Has anyone either solved this issue yourself or had it taken care of at a dealership? Apparently, it signifies that there is a bad ground, but can also indicate the ABS pump is faulty, at least from what my searching has uncovered.

I've cleaned the three grounds (including the one near the battery)that most often cause problems, but none of them looked bad, as i seldom drive in the rain.

So, if you've had this code and fixed it, I'm all ears.

 

DTC C1242
Circuit Description

The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage.

The electronic brake control module (EBCM) controls each solenoid valve by grounding the solenoid.

The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes:

* Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events.
* Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.

Conditions for Running the DTC

* C1242 The system voltage is greater than 8.0 volts.
* The system relay is ON.
* The pump motor is commanded OFF.


Conditions for Setting the DTC
C1242



The pump motor is stalled or turning slowly.
Action Taken When the DTC Sets

If equipped, the following actions occur:

* The EBCM disables the ABS/TCS/VSES for the duration of the ignition cycle.
* The DRP does not function optimally.
* The ABS indicator turns ON.
* The Traction Control and Active Handling indicator turns ON.
* The DIC displays the following messages:
o Service ABS
o Service Traction System
o Service Active Handling

Conditions for Clearing the DTC

* The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
* The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids

The pump motor is integral to the BPMV. The pump motor is not serviceable.

Test Description

............................Inspect for poor connections at the pump motor harness pigtail connector of the BPMV.

Inspect for poor connections at the harness connector of the EBCM.

locate the BPMV ground lug connection, making sure you have continuity to ground.. ... the BPMV, is the module bolted/connected to that ECBM

 

My 2000 manual states that resistance greater than 6900 ohms in ground circuit 1250 will be the likely culprit to set the code.
The portion of the circuit you can easily reach consists of the ground terminal in the side of the pump motor, that grounds to body terminal G101 via a wire.
The complete circuit, however, originates in the BPMV, and enters the motor thru terminal 8 of the Brake Pressure Modulator Valve, and runs thru the motor windings.
The high resistance could be occuring back in the BPMV, but hopefully is in the external ground wire, or in the connection of the BPMV to the motor.

So, I'll paraphrase the manual's diagnosis; starting with the easy stuff of course.
1. Clean the connections at the motor stud, check the wire to the body ground G101, and clean G101. You did this.
2. Check the resistance from the motor stud to the frame of the car.
Should be 2 ohms or less, virtually Zero. If it's more, you need to reclean those connections, and thank you good fortune.
3. After that it gets a bit tougher, you will need to dissamble the EBCM from the BPMV. Look for obvious problems like bad terminals, corrosion, or brake fluid in the terminal areas. If it's not repairable, may need to replace the EBCM or the BPMV. If there's brake fluid, you are toast, very probably need to replace both modules.
4. If all looks good, find terminal 8 going from the BPMV to the motor.
Ohm this out from terminal 8 to the external motor ground you checked previously. If the resistance is more than 10 ohm, it may be damaged motor windings or a bad internal motor connection. The book says to replace the BPVM at this point.

I've never had this code, so no personal experience with it. So, maybe some of the gurus can help a bit more.
I have had the 1243 code for slow-running motor, and I went in, found pin 8, and applied 12V to excercise the motor. Getting the modules apart is not too difficult, just wiggle in there and unbolt them. If you search under C1243 there are good photos/wrietups on getting the modules apart and finding pin 8.

DG

 

Dave

What year C5 do you have?

Like the WRENCH stated, you can apply 12 VDC to the motor circuit and get the pump motor to spin for a while and free up. Once it runs for a couple of 30 sec periods, it usually frees up and the DTC no longer pops. The dealer will want an arm and possibly both legs to replace the BPMV. They might even tell you that they are replacing the EBTCM. Ive seen the bill for those repairs before and you better be sitting down and have taken some Valium before you see the bill!!!! Its like $1500.

If you have a 2001+ c5 the BPMV motor plug connects under the MAIN EBTCM connector and is very easy to get to and apply 12 VDC to.

Answer me this question. Do you ever activate your ANTILOCK Brakes or get ACTIVE Handling to kick in?

Bill

 

Thanks for the tips, everyone.

Bill, It's a 2001. The repaired EBCM is about 1 year old and I'd say antilock kicks in far more often than active handling. I haven't looked around in the EBCM area in a while. Is that where the BPMV motor plug is? My guess is that it is unlikely that a connector or ground is corroded, based upon what the ground stud components and connecter pins I disassembled and the fact that my car rarely sees rain.

Edit: After rereading all the posts, I believe 12V is applied to the BPMV after the ebcm is disconnected. Is that true or is there a wire connection that is separate?

Dave

 

Dave

When I get home I will send you some pictures of that plug. It plugs on the EBTCM. There are TWO connectors on it. One is BIG as it is the main EBTCM connector and theres a small two wire connector directly under that main connector. Thats the plug that runs the BPMV motor.

Unplug the main EBTCM cannon plug and getting to the small motor plug is a snap.

The ONLY time that theres power on that plug is when the EBTCM tells the BPMV Motor to run.

Bill

 

Great - thanks, Bill, Trussme, and the Wrench.

