ABS speed sensors
08-30-2013, 11:55 AM
#46
Rennlist Member
No problem mentioning the obvious mate. Yes it's full but will be doing a bleed this weekend to ensure there's no air lock in the pump - adrians book metions a stuck return pump can fire the warning when moving off. I'm wondering if there could be air in there when the pump was removed during the fitting of the new floor?
08-30-2013, 05:42 PM
#47
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I am having the same situation currently with my 1993 RSA. Initial start up no ABS light, once the vehicle starts moving around 5 mph the light and warning tone go off. It appears that I only have front brakes as I can lock up the front brakes (no ABS reaction) and I can see no brake dust or wear on the rear rotors.
The 4 sensors read 1.047, 1.027, 1.039, 1.053 at the abs box harness end. The relay on the ABS pump and the relays in the fuse box all seem to check out as when I apply power from the battery to terminals 86/85 I achieve continuity across terminals 30/87 and hear an audible click.
I have cleaned the three grounding points in the trunk and each ground at the wheel sensors.
I have installed a new battery for ample power to the system.
I have a hammer (KTS301) and am getting fault code A01 under the ABS 5 / ABD section and fault code A00 under the ABS 5 section. My factory manual does not cover these codes or I am missing this section. I also am having zero luck finding any OBD1 code cross reference anywhere.
I initially pressure bled the brake system with success (I thought), but now I am wondering if I missed a procedure to eliminate any air in the ABS pump. I bled the system with the engine / ignition off. I recently jumped the pump relay and the ABS pump made noise.
Is there a proper procedure to remove air from the pump?
I read a couple posts that Adrian has outlined a procedure, but did not know which book of his to purchase that covers this.
I also called Bosch and spoke with their tech line trying to get a fault code cross reference list for the ODB1 units. They mentioned that since the hammer was an OE supplied tool one would have to contact Porsche directly by submitting a help desk request thru the dealer. I'm not confident that an individual with a hammer would get any response from a dealer network help desk request.
I also read a post referencing the clock has power running thru it that could contribute to this problem from "cold solder"joints. I don't think all of my clock lights illuminate so this is something that I will eliminate shortly.
Any help with the ABS bleeding / fault code cross reference would be greatly appreciated.
Thank you in advance.
Tom
The 4 sensors read 1.047, 1.027, 1.039, 1.053 at the abs box harness end. The relay on the ABS pump and the relays in the fuse box all seem to check out as when I apply power from the battery to terminals 86/85 I achieve continuity across terminals 30/87 and hear an audible click.
I have cleaned the three grounding points in the trunk and each ground at the wheel sensors.
I have installed a new battery for ample power to the system.
I have a hammer (KTS301) and am getting fault code A01 under the ABS 5 / ABD section and fault code A00 under the ABS 5 section. My factory manual does not cover these codes or I am missing this section. I also am having zero luck finding any OBD1 code cross reference anywhere.
I initially pressure bled the brake system with success (I thought), but now I am wondering if I missed a procedure to eliminate any air in the ABS pump. I bled the system with the engine / ignition off. I recently jumped the pump relay and the ABS pump made noise.
Is there a proper procedure to remove air from the pump?
I read a couple posts that Adrian has outlined a procedure, but did not know which book of his to purchase that covers this.
I also called Bosch and spoke with their tech line trying to get a fault code cross reference list for the ODB1 units. They mentioned that since the hammer was an OE supplied tool one would have to contact Porsche directly by submitting a help desk request thru the dealer. I'm not confident that an individual with a hammer would get any response from a dealer network help desk request.
I also read a post referencing the clock has power running thru it that could contribute to this problem from "cold solder"joints. I don't think all of my clock lights illuminate so this is something that I will eliminate shortly.
Any help with the ABS bleeding / fault code cross reference would be greatly appreciated.
Thank you in advance.
