SOLVED! Can't Scan for ABS Code

[Dadwagon]

My 4.2 Buick has been throwing up a random ABS/Brake light CHECK BRAKE SYSTEM warning for the last two months. After trying a couple easy fixes, I realized I needed to scan for the code. My cheap OBD2 scanner wouldn't do ABS "C" codes, so I bought an ELM327 reader and used iOS phone apps. None of the apps are finding any of the "C#####" ABS codes, or any Check Engine Light codes at all. It's driving me nuts having ABS turn off every once in a while, and I want to figure out what is throwing up the ABS fault and fix it.

Has anyone gotten a ELM327 and phone app to properly find a brake system/ABS fault code?

 

[Dadwagon]

And if you haven't, did you resort to a Innova reader? I'm trying to avoid another $99 purchase that doesn't do the job.

 

[Mooseman]

Unfortunately, iOS apps are junk. You'd have to go to an Android device and get the Car Gauge Pro app.

 

[TJBaker57]

My 4.2 Buick has been throwing up a random ABS/Brake light CHECK BRAKE SYSTEM warning for the last two months. After trying a couple easy fixes, I realized I needed to scan for the code. My cheap OBD2 scanner wouldn't do ABS "C" codes, so I bought an ELM327 reader and used iOS phone apps. None of the apps are finding any of the "C#####" ABS codes, or any Check Engine Light codes at all. It's driving me nuts having ABS turn off every once in a while, and I want to figure out what is throwing up the ABS fault and fix it.

Has anyone gotten a ELM327 and phone app to properly find a brake system/ABS fault code?

I am not at all familiar with iOS but if there is a serial terminal app for it I could walk you through the commands needed to pull those codes and how to interpret the result, as long as it's an older (before 2008) model. It would be a hands-on sort of thing, not a canned app doing the talking for you. Interested?

 

[Dadwagon]

Is Car Guage Pro the only one thus far that is proven to see the "hidden" ABS codes?

I'll look into a serial terminal app for the apple phones.

The winds seem to blow toward an Innova scanner

 

[TJBaker57]

Is Car Guage Pro the only one thus far that is proven to see the "hidden" ABS codes?

I'll look into a serial terminal app for the apple phones.

The winds seem to blow toward an Innova scanner

Have a look at Car Scanner for iPhone. The android version has a terminal screen. If the iPhone version does also that could be the way in.

The issue is that most of the app designers only included translation coding for the ECMs and PCMs... Torque even gets the results of the 'hidden' codes as you call them but it ignores them!

It is a simple matter of knowing the language. Once connected in a terminal app I can simply enter...

AT SH 6C 29 F1
19 FF FF 00

..... And that right there will yield all that the EBCM has as far as codes, current, pending, history, old, whatever. It won't be recognizable to most but I know what it means thanks to a very old post that got me started on it. I have a spreadsheet to make it even easier.

 

[Dadwagon]

Car Scanner is one of the apps I put on the phone. It does indeed have Terminal built in, accessed via Settings.

 

[TJBaker57]

Car Scanner is one of the apps I put on the phone. It does indeed have Terminal built in, accessed via Settings.

OK then!! If you connect to your ELM327 and can enter the following lines separately it should spit back a block of hexadecimal text that we can decode to get the codes. Lines that begin with AT are just instructions for the ELM327, not sent to the vehicle. After each of those the ELM should answer "OK". After the final line there will be a block of text. If you can screenshot that we can sort it out and have your code(s). There's a thread here that goes into detail but to just cut to the chase you could just try this. Also,,, after reading the codes typing the single command "14" without the quotes clears the codes from the EBCM while not affecting any other module of the truck.

AT D
AT AL
AT S1
AT H1
AT SH 6C 29 F1
19 92 FF 00

 

[Dadwagon]

I have a commute, baby duty, and chores today. Will try to get an hour and work on this project late tonight. Thank you all very much!

 

[TJBaker57]

I have a commute, baby duty, and chores today. Will try to get an hour and work on this project late tonight. Thank you all very much!

Here is a youtube demonstration I just made of the above mentioned code reading. Shows I have 2 history codes... C0267 and C0291

 

[Dadwagon]

Here is the output:

 

[Reprise]

AT D
AT AL
AT S1
AT H1
AT SH 6C 29 F1
19 92 FF 00

Sorry to hijack, but holy crap, this brings back memories.

 

[TJBaker57]

Sorry to hijack, but holy crap, this brings back memories.

Doesn't it!? I wish the ELM327 allowed for command strings like we used to use for modem initializations. The ELM327 only does single commands, but some things can be set in programable parameters.

