DeeGee

No joy in General so trying this in C5 Tech

I'm happy with how the the AH system works and I've already had the EBCM replaced so this one got me stumped.

I'm getting AH trips which are resetting once I restart the car. The caption comes up, TCS stays in but AH trips. The trip always occurs when I'm stationary. Quite often I get a shimmy from the AH under gentle braking followed by the associated AH caption on the DIC just before it trips out. I've been using the Vert as a DD for a few weeks and often it trips at the same road junction.

I have a C1287H steering sensor rate malfunction
I also have a B2587H, B2592H and B2593H which are Column Lock/Unlock Drive A and Drive B faults. I've never heard of these and I have an A4 which doesn't have a column lock. My battery is good. My car is garaged so the grounds are clean and undisturbed.

My thought is the steering wheel positon sensor is the culprit but the trip always occurs when Im stationary and the steering wheel is straight and not moving.

Can anyone cast any light on why? How does the sensor get its information. is it purely electrical? Whats the interaction between the sensor on the hub and the sensor on the steering wheel. Is it all processed at the BCM?

I'm thinking the best start would be to pull the sensor connectors at the hubs and try some lubrication.

Any ideas?

Bill Curlee

If your car is NOT correctly aligned, it could have an effect on AH.

Is your steering wheel completely centered when your on a straight level road while your going straight ???? If it is off center, that could be the issue. If the steering wheel input is to the right or left due to misalignment and the car is actually going in the intended straight direction, the EBTCM is going to pulse the brakes on one wheel to cause the car to go in the actual incorrect steering wheel direction. You will have a pulsation in the brakes caused by the EBTCM /BPMV

You could also have an accelerometer wiring issue or a bad sensor. There are TWO sensors. One in the passengers foot well by the inboard seat rail and one under the HVAC control module on the center console. You can easily check out the integrity of the sensor and sensor wiring and connector.


If the accelerometer is telling the EBTCM that the car has movement in one axis or the other (and it really doesn't) it will use brakes to correct for it.

BC

DeeGee

Thanks for the input Bill

The steering wheel is perfectly straight so I guess that brings me down to one of the two sensors.

BlackZ06

DeeGee,

The Active Handling System is pretty clever. AH is part of the Electronic Brake Control Module (EBCM) which also controls the Anti-lock Brakes, Traction Control, and rear brake proportioning. Active Handling uses inputs from the following sensors to decide if/when/how to intervene ....

Yaw rate sensor - located in the vehicle cabin, it senses how quickly the vehicle is turning (rotating). For example, a Left turn of 90 degrees executed quickly in just a few feet is a high yaw rate, while the same 90 degree turn executed over a long distance and time (such as a Motorway curve) produces a low yaw rate.

Accelerometer - also located in the vehicle cabin, determines, basically, what side G force the car is experiencing. Using the Motorway example, the accelerometer will detect a lower G force if I drive through the curve at 40 MPH than it would if I drove the same curve at 120 MPH

Steering Wheel Position Sensor (SWPS) - located on the steering column, it determines what "angle" the steering wheel is turned at. When you first start the car, the AH system "calibrates" the SWPS when the car is driving straight (the accelerometer and yaw sensors are reporting ZERO ... the EBCM figures the car is going straight) at over 6 MPH for at least 10 seconds. The SWPS has an "A" side and a "B" side for its output. The two signals are basically set to ZERO when the SWPS is calibrated, and then the two signals will change (one getting stronger, the other weaker) as the wheel is turned. Effectively the steering column has a magnet in it and the two sides of the sensor are simply reporting how strong the magnetic field is on their side. The EBCM can figure out which way the wheel is turned, and how far it is turned, by these two signals.

Wheel Speed Sensors - located in each wheel hub, they ... duh ... report individual wheel speeds to the EBCM.

Let's look at how this works ....

1) You're on the Motorway, coming up to a sweeping left curve, and the road is wet and even icey. You turn the steering wheel a certain amount to the left for the curve. The EBCM checks and says ... OK ... he's got 10 degrees left angle on the wheel, and the road speed is 70 MPH, I should see X amount of yaw and Y amount of G forces.

If that is what those sensors report, the EBCM will not invoke AH.

But let's say that because the road is slick, you get understeer when you turn the steering wheel ... the wheel is turned, but the car is not responding to your input .. it is "pushing" straight ahead. The EBCM will see that the yaw and accelerometer readings are too low. It will invoke AH and apply braking to the Left Front wheel ONLY. This will tend to both bring more of the cars weight to the front tires because of deceleration (helping them grip) and it will help the car "rotate" around the front left tire, causing the car to yaw, or turn, in the direction you want it too.