Tom
08-31-2013, 04:44 AM
#48
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08-31-2013, 06:21 AM
#49
Nordschleife Master
Thread Starter
Thanks for posting Tom. Since it looks like our problem is identical, hopefully we'll find the solution soon.
Thanks for the link Blomman. It shows how complex the C4 system is if you need to bleed. Tom's RSA and my C2 only have bleed nipples on the calipers and the clutch slave. So I guess the only bleeding process for the ABS pump is to bleed through a caliper. I'm going to be trying that approach with the left front first (appears to be shortest path to the pump).
Thanks for the link Blomman. It shows how complex the C4 system is if you need to bleed. Tom's RSA and my C2 only have bleed nipples on the calipers and the clutch slave. So I guess the only bleeding process for the ABS pump is to bleed through a caliper. I'm going to be trying that approach with the left front first (appears to be shortest path to the pump).
08-31-2013, 08:11 AM
#50
Burning Brakes
Steve, the brake circuits are effectively independent of the ABS unit, so I doubt that bleeding will accomplish anything. The pump when activated is returning hydraulic fluid to the master cylinder.
When the brake pedal is pressed and the control unit via the wheel speed sensors
detects either the front left, front right or a rear wheel starting to slip the ABS will then
activate. The first mode the solenoid valve or valves adopts is the Pressure Holding
Phase. If the braked wheel reaches the lock limit by way of hydraulic pressure from
the brake master cylinder, further pressure increase in the wheel brake cylinder will
be prevented. The solenoid will receive current of approx. 2 amperes, the solenoid
valve piston is activated and outlet as well as inlet of the solenoid valve are closed.
Hydraulic pressure between hydraulic unit and wheel brake cylinder remains constant
regardless of the pressure being applied to the brake pedal by the driver.
Warning: If and when the ABS activates do not attempt to pump the brake pedal or to
take the foot off the pedal. Once activated the driver must allow the ABS system to
do its work.
If during the pressure holding phase the wheel or wheels continue to move towards a
slip or a skid the control unit will then command the solenoid valve (s) into the
Pressure relieving phase. A current higher than 5 amperes is applied to the electric
solenoid valve which causes a greater piston stroke. The outlet of the solenoid valve
is opened and hydraulic fluid flows to pump reservoir and to the return delivery pump.
Return delivery pump returns the brake fluid into the brake master cylinder against
existing pressure. A damper is provided in each brake circuit to suppress the delivery
noise. The pump always runs during regulation, even if return delivery is not required.
The switching of the solenoid valves between the hold and relieving conditions is
what provides the modulating action of the brake pedal which is felt by the driver.
Once the slip or skid has been successfully dealt with, power is removed from the
solenoid valve(s) and the system returns to the pressure build up phase which allows
full master cylinder pressure to the brake calipers to be resumed.
When the brake pedal is pressed and the control unit via the wheel speed sensors
detects either the front left, front right or a rear wheel starting to slip the ABS will then
activate. The first mode the solenoid valve or valves adopts is the Pressure Holding
Phase. If the braked wheel reaches the lock limit by way of hydraulic pressure from
the brake master cylinder, further pressure increase in the wheel brake cylinder will
be prevented. The solenoid will receive current of approx. 2 amperes, the solenoid
valve piston is activated and outlet as well as inlet of the solenoid valve are closed.
Hydraulic pressure between hydraulic unit and wheel brake cylinder remains constant
regardless of the pressure being applied to the brake pedal by the driver.
Warning: If and when the ABS activates do not attempt to pump the brake pedal or to
take the foot off the pedal. Once activated the driver must allow the ABS system to
do its work.
If during the pressure holding phase the wheel or wheels continue to move towards a
slip or a skid the control unit will then command the solenoid valve (s) into the
Pressure relieving phase. A current higher than 5 amperes is applied to the electric
solenoid valve which causes a greater piston stroke. The outlet of the solenoid valve
is opened and hydraulic fluid flows to pump reservoir and to the return delivery pump.
