ABS / TCS off throwing C1242 Code

[1999montana]

Our '99 Montana van just started throwing ABS codes yesterday. My neighbor is a mechanic and he used a small Sun scanner to read the ABS code(s).

Vehicle History:

Both front hubs were replaced at different intervals:
- LF in 2006 at about 134,000 Kms
- RF in 2010 at about 210,000 Kms.

No movement found or growling sound detected from the front hubs.

Rear hubs have never been replaced. Van has 295,000 Kms presently.

RF had a small issue with the Sensor connector about a year ago, but the connector was cleaned with electronic parts cleaner and packed with Dialectric grease.

No issues until now. Scanner reports a C1242 code (which is generated typically on right turns).

This code, if the scanner is interpreting it correctly indicates the ABS module.

The exact message is: "C1242 rear expansion spring can not hold motor"

The van has a Delphi DBC7 ABS antilock brake module according to documentation I have read.

On a long shot, I pulled the taillights out to see if water had entered either circuit board - both bone dry.

Do I conclude the ABS module is now defective?

Thoughts anyone?

[1999montana]

One more thing. The brake pipes were all replaced about a year ago when I broke the LF front pipe just below the ABS module.

Lost all of the brake fluid and had the van towed to our shop where they replaced all the steel lines and bleed the ABS module as well.

I had our shop do the work because it required a scan tool to work through the bleeding process of the ABS system.

Don't know if this is significant or not.

[Tech II]

There is an EBCM module and a Brake Modulator(attached to M/C)......

The bottom of the modulator comes off.......there are three gears....LF, RF, and Rear.....make sure the rear gear nut is tight and the gear is not loose.....if it is loose, tighten and using the scan tool, "re-home" the motors....

If ok, then you have to follow the trouble tree, to determine if the module or the modulator is the problem....

[1999montana]

Originally Posted by Tech II

There is an EBCM module and a Brake Modulator(attached to M/C)......

The bottom of the modulator comes off.......there are three gears....LF, RF, and Rear.....make sure the rear gear nut is tight and the gear is not loose.....if it is loose, tighten and using the scan tool, "re-home" the motors....

If ok, then you have to follow the trouble tree, to determine if the module or the modulator is the problem....

I'll take some pictures of the modulator and the control unit tomorrow and post here in this thread. I'm not quite sure which parts are serviceable based on your comments.

As I recall, the modulator appears to be attached directly to the master cylinder. Lines from the modulator go to the Delphi brake module on the fender well area not far from the firewall. The lines that broke were attached to this module, but hidden in behind and below the unit. It looked to me that the only way to get to the lines was to remove the master cylinder / modulator as a unit to gain access to the lines behind the Delphi unit.

Once I saw what I was up against, I decided to let the professionals work on it.

If I understand your comments, the code C1242 relates to internal parts in the modulator attached to the master cylinder.

[1999montana]

Originally Posted by Tech II

There is an EBCM module and a Brake Modulator(attached to M/C)......

The bottom of the modulator comes off.......there are three gears....LF, RF, and Rear.....make sure the rear gear nut is tight and the gear is not loose.....if it is loose, tighten and using the scan tool, "re-home" the motors....

If ok, then you have to follow the trouble tree, to determine if the module or the modulator is the problem....

Again, thanks for the reply.

The ABS modulator module is virtually inaccessible from the top, and I'm guessing not much better from below looking up.

I found the service procedure but I'm thinking two things:

1) The loose gear is the most common root cause as you mentioned and is highlighted at the beginning of the service diagnosis for this code.

Getting at the underside of the ABS seems to be a problem, unless the master cylinder and ABS module have to be separated to service the gears.

That would mean re-bleeding the system using the scan tool.

At a minimum the scan tool is needed to re-home the motors in the ABS after tinkering with it.

2) If the gear(s) are already torqued to spec, then it would likely lead to something else I would think.

There are virtually no service parts available for this vehicle's ABS / TCS modules now, so with 3 or 4 hours labor I could still have an issue and no resolution.

Not complaining, just trying to justify the expense.

I've included a shot of the ABS mounted to the side of the master cylinder, and the Traction Control Motor Module which really makes things cramped.

Overall, I'm leaning toward having the shop diagnose and attempt a repair rather than me.

Thoughts?

[Tech II]

Been awhile since I worked on one of these.......can't remember how much clearance is under the gear cover or how many screws, to check those gears..

[1999montana]

Thanks again.

Explained the potential problem to my neighbor (the licensed mechanic) and he wants to look at it himself (when he has time). He has the skill and the tools, so I figure it's better than me stumbling around. He tells me the best way to get at the ABS is to take it and the m/c out as a unit and take it to the bench.

Means bleeding everything again, but at least he can flush the m/c and check to see if any of the solenoids / motors might be sticking or binding in the ABS and correct the loose nut on the rear wheel gear.

I'm thinking that when the boys at the shop bled the system and ABS, they may have flushed out some bad stuff that had been trapped in the ABS module forever. I don't even know if flushing the old fluid would automatically flush the ABS / TC and it's internal components.

I remember asking on the Forum if I should open the bleeders on the ABS and TC module a long while back and the answer was no, leave well enough alone. Since the ABS and TC are at the highest point in the system after the m/c I was concerned that any air that might be in either one might get trapped there.

My GM dealer never did bleed the entire system to my knowledge, even after repeated complaints of spongy pedal. They bled the 'system' and adjusted the parking brake, but the brakes always felt spongy.

When my shop did the brake work last year, the brakes worked far better after the shop bled everything. And then along came this pesky chassis code.

Will report back to the board after my neighbor looks it over.

[sergeimoskva]

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[Tech II]

Good one, Sergei.....

[1999montana]

Well, it seems as abruptly as it started acting up, the ABS module settled down after a number of 'resets' to the rear motor.

I'm guessing that having the entire system drain of brake fluid last year, replacement of all the steel lines and re-bleeding of the system and ABS may have caused some sticking of the rear motor. A couple of times I heard the unit cycle as I put the van in gear and released the service brake. And then the other day, it seemed to act just fine and hasn't repeated the code in over a week and a half.

Wondering if bleeding the system through gravity might pull some possible contaminates out of the system? Or, is it better just left alone now?

[Tech II]

If all the motors are re-homed, I suck clear brake fluid through the lines with a hand vac pump......topping off fluid in the reservoir as it drops....

[1999montana]

Originally Posted by Tech II

If all the motors are re-homed, I suck clear brake fluid through the lines with a hand vac pump......topping off fluid in the reservoir as it drops....

Thanks for the reply.

Well, it looks like the ABS module has been able to 're-home' the rear motor after a week of unsuccessful attempts on its own.

I just wondered if I should try to flush the system after this happened.

We didn't touch it, but were going to when my neighbor had time. Now it looks like the ABS has corrected the fault on its own.

I figured since the master cylinder was the highest point, if I opened the bleeders on all four wheels (one at a time) in the order you bleed the brakes normally (into a container with some brake fluid in it), gravity would purge whatever might have caused the motor to stick or bind.

Fuzzy logic??