Let's look at one other example ... you go into the same curve, and the car is tracking around the curve just fine. Suddenly you hit a HUGE ice patch ... and the car continues to yaw (rotate) but now it is no longer actually following the path of the curve, but is moving in a straight line.. We've all seen video/film of a car on ice doing slow "pirouettes" (spins) while sliding down the road .... The EBCM will see the yaw rate as still correct, but the accelerometer reading will drop to zero ... the EBCM will know the car is in a slide, and depending on your steering input (and the wheel speed sensors) it will decide where to apply braking to attempt to help you regain control of the vehicle.

In your case, since you have a C 1287 posted by the EBCM, the most likely culprit is the SWPS. A C1287 sets if the EBCM sees "weird" input from one or both "sides" of the sensor. For example if the sensor input shows you are turning the steering wheel FASTER than 1,100 degrees of angle per second, the DTC will set. ANother "trigger" for this DTC is if the A and B side of the SWPS are out of agreement by more than 20 degrees of steering angle.

The SWPS could report false readings even if you are stopped ... so I would venture that the SWPS is the likely culprit if there are no other EBCM DTCs set.

DeeGee

Awesome description thanksd for taking the time to post.

That sounds logical. Any idea what the Column Lock/Unlock Drive A and Drive B codes are? Are they monitoring the output of the SWPS in some way? If so, that makes a lot of sense

BlackZ06

Unfortunately (or fortunately - depends on your point of view) the A and B sides of the column lock have NOTHING to do with the SWPS and its A and B sides.

The A and B positions of the lock motor are equivalent to LOCK and UNLOCK positions ... if the BCM wants to LOCK the column it commands the A relay to ACTIVE and the motor drives the column lock into the steering column. If the BCM wants to unlock the column it commands the B relay to ACTIVE and the motor withdraws the locking pin from the column.

If you look at the electrical schematic for the steering column you realize that, first, the column has a lot of functions built in ... telescoping (if installed) electrics, the column lock system, and even though the ignition switch is not actually on the column, the electrical system treats it as if it was part of the steering column (probably because the ignition switch and column lock are closely inter-related). The second thing you realize is that either the engineers who designed the electrical system were geniuses, or they were stoned out of their gourds on acid when they put this together ... I vote for the acid explanation ....

Treat the Column Lock issues COMPLETELY seperately from the SWPS issues ..... so far in this rats nest of wiring diagrams I can't see where one would impact the other ....

Bill Curlee

BLACK ZO6

You have this information nailed down to a T!! Well done AND VERY ACCURATE!!!

BC

BlackZ06

Bill,

Thank you,

Steve

DeeGee

BlackZ06 and Bill Curlee on the case. Nothing can go wrong

Thanks for the advice Gents.

Looks like I may have been looking at a "Pull Key Wait for 10 Seconds" if I didn't have an A4 with no column lock.

I cleared those codes and no reocurrence after a week .

The C1287 hasn't come back either and I've been driving every day again this week. No trips in that time but the AH is still very sensitive particularly under light braking. Firm braking and its just fine. I'll watch it for a while and see if I can work out any other trend. Its very strange that it often happens at the same junction. It's almost as though a particular set of turns or decelerations causes the trip.

Thanks again for all the help. If you're ever over this side of the pond I have a pint of Boddingtons with your name on it

DeeGee

Just an update on this problem. I have some vacation coming up so I may delve in a little more

The problem seems to be only showing in certain situations but it is getting a little worse. The AH generally is more twitchy than it used to be. It also cuts in under far less extreme conditions than it used to.

The trips are occurring on dry roads. I had one trip this week where the AH message was flashing up intermittently. The caption would light and disappear almost straight away but no check gages. After 3 or 4 nuisance wanings the AH would trip out but the TCS stays in. It throws a C1287H and resets once the car is restarted.

It also shows itself regularly at the same set of lights. Normal driving its fine; through the twists and turns of the back roads without problem. Approaching the same sets of lights after a 3 mile straight run with light braking to a stop. After about 10 secs stationary the AH trips out. the steering wheel is aligned and the wheel is not turning and straight when the trip occurs.

From BlackZ06's description I'm working down towards an accelerometer issue. What I cant understand is why the SWPS would report any signal under light braking with no turn input. Thts is unless the sensor is feeding in a signal and with the car straight and stationary, the EBCM says you cant be turning and trips out.

Does my logic check out?

Whiteonrice

I was just surfing, reading etc. before I went to bed here in So Cal. It must be frustrating to be over there trying to diagnose your own problem and then if you (maybe) figure it out having to wait forever to get the (maybe) correct parts. Best of luck to you.