 

[TJBaker57]

Here is the output:

Good work! I see a C0298, a C0292, and a C0265, all history codes. There may be freeze frame data for these but I don't think it would be helpful in this situation.

 

[Dadwagon]

Right on! Thank you very much, TJ!! Let’s see what those codes are...guessing wheel bearing

 

[TJBaker57]

Looking back at this I was a little remiss in instructions. The command atring I gave you only asked for codes that had fequested the MIL light, history codes, and current codes. While it is good to know what you have in that regard, and that is the exact same status that the tech 2 asks for, I would also want to look for pending codes and old codes just to see what may be currently happening (pending) as well as what has happened in the past.

To add pending and old codes to the request the final line would be " 19 F2 FF 00 ". Or to see everything except immature codes you send " 19 FE FF 00 " All the preceeding lines would be the same.

 

[Dadwagon]

Based on those chassis codes, it appears the ebcm needs to be removed and resoldered. Or a replacement sourced at a junk yard. Seeing as the abs/ brake light popped up today the second I plugged in my phone charger, it does appear electrical in nature. Happens absolutely at random, any speed, hot or cold. In my recent 300+ miles trip it stayed off for about 150 miles straight. Appreciate the assistance!!

 

[TJBaker57]

Seeing as the abs/ brake light popped up today the second I plugged in my phone charger,

If this happened today before you read these codes then we need to rerun the exercise as I mentioned a few moments ago. In particular the old and pending codes would be worthy of a look. "Old" codes are those that have requested the MIL in the past but are not currently requesting it. A pending code would normally be one that requires an issue to be present on 2 consecutive drive cycles.

 

[mrrsm]

Did you Isolate, Remove, Clean, Apply Dielectric Grease and Re-Attach the Related Grounds in the ABS Circuit?

Electrical Ground locations

While troubleshooting a bad ground I came across some scans of the service manual regarding electrical ground locations for our platform posted on another site. This includes both short and long wheel base, as well as both 4.2L and 5.3L. Credit goes to Wex...

gmtnation.com

 

[Dadwagon]

So far through this process, I've cleaned and reinstalled left and right engine bay grounds, ground under driver feet plus sprayed plastidip on that particular ground site, cleaned the 3 fuse box grounds, replaced the the OEM negative battery screw that stripped, removed and popped back in every fuse. Battery is correct size and about a year old, Junkyard-branded. Throttle body removed and cleaned. Front ABS sensors cleaned and reinstalled, no rust anywhere on them.

I have not cleaned the four grounds on the side of engine itself, that's next on the list.

Seeing as I've had the ignition switch temporarily fail twice in the past, probably worth replacing the ignition switch to see if that is the weak link in the EBCM screaming failure.

 

[TJBaker57]

ground under driver feet

This would be G304 on the left frame rail beneath the truck, right?

 

[Dadwagon]

G305 left frame rail. That actually didn't look too bad when it was removed. This vehicle is rust-free from Texas and Arizona, but that also mean it's been subject to extreme heat.

 

[TJBaker57]

Have you tried running the codes again, this time requesting old and pending codes?

 

[Dadwagon]

Will also look for G403 per the ground wire guide MRRSM posted.

 

[TJBaker57]

Curious... The wiring diagrams identify the EBCM ground as G304. Looks very much like G305 in MRRSMs link.

 

[Dadwagon]

I woke up today to find the rear wiper has stopped working, but the wiper fluid button and squirter work fine. There must be a rear ground I need to clean.

EDIT: Nope it was the lift gate wiring that must have gotten smooshed, I removed the rubber covers and white plastic guides, all the wires look fine, put them back in, put the rubber and plastic pieces back into place, close lift gate. Wiper working again.

How can wires on a big GM truck be so prone to grounds and failures? I appreciate the fix was sort of easy but it took some searching and thinking to make the fix.

 

[Dadwagon]

Update: Rear wiper failed because the orange wire that feeds it in the rubber liftgate hinge broke. Also the black ground wire had the housing cut. Stripped wire, tied wire, shrink wrapped. Wiper back to normal. I will not doubt the advice of the GMTNation again. You are keeping my poor a$$ on the road and I really appreciate all y'alls help.

 

[mrrsm]

Even if you are still unable to read and access any "C" Codes, try following THIS Dude's ABS Sensor Diagnosis for measuring the ABS Sensor Alternating Current milli-voltages via a DMM - DVOM while simply Spinning the Front Tires by Hand ...Before and After... performing the Rust Clean Up of the ABS Sensors seat locations on their upper Cast Iron Hubs:

Also... Is there any chance that you can Post the Link back here to the Thread you used that 'spilled the beans' for the solution about the "Lift Gate Boot Wiring Short-Outs"?