Return delivery pump returns the brake fluid into the brake master cylinder against
existing pressure. A damper is provided in each brake circuit to suppress the delivery
noise. The pump always runs during regulation, even if return delivery is not required.
The switching of the solenoid valves between the hold and relieving conditions is
what provides the modulating action of the brake pedal which is felt by the driver.
Once the slip or skid has been successfully dealt with, power is removed from the
solenoid valve(s) and the system returns to the pressure build up phase which allows
full master cylinder pressure to the brake calipers to be resumed.
09-01-2013, 11:42 AM
#52
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I took a quick trip yesterday morning to one local Porsche dealer to speak with their service department. I was pleasantly received and had about an hours worth of quality time with the lead technician.
No definitive outcome was reached as two of their newer scanners would not communicate with the ABS controller and their ABS 2 LED tester was incomplete (major bummer as I thought I would have my answer with this tool).
The consensus to this point is that with the ABS unit not setting off an alert until the vehicle actually reaches 5 mph that the ABS unit at start up is acting normally as it runs thru a series of start up tests. Its not until the vehicle moves and the unit runs thru a another series of tests that the unit sets off an alert. The thinking currently is that an input signal or lack of an input signal is triggering the ABS unit to shut down. Which one is the question that the ABS 2 LED tester hopefully will answer. Now, the search is on to find this testing unit. Anyone known where to find this test unit? For sale / rent/ borrow?
I have printed out the wiring diagrams to hopefully gather some insight into what signals feed into the ABS unit.
No definitive outcome was reached as two of their newer scanners would not communicate with the ABS controller and their ABS 2 LED tester was incomplete (major bummer as I thought I would have my answer with this tool).
The consensus to this point is that with the ABS unit not setting off an alert until the vehicle actually reaches 5 mph that the ABS unit at start up is acting normally as it runs thru a series of start up tests. Its not until the vehicle moves and the unit runs thru a another series of tests that the unit sets off an alert. The thinking currently is that an input signal or lack of an input signal is triggering the ABS unit to shut down. Which one is the question that the ABS 2 LED tester hopefully will answer. Now, the search is on to find this testing unit. Anyone known where to find this test unit? For sale / rent/ borrow?
I have printed out the wiring diagrams to hopefully gather some insight into what signals feed into the ABS unit.
09-01-2013, 12:19 PM
#53
Nordschleife Master
Thread Starter
I've spent the best part of the weekend looking at the problem with no success. I've:
Cleaned up all the grounds I could find on the ABS wiring - some were very corroded especially those close to the tranny tunnel.
Did an extensive fluid bleed - no signs of air being expelled
Checked that the ABS pump runs - with 12V applied to pin 9 on the pump unit, it fires up straight away.
Cleaned up the ABS unit plug.
Did test drives with speed sensors unlugged - sure enough I get ABS failure as soon as the car is moving.
Tried the rear sensors (that I removed and replaced with new ones) in place of the front sensors - these have longer cables but the part number stamped on them is identical to the front ones.
Unplugged and replugged the central informer (under the dash)
Next up is to try swapping the ABS controller with another one. I may also consider just buying new front sensors to try but as these are only available from Porsche at the moment, £140 per sensor would be a bitter pill if they didn't solve the problem.
The other thing I noticed is a clicking noise from the right rear wheel. Especially when reversing. On inspection this turned out to be a brake pad moving in the caliper. As I rotate the wheel the brake rotor contacts the pad at a particular point causing it to move. The rotor is relatively new but is clearly not running true which makes me wonder if the wheel bearing is bad which brings me back to Adrian's book which says on p399:
"If wheel bearing fails, wheel will tend to wobble. This affects the gap between the wheel speed sensor and the pulse wheel. This will be detected by the control unit as a sensor failure and will automatically fail the system."
Cleaned up all the grounds I could find on the ABS wiring - some were very corroded especially those close to the tranny tunnel.
Did an extensive fluid bleed - no signs of air being expelled
Checked that the ABS pump runs - with 12V applied to pin 9 on the pump unit, it fires up straight away.
