spend the extra money.
Thanks Skookum. I plan on correcting wheel stagger and have same size on all four. With the scan I wasn't sure if I was doing something in correct with cable and software or not. Once I plug cable up ABS light stays on from start and doesn't go off. I never get any data. From comms is tries to connect but no reply and times out. I will check service manual for flowchart. Would like to confirm EBCM is bad before buying a reman.
I'm going to PM GaryDoug to see if he can take a look at the scan9495 communication issues. He seems to be absent from a couple forums we both follow. Might be vacation time.
07-21-2019, 04:55 PM