Used to fly a Gulfstream GII years ago that had an Inertial Navigation System that used accelerometers. Had to park and leave it motionless for an ungodly amount of time and put in the current coordinates. I think you could only put three or four waypoints in it. Things have sure got a lot better in the last twenty years.

Rick

BlackZ06

Your logic makes sense ...what your car is doing does NOT !!

I'm still leaning toward the SWPS being the culprit. The accelerometer and yaw sensors have their own diagnostics run by the EBCM, some diags are run when the car is standing still, others run when the car is moving. The EBCM should throw a C1284 or C1285 if it detects a problem with the lateral accelerometer, for example, so if the ONLY code you're getting is the C1287, it would SEEM that the SWPS is the issue, but then we've all played the game of "find the electrical gremlin causing THIS problem" .....

The system resets every time you start the car, so it is understandable that everything comes up fine until the gremlin appears and shuts down the AH.

What is REALLY weird is that the AH fails at the same traffic light apparently consistently. Turning the steering wheel while stopped is "allowed" by the EBCM. It is considered a "normal" manuever when parallel parking the car, for example, so that shouldn't be an issue.

Is it possible there is a strong radio/radar source near that traffic light ?? Possibly a strong electro-magnetic field is interfering with the sensor (one of those speeding cameras triggered by radar ... you're parked outside GCHQ ??? - I know my radar detector goes NUTS the second I crest the Tehachapi Mountains and stays lit all the way across the Mojave Desert ... Thanks to (I suspect) Edwards AFB ... ) OR possibly the road has a steep camber or tram lines, or something else affeecting your steering input?

I'm intrigued by this one .... PLEASE keep us posted !!!!

DeeGee

Now theres a thought. There is a speed camera only 50 yds up the road at that spot. Its bi directional but often pointed at the junction. Mind you, thats not the only place I've had a trip but its by far the most common. I'll get the radar receiver out next time I'm passing and see if there's a strong signal. Mind you, I work at a major airbase and the airfield radar doesn't cause any problems

BTW spent many happy hours at Edwards and I think I can guess on a few things that may be causing your receiver to go off.

BlackZ06

Yeah, but my bet is you'd have to shoot me BEFORE you could tell me what they are

DeeGee

How did you know?

DeeGee

Guys I checked at the spot where the speed camera sits and the spillover isn't that bad so its not that which is causing the problem.

Its getting worse and trips out most times I drive over about 25 miles now. Still a C1287H

I've been trying to work out what causes the trip. Its definitely related to the brakes. If I brake gently the AH will be jittery and throw an AH caption on the DIC but stay engaged. After short while I'll get a momentary DIC AH caption but again it will stay engaged. Eventually the system will trip out. Normally I'll be going straight when it happens. If I brake firmly it doesn't happen. It alsmost takes that first gentle application of brakes to start the process going.

How does the brake pressure cause this. in other words how does gentle application cause the sensors to get confused? Could the fact that I need new pads be a problem?

I plan to get into the hubs and try BCs clean up of the connectors as a first step.

Bill Curlee

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

TheDVS1

Fascinating thread. I've learned a lot.

Logic would dictate that if the problem seems most apparent under braking that it'd be a wheel speed sensor. Perhaps you've got one that's sending a crazy signal? But then again, wouldn't it trip a code?

Great thread, but I hope you get it fixed soon!

timemender

Rear brake proportioning controlled electronically through the EBTCM on 2001 and newer only.

Bill Curlee

DSV1

I had a very similar issue on my 02 ZO6. The DIC code for the right front wheel sensor did trip. Thought, Ok,,this is an easy fix. I paid the man for a new sensor, installed it and WHAM,,,,,,,NO CHANGE!

I have disassembled numerous wheel speed sensors and they are pretty much bullet proof!









If you damage the wires or the connector, that would one of the rare things that would put it out of commission. The rotor is a PM magnet that is molded into a toothed reluctor wheel that rotates inside the pick up coil stator and the result is a AC signal that gets larger as the speed of the wheel increases. At slow speeds your talking about millivolts. The connections between the sensors and the EBTCM have to be 100%. Thats where 90% of the WSS problems originate. The male to female connectors suck. There easily damaged by vibration and just disconnecting and reconnecting the connectors. I learned to HATE Delphi! Their quality is sub par in a LOT of things!

Here is a close up of a good and bad wheel speed sensor front wheel jumper harness female connector! This is the problem with most of the bad sensors.

Jumper cable:



New connector is on the LEFT bad connector on the right:



The correct way to figure out if you have a female pin that is NOT making the correct connection is to purchase a MALE Pin of the same size pin end and insert it into the female pin. If it has a tight grip, your all set. If it falls out or is very loose,,,,you need to replace the pin or connector.









BC

BC