Cleaned up the ABS unit plug.
Did test drives with speed sensors unlugged - sure enough I get ABS failure as soon as the car is moving.
Tried the rear sensors (that I removed and replaced with new ones) in place of the front sensors - these have longer cables but the part number stamped on them is identical to the front ones.
Unplugged and replugged the central informer (under the dash)
Next up is to try swapping the ABS controller with another one. I may also consider just buying new front sensors to try but as these are only available from Porsche at the moment, £140 per sensor would be a bitter pill if they didn't solve the problem.
The other thing I noticed is a clicking noise from the right rear wheel. Especially when reversing. On inspection this turned out to be a brake pad moving in the caliper. As I rotate the wheel the brake rotor contacts the pad at a particular point causing it to move. The rotor is relatively new but is clearly not running true which makes me wonder if the wheel bearing is bad which brings me back to Adrian's book which says on p399:
"If wheel bearing fails, wheel will tend to wobble. This affects the gap between the wheel speed sensor and the pulse wheel. This will be detected by the control unit as a sensor failure and will automatically fail the system."
09-02-2013, 09:24 PM
#54
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Good news on this front. Would you believe the thickness of an "O" ring would be the cause of my ABS fault (.856" to be exact).
The repair seed was planted when the lead technician at the local dealer identified the problem was an "input" signal. The water for the seed was when the service director made a comment about how critical the sensor distance to the timing gear is. After printing out the wiring diagram (24x36, I highly recommend this for ease of following circuits and actually seeing the print) it was obvious the inputs for the ABS were few. Other than a voltage reading from the abs relay, 2 grounds for the solenoid valves, 1 term 31 ground, the wheel sensors were the last inputs.
I was able to take a photo from the backside of the front upright to visually see, I was also able to measure the sensor distances with the sensor removed. Comparing the front sensor gap with the rear I visually noticed a difference.
The "O" ring was staring me in the face, it was the solution to decreasing the sensor gap and move the sensor closer for a stronger input reading. Measurements verified there were no clearance issues with the gear.
Reassembly and a quick road test had me believing I had found the solution. I've taken three separate trips with multiple hammer readings since the repair. Nice results as my rear brakes now actually work with no ABS lights / tones.
Hind sight, I placed the "O" ring there in the first place when I assembled everything. The factory rear trailing arms have a machined groove for it's "O" ring to recess into and I assumed an "O" ring was necessary for the front. The front EVO uprights do not have the recess and the "O" ring raises the sensor height weakening the input reading. Makes sense...no pun intended ;-)
Now on to the A/C codes.
The repair seed was planted when the lead technician at the local dealer identified the problem was an "input" signal. The water for the seed was when the service director made a comment about how critical the sensor distance to the timing gear is. After printing out the wiring diagram (24x36, I highly recommend this for ease of following circuits and actually seeing the print) it was obvious the inputs for the ABS were few. Other than a voltage reading from the abs relay, 2 grounds for the solenoid valves, 1 term 31 ground, the wheel sensors were the last inputs.
I was able to take a photo from the backside of the front upright to visually see, I was also able to measure the sensor distances with the sensor removed. Comparing the front sensor gap with the rear I visually noticed a difference.
The "O" ring was staring me in the face, it was the solution to decreasing the sensor gap and move the sensor closer for a stronger input reading. Measurements verified there were no clearance issues with the gear.
Reassembly and a quick road test had me believing I had found the solution. I've taken three separate trips with multiple hammer readings since the repair. Nice results as my rear brakes now actually work with no ABS lights / tones.
Hind sight, I placed the "O" ring there in the first place when I assembled everything. The factory rear trailing arms have a machined groove for it's "O" ring to recess into and I assumed an "O" ring was necessary for the front. The front EVO uprights do not have the recess and the "O" ring raises the sensor height weakening the input reading. Makes sense...no pun intended ;-)
Now on to the A/C codes.
