Intermittant ABS issue
27-08-2009, 09:11 PM
#1
OCD Victim
Thread Starter
Intermittant ABS issue
Time to post a little question for everyone...
My 4x4 1992 DOHC Saff has just started with an intriguing ABS issue. About 2 weeks ago, I had both red and yellow dash lights coming on in the dash. Checked the reservoir and the fluid level had dropped about 1 inch max. Went looking and found that the passenger rear caliper bleed nipple had managed to wind undone slightly, just enough to allow a little bit of fluid to weep when the brakes were pressed, but not enough to drop any fluid on the wheel.
Tightened that up and refilled the reservoir accordingly and immediately lost the red warning light (no surprise). But, I still had a "weird" brake pedal.
So, last weekend I put a new set of rear pads in (they were wearing down anyway) and bled both rear brakes out. Fine. But, I still randomly get a weird brake pedal and yellow ABS light coming on.
An example: start the car and the ABS light does its self-test before going out in under 20 seconds. Drive down the road and it will drive fine until a random moment when the brake pedal starts to pulse as if either the ABS is engaging or the pedal is pumping up. The next time the car gets to 20mph or above, the ABS light comes on as if the system has detected an ABS sensor fault (even though it has passed its own self-test earlier in the same drive period). The light will stay on until you turn the ignition off. You can restart the car immediately and the problem will go away until another random moment.
At no time does the car attempt to lock-up under braking, or anything similar.
The fluid level is good, all the connections to the sensors, pump, reservoir cap, etc... are good, clean and still coated with their protective grease.
I have not performed an ohms check on the sensors yet (will do this over the weekend when I have time). The fluid is DOT 5.1 as it has been running for over 7 years and is bled out every time I change front or rear pads (normally every couple of years or 15k, whichever comes first).
I have spare ABS valve blocks, reservoir caps, ECU, etc.. but am not sure on sensors themselves.
The wheel bearings seem okay and the original dust covers are over all four driveshafts to protect from dust ingress.
Thoughts on this one?
My 4x4 1992 DOHC Saff has just started with an intriguing ABS issue. About 2 weeks ago, I had both red and yellow dash lights coming on in the dash. Checked the reservoir and the fluid level had dropped about 1 inch max. Went looking and found that the passenger rear caliper bleed nipple had managed to wind undone slightly, just enough to allow a little bit of fluid to weep when the brakes were pressed, but not enough to drop any fluid on the wheel.
Tightened that up and refilled the reservoir accordingly and immediately lost the red warning light (no surprise). But, I still had a "weird" brake pedal.
So, last weekend I put a new set of rear pads in (they were wearing down anyway) and bled both rear brakes out. Fine. But, I still randomly get a weird brake pedal and yellow ABS light coming on.
An example: start the car and the ABS light does its self-test before going out in under 20 seconds. Drive down the road and it will drive fine until a random moment when the brake pedal starts to pulse as if either the ABS is engaging or the pedal is pumping up. The next time the car gets to 20mph or above, the ABS light comes on as if the system has detected an ABS sensor fault (even though it has passed its own self-test earlier in the same drive period). The light will stay on until you turn the ignition off. You can restart the car immediately and the problem will go away until another random moment.
At no time does the car attempt to lock-up under braking, or anything similar.
The fluid level is good, all the connections to the sensors, pump, reservoir cap, etc... are good, clean and still coated with their protective grease.
I have not performed an ohms check on the sensors yet (will do this over the weekend when I have time). The fluid is DOT 5.1 as it has been running for over 7 years and is bled out every time I change front or rear pads (normally every couple of years or 15k, whichever comes first).
I have spare ABS valve blocks, reservoir caps, ECU, etc.. but am not sure on sensors themselves.
The wheel bearings seem okay and the original dust covers are over all four driveshafts to protect from dust ingress.
Thoughts on this one?
28-08-2009, 05:51 AM
#2
OCD Victim
Thread Starter
Okay, test drive time.
Have just driven to work. Started the car, let the ABS perform its self-test as per always. Lights go out. Drive off down the road and am doing approx. 40mph for about 3 miles. Slow down for a set of traffic lights (to about 25mph) and then accelerate (reasonably hard to about 3/4 throttle) as the lights change to green. Look down @ the speedo and the ABS light comes on while I am accelerating around 35mph.
The light then stays on for a further 3 miles with no adverse braking conditions.
I pulled to a stop around the corner from work and switched the engine off. Waited 3 seconds and then restarted the engine. The ABS performed its self-test and the light went out within 2-3 seconds. Drove down the road around 20mph and the ABS light started coming on and going off about 3 times in 300-500 yards before going out just before I stopped.
Upon stopping, the pedal pulsed as if the ABS was kicking in, but no light on the dash. Parked the car and checked the pump and reservoir. Reservoir is @ its normal level of just over the max. mark and the pump was cold to the touch.
Have just driven to work. Started the car, let the ABS perform its self-test as per always. Lights go out. Drive off down the road and am doing approx. 40mph for about 3 miles. Slow down for a set of traffic lights (to about 25mph) and then accelerate (reasonably hard to about 3/4 throttle) as the lights change to green. Look down @ the speedo and the ABS light comes on while I am accelerating around 35mph.
The light then stays on for a further 3 miles with no adverse braking conditions.
I pulled to a stop around the corner from work and switched the engine off. Waited 3 seconds and then restarted the engine. The ABS performed its self-test and the light went out within 2-3 seconds. Drove down the road around 20mph and the ABS light started coming on and going off about 3 times in 300-500 yards before going out just before I stopped.
Upon stopping, the pedal pulsed as if the ABS was kicking in, but no light on the dash. Parked the car and checked the pump and reservoir. Reservoir is @ its normal level of just over the max. mark and the pump was cold to the touch.
28-08-2009, 09:38 AM
#3
I reckon you've got a sensor cable that's perished and earthing on the body, as they're routed through the front chassis rails. Mine did this - I wound black tape around the broken insulation as the coaxial cable inside was OK other than being exposed.
31-08-2009, 08:32 PM
#5
OCD Victim
Thread Starter
Well, looks like it might (hopefully) be fixed.
Took the front ABS sensors out (they came out remarkably easy as they have not been touched for 17 years :shock: ) and one had a little bit of rust particles in the teeth of the sensor ring and the other side had a small piece of the resin disc that sits on the face of the sensor broken off and wedged in the gap.
I am guessing that the little piece randomly "picked up" on the teeth and moved in front of the sensor, fooling it into thinking that the wheel was not moving.
The sensors were all tested, along with a "wiggle test" to check for breaks and the fronts both registered 1.12K and the rears both 1.09K.
The test will be tomorrow as I will use it for work and see how it works.
I have left the rear sensors alone in the hubs for now for the purpose of testing. If the problem is still there, chances are it will be the rears.
Took the front ABS sensors out (they came out remarkably easy as they have not been touched for 17 years :shock: ) and one had a little bit of rust particles in the teeth of the sensor ring and the other side had a small piece of the resin disc that sits on the face of the sensor broken off and wedged in the gap.
I am guessing that the little piece randomly "picked up" on the teeth and moved in front of the sensor, fooling it into thinking that the wheel was not moving.
The sensors were all tested, along with a "wiggle test" to check for breaks and the fronts both registered 1.12K and the rears both 1.09K.
The test will be tomorrow as I will use it for work and see how it works.
I have left the rear sensors alone in the hubs for now for the purpose of testing. If the problem is still there, chances are it will be the rears.
Thread
Thread Starter
Forum
Replies
Last Post