Annoying AH Problem
Drifting
Joined: May 2004
Posts: 1,822
Likes: 2
From: San Clemente CA
Hey Bill, thanks for the gut shots of the sensors. Interesting photo-essay there. So basically the sensors are miniature alternators that send a progressive voltage signal to the EBCM? DeeGee said the problem happened under light braking, so perhaps the signal generated is not large enough at that point. He mentioned that things were OK under heavier braking. Perhaps it is a rough connection and the signal isn't quite getting thru.
Thanks for the education!
Thanks for the education!
Last edited by TheDVS1; Nov 4, 2007 at 08:05 PM.
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
DeeGee
Take a CLOSE look at your wheel alignment. If your steering wheel is misaligned to the left or right while your wheels are actually STRAIGHT, the Steering Wheel Position Sensor (SWPS) will tell the EBTCM that you want to be turning (what ever way the steering wheel is pointing) and the accelerometers will be telling the EBTCM "Hea, were actually going straight!!" and it will cause the EBTCM to try to correct the direction of the car by applying the brakes on one or two wheels.
The C1278 DTC is TCS Temporaliry Inhibited by the PCM. If this DTC is present, you "SHOULD" also be seeing some other DTC which is actually causing the C1278 to set. How are you reading the DTCs????? Are you using the C5 DIC DTC or an aftermarket DTC Code reader?
Make sure that there are not any other DTC present. If they are ,,please list them.
If there are not any other DTCs, you could have a bad EBTCM. In that case,,,I would contact one of the EBTCM Forum rebuilders, give them your symptoms and see if they can rebuild it for you. There are some EBTCM problems that can NOT be repaired.
Please let me know if you have any more questions
BC
Take a CLOSE look at your wheel alignment. If your steering wheel is misaligned to the left or right while your wheels are actually STRAIGHT, the Steering Wheel Position Sensor (SWPS) will tell the EBTCM that you want to be turning (what ever way the steering wheel is pointing) and the accelerometers will be telling the EBTCM "Hea, were actually going straight!!" and it will cause the EBTCM to try to correct the direction of the car by applying the brakes on one or two wheels.
The C1278 DTC is TCS Temporaliry Inhibited by the PCM. If this DTC is present, you "SHOULD" also be seeing some other DTC which is actually causing the C1278 to set. How are you reading the DTCs????? Are you using the C5 DIC DTC or an aftermarket DTC Code reader?
Make sure that there are not any other DTC present. If they are ,,please list them.
If there are not any other DTCs, you could have a bad EBTCM. In that case,,,I would contact one of the EBTCM Forum rebuilders, give them your symptoms and see if they can rebuild it for you. There are some EBTCM problems that can NOT be repaired.
Please let me know if you have any more questions
BC
Bill
Thanks as always for the great advice.
The wheel is fractionally off but we really are talking a hairs breadth. Just a tad to the left. How tight are those tolerances? What I cant figure is if the sensor is sending a signal that the wheel is off why the difference in light or heavy braking?
Its actually a C1287H that sets which is the SWPS. No other codes at all. I'm using the DIC to read them. I already had a brand new EBCM at about 28k miles and I only have 36k now. At that time I was throwing a C1214 and the replacement fixed that. I'm tending more towards sensors at present.
I've just had it up on the ramps and taken a look at those connectors. They were dirty but looked sound. I gave them a good clean with electrical cleaner so we'll see if that makes any difference. The ones on top of the chassis frame are PITA to get at.
I may have to bite the bullet and change out that SWP sensor if this doesn't fix it. Not looking forward to that.
Last edited by DeeGee; Nov 4, 2007 at 04:04 AM.
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Maybe its fixed
Well I just took two runs out today having cleaned up the hub connectors and maybe I'm onto something.
Two 25 mile runs and than two five mile trips and not a single trip. A good selection of country lanes and some long straight stretches as well.
The AH is not chattering as much even under gentle braking. I just had one very slight jitter but it didn't cause a trip. Its definitely way better than it was so it looks like the conenctors are the problem.
If a shot of electrical cleaner has done the job I'll be well happy. Thanks Bill for posting the thread on the connectors. You may even have forgotten that one as it was many moons ago. Thanks also to BlackZ06 for the help
Two 25 mile runs and than two five mile trips and not a single trip. A good selection of country lanes and some long straight stretches as well.
The AH is not chattering as much even under gentle braking. I just had one very slight jitter but it didn't cause a trip. Its definitely way better than it was so it looks like the conenctors are the problem.
If a shot of electrical cleaner has done the job I'll be well happy. Thanks Bill for posting the thread on the connectors. You may even have forgotten that one as it was many moons ago. Thanks also to BlackZ06 for the help
Last edited by DeeGee; Nov 4, 2007 at 07:57 AM.
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Deep Gloom
Well another potential fix out the window
It seems better but I'm still getting trips.
I've tried a bit more fault finding. On a long straight stretch of road I tried the cruise control. It tripped out and took 3 attempts to engage.
The AH trips seem to be more common in one particular section of the drive to work. Again a long straight road with a switchback. The hills and valleys are quite steep and I've had a couple of trips there. I tried disengaging AH for that stretch and it tripped out even though it wasnt selected. AH trips out TCS stays engaged. Does that tell me anything? Wiring or connectors rather than sensors maybe?
Its a real pain because its been wet here this week and AH is quite nice to have in these conditions on twisty back roads.
It seems better but I'm still getting trips.I've tried a bit more fault finding. On a long straight stretch of road I tried the cruise control. It tripped out and took 3 attempts to engage.