09-03-2013, 07:01 AM
#55
Nordschleife Master
Thread Starter
Great to hear that you found a result Tom. I don't think the O rings are the problem with mine because all hubs have the recess for the O rings, so front and rear should sit at the correct distances. However I might pull the new Bosch rear sensors and compare the dimensions to the originals.
09-03-2013, 10:39 AM
#56
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I don't recall seeing an official sensor gap in the manual, although I'm sure there is, I just have not found it yet.
I would be curious to know if I need to space this any differently or if a thin gasket of some kind would be warranted for moisture although its currently a greater distance than the rear.
My front spacing with the EVO uprights and a stock metal sensor, 0.037" (sensor base to tip 1.117", base to gear 1.154") , put the "O" ring back in and the gap was .122" (correction from above post "O" ring measured .085" not .856)
The stock rear measured (sensor base to tip 1.118" and the base to gear 1.134") for a sensor gap of .016"
Hope this helps out.
Tom
I would be curious to know if I need to space this any differently or if a thin gasket of some kind would be warranted for moisture although its currently a greater distance than the rear.
My front spacing with the EVO uprights and a stock metal sensor, 0.037" (sensor base to tip 1.117", base to gear 1.154") , put the "O" ring back in and the gap was .122" (correction from above post "O" ring measured .085" not .856)
The stock rear measured (sensor base to tip 1.118" and the base to gear 1.134") for a sensor gap of .016"
Hope this helps out.
Tom
09-03-2013, 12:58 PM
#57
Nordschleife Master
Thread Starter
Thanks Tom for the precise info. Those gaps are small. I'm now wondering if the Bosch sensors I put in were too long (I recall them looking deeper than the originals). Maybe they worked for the one trip I did with no warning lamp before they got chewed up! I'll pull them at the weekend and have a look.
09-03-2013, 02:37 PM
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09-04-2013, 08:00 PM
#59
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Steve,
I have 2 abs sensors for the front spare which i got second hand off ebay when i had my problems with the abs. Did most of the checks you have and turned out to be the relay for me after having a nightmare with sensor bolts shearing off then drilled pilot hold in the bolt ready for an easy out tap to remove the and proceeded to snap the hardened steel easy out in its place. Nightmare.
Anyway turned out to be the abs relay for me after all the work i did. So anyway i have 2 abs sensors in my garage spare and if it helps, i can post them out to you to try mate if that helps.
Tim.
I have 2 abs sensors for the front spare which i got second hand off ebay when i had my problems with the abs. Did most of the checks you have and turned out to be the relay for me after having a nightmare with sensor bolts shearing off then drilled pilot hold in the bolt ready for an easy out tap to remove the and proceeded to snap the hardened steel easy out in its place. Nightmare.
Anyway turned out to be the abs relay for me after all the work i did. So anyway i have 2 abs sensors in my garage spare and if it helps, i can post them out to you to try mate if that helps.
Tim.
09-06-2013, 09:26 AM
#60
Nordschleife Master
Thread Starter
Tim, that would be great. I'll pm you my address to send them to. It would be good to give them a try. 
The plot thickened at the weekend when I travelled down to castle combe for a track day. I'd swapped the ABS controller for another before the trip but the warning came on pretty much every time i moved off after starting the car (so at least a controller fault is now eliminated). I put a piece of tape over the light at one point so that it wasn't in my mind while track driving.
Wierdly, on the trip home in stop start traffic there was a section of the journey when it never came on. The only difference being that it was getting dark and I put my headlights on before moving off!
The plot thickened at the weekend when I travelled down to castle combe for a track day. I'd swapped the ABS controller for another before the trip but the warning came on pretty much every time i moved off after starting the car (so at least a controller fault is now eliminated). I put a piece of tape over the light at one point so that it wasn't in my mind while track driving.
Wierdly, on the trip home in stop start traffic there was a section of the journey when it never came on. The only difference being that it was getting dark and I put my headlights on before moving off!