ABS Control Unit Question
03-27-2010, 09:16 AM
#1
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ABS Control Unit Question
My 1990 C-4 has started throwing the ABS and Interlock (PDAS) lights immediately upon start. I am running through the list of usual suspects for failed components, which led me to removal of the ABS control unit, which was very moist and showed considerable corrosion. After cleaning the connectors and drying-out the unit, I realized that one of the connector pins in the control unit is missing (perhaps corroded completely away?!). Should all of the pins be present? Thanks in advance for any help you can provide.
03-27-2010, 10:04 AM
#2
Three Wheelin'
There are several pins that are not used so you may be lucky!! Diagram attached.
If the ABS/PDAS lights don't go out (they SHOULD come on when the ignition is turned on) it's likely related to a problem with the hydraulic pressure. Take a note if you can hear the electric pump running and when/if it stops. In a perfect world I would expect the pump to stop after, say, 20-30 seconds. More than that suggests the primary hydraulic system needs bleeding. Any more than 2 minutes and you have a more sever problem and should switch off quickly. The pump gets very hot if running for that length of time and will likely damage something else.
Regards
Dave
If the ABS/PDAS lights don't go out (they SHOULD come on when the ignition is turned on) it's likely related to a problem with the hydraulic pressure. Take a note if you can hear the electric pump running and when/if it stops. In a perfect world I would expect the pump to stop after, say, 20-30 seconds. More than that suggests the primary hydraulic system needs bleeding. Any more than 2 minutes and you have a more sever problem and should switch off quickly. The pump gets very hot if running for that length of time and will likely damage something else.
Regards
Dave
Last edited by Computamedic; 03-27-2010 at 11:05 AM.
03-27-2010, 02:49 PM
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Just been in bits.
Hi Dave,
I think you'll remember me moaning about these bloody lights over the last couple of weeks.
Today on the sunny wirral,the weather was on my side so I got involved again trying to get the lights off,I cleaned and checked everything and they are still there.
Sten,borrowed me relays to check on the abs and the lights still light up.
But my pump is cranking for a good 1minute on start up.
So Monday she's getting bled,I have booked her in with Loe bank which is a mate of my mechanic, so he comes highly recommended for fault finding.
This started as a intermitten fault last year and became worse after laying the car up over the bad weather.
If by being laid up I have lost hydraulic pressure what can cause that, the last switch from Porsche on the pump was faulty,I'm putting a new one in before she's on the pressure tester/bleeder.
Lets hope this sorts it, as I love the old girl but warning lights do my head in.
Gaz,
I think you'll remember me moaning about these bloody lights over the last couple of weeks.
Today on the sunny wirral,the weather was on my side so I got involved again trying to get the lights off,I cleaned and checked everything and they are still there.
Sten,borrowed me relays to check on the abs and the lights still light up.
But my pump is cranking for a good 1minute on start up.
So Monday she's getting bled,I have booked her in with Loe bank which is a mate of my mechanic, so he comes highly recommended for fault finding.
This started as a intermitten fault last year and became worse after laying the car up over the bad weather.
If by being laid up I have lost hydraulic pressure what can cause that, the last switch from Porsche on the pump was faulty,I'm putting a new one in before she's on the pressure tester/bleeder.
Lets hope this sorts it, as I love the old girl but warning lights do my head in.
Gaz,
03-27-2010, 06:09 PM
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If the diagram that Computamedic posted is for the control unit pins (and not the connector), then I am completely missing the #9 pin, which is the ground for the acceleration sensors. Does anyone know whether it is possible to remove the unused pins from the control unit and use them in another position? I hate to consider how much a new control unit would cost.
For context, my ABS and PDAS lights appear with the alarm chime as soon as the engine is started and do not disappear. My brake pump runs no longer than usual (maybe 10-15 seconds on a cold start, less or not at all on a warm start) and the brake pressure lamp disappears in the usual amount of time. Driveability remains normal, albeit without ABS and traction control.
When I have had similar symptoms in the past, the lights and chime would occur 20-30 seconds after startup and once the car was underway. I always solved those issues by cleaning the longitudinal accelerometer. With the present problem, I have attempted to clean both accelerometers four or five times without success. The various discussion threads on ABS and PDAS lights led me to check the ABS control unit, and the amount of green / brown rusty corrosion and moisture I found after removing the connector from the control unit was certainly troubling. I cleaned the unit and the connector with a wire brush and electrical contact cleaner and dried both thoroughly with a compressor, but the lights still illuminate, and I am becoming convinced that much of the corrosion was the #9 pin corroding into oblivion.
For context, my ABS and PDAS lights appear with the alarm chime as soon as the engine is started and do not disappear. My brake pump runs no longer than usual (maybe 10-15 seconds on a cold start, less or not at all on a warm start) and the brake pressure lamp disappears in the usual amount of time. Driveability remains normal, albeit without ABS and traction control.
When I have had similar symptoms in the past, the lights and chime would occur 20-30 seconds after startup and once the car was underway. I always solved those issues by cleaning the longitudinal accelerometer. With the present problem, I have attempted to clean both accelerometers four or five times without success. The various discussion threads on ABS and PDAS lights led me to check the ABS control unit, and the amount of green / brown rusty corrosion and moisture I found after removing the connector from the control unit was certainly troubling. I cleaned the unit and the connector with a wire brush and electrical contact cleaner and dried both thoroughly with a compressor, but the lights still illuminate, and I am becoming convinced that much of the corrosion was the #9 pin corroding into oblivion.
03-29-2010, 10:59 AM
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Does anyone know whether the above C-4 diagram depicts the pins on the control unit or the inputs for the pin on the harness connector? I cannot tell whether I am missing the #9 pin (ground for the acceleration sensors) or the #11 pin (voltage, term. 30 - what does this mean?).
Anyone have a used ABS control unit for sale? Alternatively, is there a C-4 owner in the Richmond / Williamsburg / Newport News, VA area who would be willing to let me swap their control unit into my car for a quick test? It's not invasive - the entire unit comes out of the car by removing two nuts.
Anyone have a used ABS control unit for sale? Alternatively, is there a C-4 owner in the Richmond / Williamsburg / Newport News, VA area who would be willing to let me swap their control unit into my car for a quick test? It's not invasive - the entire unit comes out of the car by removing two nuts.
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03-29-2010, 12:11 PM
#8
Three Wheelin'
You should be able to tell whether it's plug or socket by comparing the orientation of the pins. On the diagram, the left side has 19 pins with pin 1 at the end where the cable enters. The middle and right rows only have 18 pins.
Dave
Dave