The AH trips seem to be more common in one particular section of the drive to work. Again a long straight road with a switchback. The hills and valleys are quite steep and I've had a couple of trips there. I tried disengaging AH for that stretch and it tripped out even though it wasnt selected. AH trips out TCS stays engaged. Does that tell me anything? Wiring or connectors rather than sensors maybe?
Its a real pain because its been wet here this week and AH is quite nice to have in these conditions on twisty back roads.
Racer
Joined: Sep 2006
Posts: 260
Likes: 1
From: Chesterfield MI
Just a side note to those who responded.....The steering wheel position sensor is actually in the steering rack and the AH system will actually "learn" the center position after a reset of the codes, so alignment cannot be the issue. I'm sure your far past that, but I thought I'd chime in. The plug for the connection is attached to the power steering cooling line in front of the ABS module.
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Just a side note to those who responded.....The steering wheel position sensor is actually in the steering rack and the AH system will actually "learn" the center position after a reset of the codes, so alignment cannot be the issue. I'm sure your far past that, but I thought I'd chime in. The plug for the connection is attached to the power steering cooling line in front of the ABS module.
Thanks.
Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Just a side note to those who responded.....The steering wheel position sensor is actually in the steering rack and the AH system will actually "learn" the center position after a reset of the codes, so alignment cannot be the issue. I'm sure your far past that, but I thought I'd chime in. The plug for the connection is attached to the power steering cooling line in front of the ABS module.
ISEERED
The Steering Wheel Position Sensor (SWPS) (which is also called " High Resolution Steering Wheel Position Sensor" Part# 38 in the 02 service manual Legend and 27 in the 98 service manual and is located on the lower end of the steering column near the fire wall. The ONLY electrical connection on the steering rack is the connection for the MAGNASTEER component. MAGNASTEER controls the feel of the steering wheel during various vehicle speeds.
The SWPS is a VERY precise resistor sensor and if it doesn't produce the correct outputs, the electrical signals to the EBTCM will be corrupt and do very strange things. There are TWO other sensors that contribute to the EBTCM's operation. The Lateral and Yaw Rate Accelerometer.
DeeGee
Do you have access to or can you have someone read the STEERING WHEEL POSITION SENSOR (SWPS) and the Accelerometers with a GM Tech II.
If it were me, I would insert two wires into the phase A and Phase B outputs of the SWPS and examine their outputs through a couple 90 degree steering wheel rotations.
BC
Last edited by Bill Curlee; Nov 18, 2007 at 06:22 PM.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
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From: Van Buren Arkansas
Wounded Warrior Escort '11
Bill is the expert but will throw my 2 cents worth in. Mine went bad quite a few years ago. It would trip whenever going over speed-bumps and other similar places. Finally had the dealer replace it and no problems since.
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Thread Starter
Tech Contributor
Joined: Dec 2003
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Bill, I'm afraid I don't have access to a Tech II. maybe I should stop being a cheapskate and shell out some $$
I guess its obvious by now that I'm not looking forward to replacing the sensor
Last edited by DeeGee; Nov 19, 2007 at 03:57 PM.
Intermediate
Joined: Jun 2003
Posts: 40
Likes: 0
From: Tulsa Ok
I am getting the same C1287H code on my 04 coupe with 29,000 miles on the original Goodyears, could it be related to tire wear? I am planning on installing new tires in the next few weeks and also doing a 4-wheel alignment.
Intermediate
Joined: Jun 2003
Posts: 40
Likes: 0
From: Tulsa Ok
Annoying AH Problem
DEE GEE & Black Z06 or ANYONE WHO HAS INFO!
I have a 2004 coupe experiencing the same problems with the DIC setting the C1287 H Code. It happens when I'm on the turnpike and usually going straight at highway speeds and the roads are rather smooth. I have around 29,000 miles on the original Good Years. I am looking at putting on new tires in the next several weeks along with a 4-wheel alignment. The tires are noisy and the fronts are cupped some but pretty much standard for what I have seen for the C5. Could this be causing the problem? I am thinking about doing this before I take to my mechanic for any repair.
I have a 2004 coupe experiencing the same problems with the DIC setting the C1287 H Code. It happens when I'm on the turnpike and usually going straight at highway speeds and the roads are rather smooth. I have around 29,000 miles on the original Good Years. I am looking at putting on new tires in the next several weeks along with a 4-wheel alignment. The tires are noisy and the fronts are cupped some but pretty much standard for what I have seen for the C5. Could this be causing the problem? I am thinking about doing this before I take to my mechanic for any repair.
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 29
From: San Rafael CA
If the codes continue to appear after the service work ... post again with the specific codes and people here on the forum can help you in diagnosing/fixing the problem
Le Mans Master
Joined: May 2006
Posts: 7,802
Likes: 205
From: Hillsboro OR
Calling DeeGee...
Did you ever get to the bottom of your C1287H code. My 03 Coupe is experiencing the exact same problem under the exact same conditions. Did you ever replace the SWPS? I would love to hear how you resolved it. 
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
I'm coming up for a brake pad change. I'm going to do that before I do anything. I also thought I'd spray some electronics cleaner on the SWPS to see if it may be a dirty contact. A long shot but it costs nothing.
If all else fails I'll probably have a go at replacing the sensor.
Last edited by DeeGee; May 9, 2008 at 12:01 AM.
Intermediate
Joined: Jun 2003
Posts: 40
Likes: 0
From: Tulsa Ok
I had the famous 1287H code and only 29,000 miles on an 04, took it to a Corvette Mechanic and he trouble shooted and replaced the steering wheel sensor. $75. part and 4 to 5 hours labor. Running great in Tulsa, OK! After the repair installed a new set of Michelin's and WOW what a difference!
