ABS / TCS on again after dry spell

[1999montana]

I think I'm beginning to lean toward an electrical connection problem, external to the van's wiring. Probably the connector that comes from the middle of the van's floor connecting the fuel pump, and possibly the rear ABS sensors.

Reason:

The van was dry for about 2 weeks, and the problem seemed to heal itself. Yesterday we had two or three down pours, and although the van didn't go anywhere, this may have set the stage for a bad connector contact to cause some havoc.

As I drove the van today, the symptoms kept changing. First the ABS / TCS lights came on, and with each re-start they went out. I pulled the fuse to the ABS / TCS IGN and started the van without it. The warning lights came on immediately. Replaced the fuse, and the ABS went out, but the TCS stayed on.

Restarted the van and both the ABS / TCS and Brake warning light came on. Re-started again and everything went out, until I turned a corner.

Either the water is in the floor pan near the connector, or there is water on the connector under the van that is causing the problem. Everything else, including the ABS module and TC module appears to be working fine.

Going to crawl under the van when it stops raining and check things out, clean things up and plaster some dielectric grease liberally.

NOTE: We had an incident with the power door locks about 15 years ago after a long trip out west. Plocks wouldn't work on the passenger side. Took the van into the dealer and they fixed the problem, but reported that there was water coming in the cabin 'somewhere' that would have to be fixed.

On careful thought, I may have determined the 'root cause'. When the van was about 2 years old, we got caught in a car wash that stopped dead, with the overhead brushes beating on the top of the van immediately above the windshield (this went on for about 3 minutes until I could get them to shut everything down).

Over time (maybe 5 or 6 years), the black masking at the top of the windshield on the inside began to etch and peel. Makes me wonder if during heavy rain, the water is finding it's way in between the windshield and the roof line in the pinch weld area.

Probably the only way to find out is to have the windshield removed.

[Tech II]

Would help to know what the ABS code is to have a starting point.....

[Stealthee]

I'm betting you have a chafed/broken wire going to one of the hubs. Have it scanned with a scanner that can pull abs codes so you know which sensor is tripping the light. Once you have that information you can start tracing wires.

[1999montana]

Originally Posted by Tech II

Would help to know what the ABS code is to have a starting point.....

UPDATE: ABS / TCS is out again.
Dry as a bone around these parts for 48 hours now.
Think this tends to confirm an electrical problem somewhere.
Will crawl underneath and investigate after our company leaves today.

Thanks again for the reply.

Well, it started with C1242 which mysteriously corrected itself as we entered a dry spell with warmer weather.

If it was a motor / gear nut problem, it wouldn't go away on it's own, I would thing. If it were the motor was sticking or binding, maybe. Seems to have been triggered by moisture.

The fact that it generated some other codes (didn't scan for them, but they appear to be 'stray') as described by the symptoms / warning lights suggests it's not a mechanical problem, but an electrical one, brought on by rain and moisture.

I'm going to pull all the connectors on the underside of the van that I can get to, (the rear hubs are a PETA as the wires are tucked behind the hub), check for corrosion and clean and grease them to see if the system settles down.

Worst case, I get my neighbor / mechanic to pull the ABS module off and check the general operation and the gear nuts.

[Tech II]

I would swap out the electronic brake control relay, just in case there is an intermittent contact problem, and also check the ground to the brake control module.....

[1999montana]

Originally Posted by Tech II

I would swap out the electronic brake control relay, just in case there is an intermittent contact problem, and also check the ground to the brake control module.....

Thanks for the reply.

Will come back to the board after doing a complete check of the electricals and replacing the relay.

[1999montana]

Originally Posted by Tech II

I would swap out the electronic brake control relay, just in case there is an intermittent contact problem, and also check the ground to the brake control module.....

Feeling a little helpless. Looked in the fuse panel under the hood and on the dash panel right side, but I don't see a relay marked as a brake control relay. Not even sure I know what it looks like, although I have seen different conflicting pictures of what might be the right relay, but then I have no idea where it would plug in.

Where should the ground reference for the Brake Control Module be?

Help ...

[Tech II]

Looking at the wiring diagram, it does not give the location of the relay...it shows it being external to the EBCM/EBTCM......chances are it's hanging somewhere in the engine compartment by itself or with other relays...

I see 3 connectors going to the EBCM/EBTCM module......C2, has terminal C(red) that is the power from the relay, so you can back probe that connector to see if you are getting power from the relay(key on).....C2 terminal D(blk) is your ground circuit......so if you back probe terminals C and D of C2, and turn the key on, the test light should light verifying power from relay, and a good ground....remember, all 3 connectors have to be attached to the module for this test....

[1999montana]

Originally Posted by Tech II

Looking at the wiring diagram, it does not give the location of the relay...it shows it being external to the EBCM/EBTCM......chances are it's hanging somewhere in the engine compartment by itself or with other relays...

I see 3 connectors going to the EBCM/EBTCM module......C2, has terminal C(red) that is the power from the relay, so you can back probe that connector to see if you are getting power from the relay(key on).....C2 terminal D(blk) is your ground circuit......so if you back probe terminals C and D of C2, and turn the key on, the test light should light verifying power from relay, and a good ground....remember, all 3 connectors have to be attached to the module for this test....

You've heard the stories about the apprentice that was sent into town to get a pail of steam, right? That was me today, LOL

On our '99 Pontiac Montana van, I pulled the left side of the engine compartment apart in search of the electronic brake relay. Removed the speed control, the brace that runs from the shock tower to the front rad cradle, and the recovery tank as well to create more access.

