Hi Guys,

Running a 2001 MN6. After tripping the check ABS sensor warning I found that my front right wheel hub wheel position sensor harness was completely ripped off the wheel hub. So I replaced the hub (as well as the drivers side front). Sent the EBCM to ABS Fixer as well to have it checked out. Came back "A-OK" (it was rebuilt a few years back). After resetting the codes - the car drove fine for a few weeks.

Then 2 days ago - the ABS and Traction Control warning started to come on with EXTREME frequency. e.g. ABS every time I brake and Traction Control intermittently/randomly - even under normal (non/slip/yaw) driving conditions. However - no error codes are coming up in the DIC. Odd.

If I turn the traction control system off I do not get the traction control issues but the ABS systems still goes bezerk every time I brake (again with no error codes).

Any thoughts where to start on this one?

NOTE: Not that it would matter, but I did also replace the shocks (all four corners) as well as brake pads and rotors (and flushed & bled the brake system) when I changed the wheel hubs. Tires are a bit old... would any of this matter?

Cheers,
Dennis

 

maybe still air in the EBCM needs to be bled with the Tech 2 ???

 

I recently did a full brake job on my 4runner and also replaced one of the front ABS sensors (the other had been replaced a few months ago) and now - when coming to a stop (at about 10mph) - the ABS "chatters" for a moment the pedal drops about an inch. I found this on a GM forum which seems to explain my problem - perhaps some clues in here for you....

Condition
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction
Measure AC voltage and clean the wheel speed sensor mounting surfaces.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual (SI Document ID #899664).

Disconnect both the front wheel speed sensor (WSS) connectors at the frame and harness.

Place a Digital Volt Meter (DVM) across the terminals of each WSS connector.

Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual. Plug the WSS bore in order to prevent debris from falling into the hub during service.

Clean the WSS mounting surface on the hub to remove any rust or corrosion using a wire brush, or equivalent.

Important
Make sure that the sensor sits flat on the hub. Check the sensor flange against a straight edge to ensure flatness. If the sensor flange is distorted, replace the sensor.

 

Then 2 days ago - the ABS and Traction Control warning started to come on with EXTREME frequency. e.g. ABS every time I brake and Traction Control intermittently/randomly - even under normal (non/slip/yaw) driving conditions. However - no error codes are coming up in the DIC. Odd.


If you have DIC messages indicating that the ABS and or Traction control is active, you usually wont have DTCs. AH/TC active AH active= Something is telling the EBTCM that you have steering input for "X" direction and the car is going in "Y" direction. TC Active is telling you that you have rear wheel slippage on one wheel or both.

Its trying to correct for wheel slippage or YAW error. The Steering Wheel Position Sensor going bad can cause RANDOM AH issues and not throw DTCs until it gets to the point that the system is UNHAPPY!

That said HOWEVER, something is wrong to make the ABS and TC active under NORMAL conditions.

8VETTE7 is spot on. The EBTCM clears the error code/s at ignition OFF and does a operational startup sequence and test at ignition ON.

If there are DTCs for that system, you need to interrogate the EBTCM when it powers on and or when it has an issue or error message.

BC

 

Thx Guys.

I am not sure that this is related to the EBCTM. My reasons:

1. I do get messages that ABS and/or active handling are active when braking or taking corners. However I get no error codes. There are no codes to read.

2. When I turn the traction control OFF, I still have ABS issues (every time I brake) but I witness no traction control issues (e.g. I believe the steering wheel sensors, etc. are disabled when traction control is off so I am expecting that wheel braking is no longer activated when steering input/yaw is not as expected from the computer)

3. I have brand new hubs on the front wheels. The wheel hubs include the wheel speed sensors. They are "closed" units and there is nothing to clean here... you just bolt the hubs on and pug the wheel speed sensor cable into the car's harness.

4. I am running the stock wheels and tires (245/45-17 in front and 275/40-18 in the rear)... albeit the tires are a little old and ready to be replaced. The car ran fine for 2-3 weeks after installing the new wheel hubs...

I am thus suspicious of the following:

A) Could one of the new wheel hubs (and the wheel speed sensor therein) I installed be bad?
B) Could one or more of the rear wheel hubs/speed sensors (which I did not replace) be bad?
C) Could my tires be sooo bad (although they do not appear to be THAT bad) that slippage under cornering and braking is legitimately causing the ABS/Traction Control to intercede (correctly)? I have been driving in California dry conditions... so...

I am thinking this is not a "computer issue" as much as a "sensor" (slippage is not occurring but the sensor is incorrectly indicating that it is) or "data" (actual slippage is occurring) issue.

Any thoughts? Am I going down the wrong path here? Anyone know what voltage readings I should get on a GM wheel speed sensor? I suppose I can test those as jjc508520 mentioned...

-Dennis

 

One more question... I am not sure what akapounder is mentioning when he says "air in the EBCM?" Do you mean air in the brake lines (e.g. brake system still needs to be bled)? Could air (or dare I say - water!!??) in the brake system cause the EBCM to go wonky like this? I can quickly re-bleed/flush the brakes... but I do have a good solid/fade free brake pedal right now. Nothing leads me to believe that I have air/water in the lines...

-Dennis

 

WSS issues will always pop a DTC.

BC

 

Thx guys. Will try to disconnect the steering wheel position sensor today and see what happens. Question - where is the harness for this? Never been in this part of the car... so where is easiest place to disconnect? Do I need to remove the dash to get to it?

-Dennis

 

I doubt the steering wheel position sensor will cause ABS issues as it isn't used in the ABS algorithms. If it isn't used then it doesn't matter whether it has a shorted circuit, an open circuit or a noisy circuit. Disconnecting it will prove that quickly. I know the steering sensor was used to control TC on the 97s (had that issue with mine), however, they changed the system in 2001 and I am pretty sure only the Active Handling function used it from then on.

