I'm getting a C1287 and it's on the ever so popular 2000 C5 but I digress. So in "theory" the 1287 looks just for a uniform change in high/low of the digital phases of the SWPS correct? At least that is all the service manual has you looking at. It makes zero mention of checking the Digital SWPS Bias correction and digital SWPS position. These are what is appearing to go askew on mine (see pic). The odd thing is I just had the car split in half over winter to go through it. YES, It's centered and at ~2.50v while centered so that isn't the issue sadly. From what I've read this bias correction is the amount of change post centering routine. So in my 5 short test drive I had to somewhere have this thing throwing out a number 40 degrees different than something. I'm not sure what something that bias correction is correcting? Maybe the digital wheel position in degrees? Notice that @ 2.5V on the analog side i'm now at -74 deg on the digital side when it should be near 0. Oddly, when I run the SWPS test it is NOT more than a few degrees out. I suppose i need to see if the tech II can graph this as well as the wheel position over time. I know after centering the digital position was about 0 deg. while center but after a short drive i shot way askew. I'm going to double check C102 as I did have to remove that but I'd be shocked if that was the issue as when it came on I was in a very small sweeping curve which would not have dislodged any potentially lose connection. Plus there is a bunch of other systems in that plug for it to be the issue (outside air temp, AC, VSS, Oil temp, cruise, etc). As I said above, I also did a SWPS test and the analog and digital well well within the allotted 25 degrees for 5 seconds when I checked, in fact they were within 2 or 3 degrees.

Dave

 

Any input?

 

This reads like a question Bill Curlee would know the best response for. Far outside my - and I suspect many - knowledge base.

 

Hopefully he chimes in. This isn't a problem one can throw parts at.

 

There are two different sensors inside some of the SWPS. One is a resistive film that acts as a variable resistor and the other is an optical sensor of sorts. I'm not a SWPS expert but I have taken the simpler designed sensor apart and have see the wear marks in the resistive film caused by the wiper fingers repeated contact on the film. That's what causes the spikes in the output voltages when they go bad.

Cant tell you why you have the funky readings on the digital part of the sensor.

If it were ME, I would disconnect the SWPS connector and carefully (with a very critical eye) examine the male and female pins and see if everything is in proper order.
Look for spread female pins, corrosion, loose connector, damaged wires etc... Look at the male pins in the sensor (with a mirror) and see if they are in good shape.

I had an 06 Coupe and C6s had some serious SWPS issues. Part of the problem was poor contact between the male and female pins on the SWPS and cars SWPS harness connector. GMs fix for that was to insert a red plastic comb in the connector to force the female pins tighter against the male pins in the sensor. I had to physically bend my sensors male pins some to make better contact even after that stupid GM Comb was added. Problem solved after the male pin manipulation was accomplished.

What does the digital signal do when you go lock to lock on the steering wheel? Does it output random readings or count properly in degrees?



That's about all I can tell you..

Bill

 

I did reseat the swps plug at column last week just for the sake or argument even though that hasn't been touched in years. I'll also bend pins a hair to mitigate and potential intermittent connections thought I doubt that'd occur after sitting for winter. Last week I also ran the sensor full range both ways looking for any jumping bit it's as smooth as can be with is partially what baffles me. I've also disdained one of theses in the past hoping to come up with an easy way to get an operational and reliable one. Both digital and analog never seen to miss a beat but that bias offset is going nuts.

 

So without making a change the problem sort of rectified itself. I wonder what effect sitting for 6 mo. had to do w/ this. So for my reference if nothing else, the problem went away after driving a few times. I'm guessing the copper tracks the wipers ride on were just a bit corroded or needed to be cleaned.

Dae

 

I'm glad for you that everything is fine now, but that's interesting, to say the least, because those "wipers" and "tracks" are part of the potentiometer that provides the analog output and, per your previous tests, it was smooth and within ranges... It those contacts were bad the analog output would had had jumps here and there.

Could you please provide a screenshot from your Tech II for comparison purposes, after everything is fine, like the one you posted before?:

 

Sure give me a bit. In the past when I did that the Digital SWPW Bias Correction was withing a few degrees of 0 and digital steering wheel was 0 +/- 5 degrees when wheel was centered.