Looked high and low. Nothing. I did find one red wire (actually a heavy duty one I would guess to be 10 or 12 gauge), but it didn't terminate at the ABS or Traction Control unit.

There are four heavy gauge (10 to 12 gauge) wires plugging into the TC unit, but none of them are red (memory tells me they are blue, yellow, white and black).

Now that the drier weather has returned, the ABS / TCS is sometimes on, and sometimes off. It seems to cycle off for no clear reason while driving, not even touching the brakes.

The sound the ABS makes when it goes 'off' is like someone pulled the 10 Amp IGN ABS TCS fuse while the vehicle was in motion, and then the fuse gets replaced BUT, because the vehicle is in motion when this interruption occurs, the ABS / TCS gets confused and turns off.

If the key is simply left in the 'run' position with the engine off, the ABS / TCS light comes on when the fuse is pulled, and then goes out when the fuse is replaced. The only time the ABS tries to reset itself after this 'power fail' is when the engine is running.

I understand that the circuit connected to the 10 Amp IGN ABS is designed to energize the ABS / TCS 'relay' when the ignition is on, and the relay handles the higher current load the ABS demands when activated.

I'm beginning to think that there must be a module inside the passenger compartment on the driver's side that may also have the 'relay' OR, the relay is integral with the brake control module next to the ABS unit.

If this last point is true, then we can say goodbye to ABS, because this Delphi TCS module is no longer available.

[Tech II]

I agree.....I have tried to find it to no avail.......I know some relays are integral to the ABS module, and if the relay is bad, the whole module has to be replaced....

The only wiring diagram I could find shows it separate from the module, unless the diagram is wrong....it also shows a soldered wire coming off the line going to terminal C, which makes it look like it is external to the module....;

[1999montana]

Originally Posted by Tech II

I agree.....I have tried to find it to no avail.......I know some relays are integral to the ABS module, and if the relay is bad, the whole module has to be replaced....

The only wiring diagram I could find shows it separate from the module, unless the diagram is wrong....it also shows a soldered wire coming off the line going to terminal C, which makes it look like it is external to the module....;

It's OK, I know that there was a difference in production from '97 thru '99 and after that the standard shop and wiring diagrams were correct right up through '05. For some unknown reason the '99 is a 'one off' with some non-standard design characteristics.

Point to be taken here is that the van doesn't owe us anything and has more than paid it's way. Just don't like having something to fix that can't be.

I may pull the panels down under the dash (driver's side) and see if I can find a relay that clicks when the fuse is pulled / replaced. The trick would be to find one to replace it with. If I can't fix it, I may pull the instrument cluster and remove the bulbs - LOL

[1999montana]

Originally Posted by Tech II

I agree.....I have tried to find it to no avail.......I know some relays are integral to the ABS module, and if the relay is bad, the whole module has to be replaced....

The only wiring diagram I could find shows it separate from the module, unless the diagram is wrong....it also shows a soldered wire coming off the line going to terminal C, which makes it look like it is external to the module....;

Looky what my parts manager sent me ...

Right there in the kick panel area on the driver's side ...

Best part, all the electronics are still serviced, although the wiring harnesses are not.

[1999montana]

Well, I finally had a chance to get under the dash of the van to see where the brake control relay and EBCM were located based on the parts diagram.

Had hoped it was easily accessible through the kick panel area, but in truth, the EBCM and the relay are stuffed up in the dash next to the firewall and the parking brake lever

Wanted to eyeball the relay before buying a replacement.

As it stands right now, the underside of the dash, the finish trim and the plastic trim on the bottom of the dash where the OBDII connector is, have to come out/off to get closer the the relay. The EBCM is actually easier to get to than the relay.

Sure enough as Tech II mentioned, there is a heavy gauge red wire going to the relay that likely disappears through the firewall to the ABS module.

Still convinced I have some sort of electrical issue as the floor on the driver's side under the sound deadener and floor carpeting was wet with an 1/8" of water. Exactly where the water is coming in remains a mystery at this stage.

[1999montana]

OK, ABS fixed.

Windshield replacement (which eliminated water on the cabin floor) did not correct the problem with the ABS, but did stop water from coming in nonetheless.

Wasn't an ABS CM problem either.

Finally took it into our trusted shop and they did diagnostics on the ABS / TCS system and found that only the left front hub bearing was bad and intermittently causing the sensor to throw not a C1242 code, but a C1232 code. Third time the left front hub has been replaced since the van was new. Last hub had 130,000 Kms on it.

Didn't charge me for the diagnostic time, just the flat rate to re and re the left front hub with a new one.

No background on why the code originally appeared as a stray C1242 periodically.

Now I have to pull the interior panels from the right rear and figure out why my power sliding door stopped working. It could actually have been caused by water. Logic controller thinks the door is on the primary latch and buzzes when the van is in gear and sliding door lockout is turned off.

Oh joy!

[sergeimoskva]

Hi! GM has had a huge wheel bearing problem for a long time. Due to the poor design the ABS wheel speed sensors develop very wimpy signals to start with, then the wheel bearings develop a little play, which is normal, but in this case that's enough to let the speed signal drop out and set a fault code. In the case of wheel speed sensors the computer compares them to each other while you're driving. When a code is set for one of them, the computer knows it can't rely on that as an accurate reference for the others, so it won't run tests on them, and it won't set a fault code if a second problem occurs. Therefore , possible - and this was due to the wandering code . It's my opinion