Dave

 

Pictures of the EBTCM with the BPMV Motor electrical connection:







Bill

 

Thanks, Bill,

I'll be taking this on, this weekend, sometime after having new GSD3s installed. I would guess that pin 8 is easy to find? As DG suggested, I'll find the 1243 post, just to be pre-prepared.

Dave

 

A funny thing happened on the way to Discount Tires, this morning.........

Actually, it happened a little bit later: When I handed the counter guy my keys, I mentioned to him that when the car is started, the ABS, traction, control, and active handling warnings will display in the digital information console, along with the respective warning light symbols.
15 minutes later, after the two front GSD3 tires were installed, the tech backs my car out and comes inside to get me. Quickly, I grab the keys and start up the engine. What the? NO WARNINGS AT ALL! I drove home and later reclamped the main harness to the EBCM and tightened the nuts holding the BPMV to the engine. I then turned the ignition switch to ON and once again - no warnings in the DIC and no litup symbols on the dash.

Now how can changing the front tires solve the problem? The warning displays have been rearing their ugly heads for two weeks, at every startup.

I admit, I'm puzzled!

 

Gotta Love these C5s!....they are a mystery sometimes. All it took was someone else to sit in your seat!

 

I could be way off base here but, putting the car up/or taking a car off of a lift-ramps-etc.. could cause enough of a jostle to either make or break a loose/dirty/corroroded electrical connection. Its odd, but it does happen. I would still look over the connctions etc.. I know it sounds like I'm making this up but I'm an electrcian and trouble shoot a lot of wierd problems. One of the most common is a loose connection where two conductors are touching each other making a closed circuit. Vibrations such as walking on a floor, slamming a door, even the connections to the bldg service itself can be affected by wind, can cause the conductor to move enough to open the circuit. Sorry for the long post, just throwing out another idea.

 

George

Your theory is very sound. They were working near each wheel. Using air tools and lift equipment connected to the FRAME. Its very possible that the troubled circuit got jostled and your good till the FRET Corrosion that was disturbed grows back. Time will tell.

BC

 

That does sound possible, guys. Now when I look at the wire harness that starts at the EBCM, heads downward and splits off at some point, it sure looks like some the ground wires end up at the connection at the right (passenger side) front chassis ground connection. I thoroughly cleaned that, its connector, the opposite side and its connector, and the ground stud near the battery, a few days ago, so it is doubtful that any were causing the C1242 code. Perhaps there is another ground point that I am missing. I'll double-check to see where the other ground points are located.

The good news is that it is likely that a ground connection is the culprit.

 

Ahhh, electrical gremlins.
They say the universe always strives for equalibrium; so maybe all my bad experiences at Discout Tire are just being offset - you lucky devil!

Similar story: I searched all over my nephew's '04 for an intermittant radio, replaced some very expensive parts and took the whole car apart several times. Probably spent 50 hours on it.
Then his wife gets in the passenger side with spike heels on, puts her foot down on the corner of the carpet, and the radio comes on!
Mashed data buss wire.

Glad it's working.

DG

 

Well, i had a feeling it wouldn't last and sure enough, that dang thing reared its ugly head again. Just to be clear about accessing pin 8, its it visible after removing the latched connector on top of the EBCM? Based upon what I've sen when doing a search, the motor needs to be exercised if the C1243 code shows up, but I have the C1242 code which should mean there's a bad ground somewhere (or the BPMV is internally shot).

 

Dave

Check out this schematic:



Use a meter and PROBE the EBTCM side of the connector and find out what pin has battery voltage to ground when the key is in the ON position. That pin is the 12 VDC POSITIVE pin on the pump motor side. The other pin is NEG 12 VDC. Connect a 12 VDC power supply to that connector and the pump motor should run. The two pin connector is in the pictures that I provided above.

Bill

 

Ah, that's the connector just below the bayonette-latched connector. It'd been a while since I removed and reinstalled my EBCM. Thanks, Bill. I guess I have nothing to lose. In fact, I just bought a convenient "10 FT Retractable Test Leads" reel at Sears. ($10) It's good for 10 amps. Here's a picture at a more expensive site.

http://www.powersportequipment.com/p...star&category=

Side note: for those who find the above diagram a bit small, try holding down your keyboard's CTRL button while scrolling the mouse wheel. That should zoom you in, nicely.

Dave

 

Well, I think I fixed the problem by unplugging and plugging each of the two connectors a few times. It's been 8 months now and I've not seen any " Service ABS, Active handling, or traction control" messages or warning lights.

I had already cleaned all of the relavent ground connections but only after plugging and unplugging the connectors did I get rid of the warnings.

 

Well, can you pass some of that luck my way.
I started getting the 1243 code again a couple weeks ago, after going in and exercising the motor about 6 months ago.
For my 2000, you have to split the ABS modules apart, which is a pretty tough job. This time I ran the motor for several 1 minute passes, which barely warmed it up. So maybe it will behave longer this time.
Next time I plan to tap into the power wire, which runs right along the top of the motor on the 2000, and put a connector on there to apply 12V easily.

- I read herein that GM doesn't even offer replacements for the pre '01 cars anymore - at any price.

- I also have the theory that many of the module failures are due to relay for the motor burning up due to the high resistance in the motor.

DG