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I was receiving the dreaded "SERVICE VEHICLE SOON" message almost every drive
My C5 is an early 1998 WITHOUT active handling.
After some troubleshooting, I have determined that the steering position sensor (GM part number 26055808) has failed.
For the 97's and 98's without AH (maybe 1999 and 2000 too), GM stopped making that sensor by 2010.. Those are long gone. A few 3rd parties made them for a few more years... those are now gone. No one has produced them in over 10 years. No one has any in stock. The only available source for these is junkyard cars.. And because of the shortage, people are asking upwards of $500 for them, untested and no warranty.
I believe later C5s (2001+) with active handling changed to a different steering sensor.. one that is still available.
Other than the nuisance of clearing the "SERVICE VEHICLE SOON" message, I'm not sure if this is actually a "problem".
As I said, the car does not have active handling.. and the traction control still seems to work correctly (and needs no steering angle input)
I read some VERY detailed threads and it seem the ABS in these early C5s does not use the steering angle input either.
So why is the sensor even there? Does ANYTHING use it's output?
I was receiving the dreaded "SERVICE VEHICLE SOON" message almost every drive
My C5 is an early 1998 WITHOUT active handling.
After some troubleshooting, I have determined that the steering position sensor (GM part number 26055808) has failed.
For the 97's and 98's without AH (maybe 1999 and 2000 too), GM stopped making that sensor by 2010.. Those are long gone. A few 3rd parties made them for a few more years... those are now gone. No one has produced them in over 10 years. No one has any in stock. The only available source for these is junkyard cars.. And because of the shortage, people are asking upwards of $500 for them, untested and no warranty.
I believe later C5s (2001+) with active handling changed to a different steering sensor.. one that is still available.
Other than the nuisance of clearing the "SERVICE VEHICLE SOON" message, I'm not sure if this is actually a "problem".
As I said, the car does not have active handling.. and the traction control still seems to work correctly (and needs no steering angle input)
I read some VERY detailed threads and it seem the ABS in these early C5s does not use the steering angle input either.
So why is the sensor even there? Does ANYTHING use it's output?
Has anyone figured out a solution to this issue?
Thanks,
Fred
In addition to Active Handling (which your car doesn't have) I expect that the steering angle sensor input is probably used by the (automatic) transmission to keep it from shifting while in mid-turn and upsetting the chassis. At least other cars function this way. You'll need to verify this functionality on the Corvette.
FWIW, whenever I needed an odd or discontinued part on my C4 years ago I would find that many other GM models shared the same part but with a different number. An example was headlight bulb connectors. Turned out most other chevy cars and at times trucks used the exact same part.
From what I have seen in looking for the part, this sensor was only used in 98 and 99.
oelarse - thanks for posting that diagram. My plan was to use a clone Tech2 to read the values, but when I installed the required software stack, I received harsh warnings about it containing a "known trojan". The maker of the device said to "just ignore this warning", but I am a Software engineer and I know how these things work.. No way I was installing those applications!
The sensor is pretty complex. It has both digital and analog output. The C1281 I'm getting is caused by a mis-match between those 2 outputs.
So to answer your question, it's just been a process of elimination. I did inspect and clean all the grounds involved in this circuit.
Another hint for me: I'm throwing the C1281 code, but I am NOT receiving the C1288
This great post from Mr, Bill from over 11 years ago contains a lot of good info. My car is a 6-speed manual... It looks like the "Magnasteer" will be disabled when in this condition. I believe that somehow (?) reduces the steering input at high speed?
Originally Posted by Mr.Bill
Here is the Theory of Op for the SWPS/EBTCM and what conditions set the code:
DTC C1281 Steering Sensor Uncorrelated Malfunction Without RPO JL4
Circuit Description
The EBTCM uses four inputs from the Steering Wheel Position sensor:
Phase A digital input
Phase B digital input
Index pulse
Analog input
This information is used to calculate three things:
The front wheels position when centered.
The front wheels position when turning.
The vehicles lateral acceleration.
The EBTCM runs a centering routine when the vehicle speed goes above 30 Km/h (18 mph). When the vehicle reaches 30 Km/h (18 mph), the EBTCM monitors the Steering Wheel Position Sensor inputs (Phase A, Phase B and Analog voltage) to see if the steering wheel is moving. If the steering wheel is not moving for a set period of time then the EBTCM assumes the vehicle is going in a straight line. At this point, the EBTCM looks at the analog voltage signal and reads the voltage. This voltage normally around 2.5V, is then considered the center position and the digital degrees also become zero at the same time. This centering routine is necessary to compensate for wear in the steering and suspension. Wear in the steering and suspension can result in a change in the relationship between the steering wheel and the front wheels. By running the centering routine the EBTCM can compensate for these changes by changing the digital and analog center position.