The EBCM doesn't have any fluid in it but the BPMV which it is attached to does have brake fluid. Air can get into the module but it results in the same issues you get if air gets into other parts of the system. The brake pedal will feel spongy and will take some pumping to get the car to stop properly.

ABS is initiated by the EBCM detecting wheel speed variations that indicate one or more wheels are slipping. When it activates ABS it does so by releasing brake pressure at the wheel that isn't turning properly. When TC activates it will react slightly differently if the car is going slow or fast. At slow speeds it might choose to activate a brake on the rear axle or activate both the brake and torque reduction. At higher speeds it will activate torque reduction first since it can do that faster, followed by brake application if the torque reduction doesn't reduce the slippage. TC is mainly activated by differences between the front wheel speeds and the rear wheel speeds as well as differences between the rear wheel speeds. From my experience it activated much sooner with variances between the two rear wheels than between the front and rear. As long as both rear wheels spin about the same it will let you spin them up to a point but if one of those rear wheels slips more or less it will clamp down.

It sort of sounds like you have a problem with the wheel speeds but it isn't severe enough to set off a DTC. I would be looking for bad connections at the connectors where the sensors connect to the car's harnesses and where the harness attaches to the EBCM. Also check voltage and ground connections. Another thing that can happen is electrical noise that gets conducted into the harness going to the EBCM. Has somebody moved wires around under the hood? Has somebody installed different spark plugs? Any other underhood electrical changes?

Bill

 

Thx 8VETTE7. I disconnected the SWPS easily and unfortunately... my problem did not go away. ABS engaged every time I braked. Dry sunny weather an normal driving conditions. The behavior was the same as when I turn traction control off. So, I am thinking Bill Dearborn might be on to something in his post...


Anyone else have thoughts at this point?

-Dennis

 

The WSS have very crappy connectors. The FEMALE PINS in the connectors spread apart and lose connection at the slightest vibration and cause errors and issues. Until you do a pin push/pull test by inserting a male pin into the female pins, you will not know if the connections are good or not.

The Front wheel Jumper Harness is a PRIME contributor to this issue

 

Thx Everyone.

Had to abandon repairing the Vette for the last 2 weeks due to work. Now back at it.. and an update:

1. Steering Wheel Position Sensor is disconnected. I still have ABS issues EVERY time I brake - regardless of driving conditions. No traction control issues though.

2. When I shut off the engine, a loud electric motor runs/cycles for 10+/- seconds. the motor sounds like it is near the master cylinder/power brake booster... but not sure.

3. As a reminder - I only replaced the front wheel hubs (and wheel speed sensors). Could this be an issue if the front sensors are not "the same" as the rears?

QUESTIONS: Is there a proper brake bleed procedure given the ABS on this car? I just flushed the system and bled them like I do every other car. Maybe air in the system? Does anyone know the voltage, etc. I should get if I plug a test tool into the wheel hub speed sensor and rotate the wheels? I owuld like to test of the wheel speed sensors are the problem.

thx,
Dennis

 

https://www.corvetteforum.com/forums...h-2-bleed.html

 

Thx akapounder. I don't have a tech 2. Any advice on another way to bleed the system... or will I always be dealing with potential air in the EBCM? I do have a Mityvac... but didn't use it on the bleed last time.

-Dennis

 

GM came up with the Tech 2 Auto Bleed for a reason, that said some here have done it another way by making the ABS apply. I didn't get into the thread because of my having the Tech 2 (best 300 I have spent for the vette) don't know if you read my whole thread on the bleed, but my fluid was a bit murky and after the bleed crystal clear !!

 

Thx. I was afraid you would say that. I may move to a C7... and the Tech 2 indicates that it doesn't support the C7, so this would be a wasted purchase. Might just find a local shop that has the GM scan/tool and can do the bleed properly.

Cheers,
Dennis

 

maybe someone near you has a Tech 2 ???

 

did you replace the wheel bearings yourself or have a shop do them. I have had a 2 friends have a shop do them and they did not torque the bolts correctly and one of the three bolts came loose, both had ABS/TC lights come on. One of them went to an auocross and he finally came up with a code C1225. He came to my house and we found one bolt loose and the other not up to 97lb of torque. Did the quick fix of torque the bolts but the problem did not disappear. Pulled the Wheel bearing off and found the bearing cap was coming off. Tapped the cap back on, replace the bearing torqued everything and no he has no problems at all. Told the other person about the problem and found two loose bolts on his bearings. We told all are friends to avoid going to that shop in the future.

 

Hi Guys,

Only get to work on the Vette when I get free time... so been a few days... anyway... I bled the system using a tech 2 and it sucked up three bottles of DOT 3. plugged the Steering Wheel Position Sensor back in. Put new tires on the car and swapped out the rear wheel hubs. Reset all codes. Test drive at the the shop went well... so tire shop called me to pick up the car... and then on the ride home BAM! ABS and Traction control going bonkers. Traction control going off just driving down the road at 25 mph (no braking). ABS going off at every stop. So - I shut of traction control - and life was OK... except ABS still going off every stop. I have absolutely NO fault codes. What now? Bad brake booster? Still air in the system? Bad ABS Module?

 

Thx. The wheel hubs/bearings are a single assembly. See here.

I had a good shop put them on but they were torqued to spec. I *think* the problem is with the braking / ABS. E.g. With the Steering Wheel Position Sensor disconnected I get no traction control issues... but I do get ABS issues every time I brake. I am truly baffled. Bad brake booster?

-Dennis