 

[Dadwagon]

Have cleaned the ground at the fuel tank rear of the back driver side wheelwell, and the ground at the frame rail just in front of the rear driver side wheel. They were barely rusty at all. No ABS/Brake light has come on in the last 50 miles, but that means nothing, it comes on at random.

 

[Mektek]

While the guy is cleaning around the wheel speed sensor hole he neglects to plug it. That hole gives direct access to the wheel bearings - where the dirt and rust being cleaned off will fall into unless it's plugged. When the bearings are ruined from the dirt falling in - that sucks!

 

[Dadwagon]

Update: Have replaced the ignition switch with a new OEM switch. Also put ceramic brake grease on all the pads and clips as they were squealing. Additionally, I got the truck on stands and tested the front wheels for bearing play by pushing/pulling vertically, seems like the wheel bearings are ok from my amateur analysis.

ABS/Brake lights continue to come on at random.

Will be removing the EBCM from under the car soon and re-soldering inside the box to see if that does the trick. It appears I don't need to add solder to each point but rather just re-energize the solder that's already in place. I'm on a shoestring budget of time and money, so I'm hoping I can get this issue fixed with a couple hours of sweat equity.

 

[prattage]

Here is a youtube demonstration I just made of the above mentioned code reading. Shows I have 2 history codes... C0267 and C0291

I don't want to hijack or revive an old thread. But I'm having an issue with reading codes with this exact setup I can not get the terminal to spit out anything. It just says "CAN ERROR" @TJBaker57 can you pm me as you seem to be very knowledgeable in this subject.

 

[TJBaker57]

I don't want to hijack or revive an old thread. But I'm having an issue with reading codes with this exact setup I can not get the terminal to spit out anything. It just says "CAN ERROR" @TJBaker57 can you pm me as you seem to be very knowledgeable in this subject.

First off, what year is your truck?

 

[TJBaker57]

PM sent. For anyone interested I believe the issue is that an ELM327 remembers the last protocol it connected with. This becomes the default. I think the OPs adapter is attempting to connect to the 2004 Tahoe with 5.3 using CANBUS. It needs to be told to use SAE J1850 VPW. This is done by sending the instructions to the adapter as "AT TP2". This means 'Try Protocol 2'.

 

[Dadwagon]

Update: Have performed surgery on the EBCM. The black gasket that seals the metal around the circuit board had at least four places where it had failed and disintegrated enough that moisture could have gotten in. I *poorly* added flux and resoldered all the big points on the board, some of them looked like they were missing a flake of solder on the tops, so those were probably what was failing. The board is covered in excess flux now around the solder points, and I may have used too much black RTV gasketmaker to reseal it, and I may have only waited an hour before reassembling and only about two hours before driving the vehicle ignoring the 24-hr cure time, but the truck runs without throwing any codes for the first 40 miles of testing. Usually it would go on after the first 5-10 miles, so I'm cautiously optimistic about the results. Additionally one of the valves and valve body was rusty, so I cleaned it up with rubbing alcohol and q-tips, and dried it all up before reassembling.

Removal and reassembly is not as gobsmacking as doing the intake manifold, but it was a pain in the rear without a lift and I was worried the ABS unit would fail and leave me stranded for work the next day. But it runs with no issues and the ABS work properly.

For those undertaking this project: Make sure you have a T20 Torx, there are a couple different sizes that look and feel exactly that size but they aren't the same and this is a blind removal/install so having the right size, and having it in a small bit that you can easily insert by hand, is key. I had a hard time reaching the four bolts and removed the entire ABS metal carrier from the frame to make it easier to access the bolts on frame side. The gasket on the plastic/resin board side can be removed from the channel with a tiny screwdriver - there is one screwdriver size that fits right in the channel.

Cost of sending in this unit for remanufacture is $150 plus shipping so this saved me at least that much. Let's hope this fixed the problem and doesn't resort to that.

Thank you all very much for your help, TJ Baker, MRRSM, Reprise.

 

[Mooseman]

I was worried the ABS unit would fail and leave me stranded for work the next day

The worst that could happen is the ABS won't work. You'll still have brakes, they'll just lock up if you hit them hard.

At least you were able to fix it yourself. Still makes me shake my head why they don't seal these better.

 

[Dadwagon]

I'm about 125 miles in with a couple steep hills up and down, no ABS/BRAKE lights, I'm calling this issue fixed. The ABS works great but it rarely comes on the way I drive. The Dadwagon carries precious cargo and does lots of coasting and light braking ahead of time.