Actually, going to have to wait as I cannot run the centering routine in garage and my driveway was just re-coated so she's stuck in her stable for a while.


Dave

 

No worries. Looking forward to it

 

Question. When you say Digital SWPW Bias Correction, is that a function of the Tech 2 to sort of fine tune the the steering center? Mine trips codes at full left lock.

 

I'd have to go through the service manual again but it's not a function of the tech 2.

For those who wanted info on how it should look when it's working fine here it is. This is for my own info as i'll probably run into this next year and forget all this.

The ECM runs a centering test after it determines the wheels are going straight by noticing the digital phases not moving (Or moving in a way to indicate you are trying to remain straight) after x amount of minutes over x speed. At that point it determines that the digital steering wheel is 0deg and 2.50V. If the degrees varies more than x amount of degrees (Forgot what the manual said exactly on degrees allowable) at 2.50V it will throw a code. You'll see i'm at 2.46v and 4 deg on the digital side. I also included the special SWPS test you can do w/ wheels pointing straight which will compare the digital to analog. This must remain w/in x degrees also (Also written in service manual). nschiff, you'll have to rotate lock to lock w/ a tech 2 to see if you have a dead spot in your SWPS but I bet you may. Oddly mine came good again after a few drives and has been problem free ever since. I also had an issue a few times after going lock to lock but again,it's been acting fine the last 10-15 drives.

Dave




More details on the DTCs, centering routine, etc.

The Steering Wheel Position sensor has four outputs:

Digital output phase A
Digital output phase B
Index pulse (Non-Active Handling vehicles only)
Analog output
This information is used to calculate three things:

The front wheel's position when centered.
The front wheel's position when turning.
The vehicle's lateral acceleration. This is used for Magnasteer®2.
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 and/or Active Handling (RPO JL4) event. This information is also used to calculate the vehicle's lateral acceleration for Magnasteer®2.

The EBTCM runs a centering routine when the vehicle speed goes above 10 Km/h (6 mph). When the vehicle reaches 10 Km/h (6 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 tires when driving in a straight line. By running the centering routine, the EBTCM can compensate for these changes by changing the digital and analog center position.

Traction Control/Active Handling System On/Off Switch
The Traction Control/Active Handling On/Off Switch is a momentary on switch that allows the driver to shut off the TCS and Active Handling (RPO JL4) if equipped, for personal or diagnostic reasons, by pressing and releasing the switch. If the vehicle is equipped with Active Handling, the TCS/Active Handling On/Off switch can be pressed and held for 5 seconds; this places the system in Competitive driving mode. Competitive driving mode turns the TCS off but still allows Active Handling to be active. The switch is located in the center console.

Lateral Accelerometer (RPO JL4)




The Lateral Accelerometer is a self contained unit which uses a reference voltage of 5 volts. The sensor's operating range is -1.5 - +1.5G, resulting in an output range of 0.25-4.75 volts. Zero lateral acceleration results in an output signal of 2.5 volts. The EBTCM uses the Lateral Accelerometer along with the Steering Wheel Position Sensor, and the Wheel Speed Sensors to calculate the desired yaw rate. The EBTCM compares the desired yaw rate to the actual yaw rate that is received from the Yaw Rate Sensor. The difference between the actual yaw rate and the desired yaw rate is the yaw rate error. The Lateral Accelerometer is also used for the Bank Angle Compensation calculation. The Bank Angle Compensation calculation is an important part of the Active Handling algorithm.

Yaw Rate Sensor (RPO JL4)




The Yaw Rate Sensor is a self contained unit which uses a reference voltage of 5 volts. The sensor's range is -75 - +75 degrees/second, resulting in a signal proportional output of 0.25-4.75 volts. Zero yaw rate is 2.5 volts. The EBTCM uses the Yaw Rate Sensor to determine the vehicles actual yaw rate to compare to the desired yaw rate. The difference between the actual yaw rate and the desired yaw rate is the yaw rate error.

Brake Pressure Sensor (RPO JL4)