The EBTCM uses the digital input (Phase A and Phase B) from the Steering Wheel Position Sensor to calculate the direction the driver of the vehicle is trying to steer during an ABS event. This information is also used to calculate the vehicles lateral acceleration for Magnasteer®2.
Conditions for Setting the DTC
DTC C1281 will set when the digitally derived centered angle differs from the analog derived angle by 27 degrees or more for a period of 5 seconds.
DTC C1281 will set if the index pulse is not seen between ± 37 degrees or is seen between -185 degrees and -37 degrees or 37 degrees and 185 degrees of steering wheel travel.
DTC C1281 will set if phase A and or phase B are shorted.
Action Taken When the DTC Sets
Magnasteer®2 is disabled, ABS/TCS remains active.
Messages displayed on the DIC: Service Vehicle Soon
Conditions for Clearing the DTC
Condition for DTC is no longer present and scan tool clear DTC function is used.
Fifty ignition cycles have passed with no DTCs detected.
Diagnostic Aids
If the analog Steering Wheel Position Sensor input is missing then DTC C1288 will set.
If the Steering Wheel Position Sensor 5 volt supply or the Steering Wheel Position ground is missing DTC C1288 will set.
It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.
An intermittent malfunction can be caused by poor connections, broken insulation, or a wire that is broken inside the insulation.
If an intermittent malfunction exists refer to Testing for Electrical Intermittents in Wiring Systems.
I guess you tried to install Tech2win and got those virus warnings .
I have used Tech2win for years with no problem , but I use it on a dedicated laptop used only with motor related software ( I temporarely shut of my virus software(bitdefender) when I install the Tech2win software and activate the virus software after the Tech2win installation) Here is a good thread in the C6 forum about the Tech2win instalation with Dano523 is supplying very much good info
Here is some more info on which issues causing C1281
I have a 2000 (early ebcm) and it should be similar to previous years
Thank you for that screenshot.. that's exactly what I will need to view!
Yes, it was Tech2Win. Turning on your virus protection after installing malware is not going to help you!
It seems no one has been harmed by whatever is in that software, but I'm not taking the risk of being the first!
Thank you for that screenshot.. that's exactly what I will need to view!
Yes, it was Tech2Win. Turning on your virus protection after installing malware is not going to help you!
It seems no one has been harmed by whatever is in that software, but I'm not taking the risk of being the first!
Fred
You can always boot your laptop using a bootable Windows OS flash drive and install the software on it. This way you can't infect you hard drive and you will be able to run the tech2 app.
So I bit the bullet and purchased a used Tech2 clone....
I followed the procedure in the service manual for diagnosing C1281 (without RPO JL4)
- I ran the ABS diagnostic system check and it passed
- The only DTC code set in ABS/TCS is 1281 (1286 or 1288 are NOT present)
- I confirmed the analog voltage varies with steering wheel position
- I rotated the wheel until digital output indicated 50 degrees, noting the analog voltage is within spec (2.7 - 3.3V), Mine was 2.73V (pretty close to the edge)
- I confirmed the digital index pulse goes HIGH within +/- 37 degrees of centered
The procedure then instructs me to "Replace EBTCM".
Of course, this expensive.. And I'm not 100% sure this would solve my problem.
I eyeballed the EBTCM module and it "looks" fine.. I removed and reseated the cable harness going into it. It looked pretty clean inside for a 26 year old car!
(test drive coming later today).
I see several youtube videos of people opening and re-soldering the connections inside the EBTCM... ???
Anyone have any insight for me given the new data?
Thanks,
Fred
UPDATE: Drove about 50 miles.. No codes! Fingers crossed.
Just as a follow-up to future searchers... Reseating the EBTCM connector solved my issue.
I have driven the car 300 miles on numerous trips over the last month... and NO ISSUES!
Just another follow up here.. It's been 6 months and 1200 miles.. No codes whatsoever!
Re-seating the connector to the EBTCM 100% solved this issue. It's located on the transmission, in the rear. Easy to access and do.
1997 and 1998: C1281 - Steering position sensor
