Hi all, my 2002 p38 4.0 is currently plagued by the 3 amigos on the dash and I'm trying to get a new mot on it (the first one in my ownership) but the tester has said he can't give a pass with the lights on and "ABS FAULT" on the dashboard. This is what i know - the braking is good, the pedal is firm, the pump seems to build pressure ok, the abs actually works and all 4 speed sensors work on each wheel. Its had a brand new abs pump switch and accumulator replaced and the braking system has been fully flushed and replaced as per the handbook. The scanner (hawkeye total) I have says "pressure switch 1 - low pressure" while pressure switch 2 is OK. What is pressure switch 1 and should I just replace the pump with a known good one? Any help would be appreciated. Thanks
Datatek
Well-Known Member
The pressure switch is on the pump assembly, it contains 3 contacts, sounds like one has failed. New switches can be found, SAAB, Jaguar and others used the same system but it may take some searching. Otherwise second hand from a breaker. Make sure the connector is not corroded first though.
brianp38dse
Well-Known Member
Have a check of your brake peddle switch as well it needs to be set as per Rave, as if that is wrong it can throw up abs fault.
Montyjohn
Well-Known Member
Strange you're getting this fault with a new pressure switch fitted.
The pressure switch measures for pressure being two low and too high (1 and 2).
Sounds like the too high one is working fine, but it always thinks it has too little pressure.
Are you finding then that the pump kicks in after one use?
After one use, the pressure can't be too high anymore, and if it thinks the pressure is always low, I would expect the pump to come on straight away after using the brakes.
Since the switch is new, I would be checking wring connections.
The pressure switch measures for pressure being two low and too high (1 and 2).
Sounds like the too high one is working fine, but it always thinks it has too little pressure.
Are you finding then that the pump kicks in after one use?
After one use, the pressure can't be too high anymore, and if it thinks the pressure is always low, I would expect the pump to come on straight away after using the brakes.
Since the switch is new, I would be checking wring connections.
Ah so Pressure switch 1 and pressure switch 2 are two switches within the one unit (the green one screwing into the abs pump). If so that does imply either wiring, connector or a pump issue. I'll check out how often the pump kicks in with use and let you know. I'll also have a look at the brake pedal switch.
Ive had the car 4 years, swapped out a duff engine and have only done about 150 legal miles on it all that time! Just need that mot...
Ive had the car 4 years, swapped out a duff engine and have only done about 150 legal miles on it all that time! Just need that mot...
Datatek
Well-Known Member
There are 3 contacts in the brake pressure switch fitted to the ABS pump.
The pump should run about every 4th press of the brake pedal. If the pump cycles then most of the switch is working so check the connector for corrosion and local earth points.
Datatek
Well-Known Member
Switch contacts within the switch assembly which operate at different pressures ascending or descending.
Gotcha
So a bit of follow up. I've checked the wiring at the switch, the abs ecu as well as the plugs by the a-pillars on both sides and they seem fine, cleaned with contact cleaner, checked pins, did continuity testing etc. The only thing I noticed was that the brake fluid sensor was faulty. Beforehand, on ignition and when running the one pressure switch readout read "low pressure" whilst the other read "pressure ok". Now, when I short the wire to the brake fluid sensor, they both read "pressure ok" on ignition but when I start the car, the same switch reads "low pressure" again. I also checked the brake switch and it seems fine and it registers on the hawkeye when you press and depress.
The only possible thing is that the pump would sometimes run every 2 or 3 times the brake was pressed. I'm kinda out of ideas now other than possibly replacing the connectors by the kick panel with soldered connections.
Before I give up completely, what logically is left to do? Replace the abs ecu? Replace the brake pump? I am stumped!
The only possible thing is that the pump would sometimes run every 2 or 3 times the brake was pressed. I'm kinda out of ideas now other than possibly replacing the connectors by the kick panel with soldered connections.
Before I give up completely, what logically is left to do? Replace the abs ecu? Replace the brake pump? I am stumped!
Yeah, agreed. By shorting the fluid level connector with a paper clip, I can get it to read pressure ok on ignition but it just doesn't seem to stay that way once the car starts.
The ABS, TC, and Brake light (now the Airbag light too which is a recent development) are all on regardless of speed - nipped it along the road up to 30mph but no difference. I used the hawkeye's actuator function and each one of the lights will cycle off and on.
I suppose what it comes down to is where does the car get the low pressure signal from?
ABS ECU, I would imagine. That sits up behind the glovebox where water from leaking pollen-filters or windscreen trim drips on it.
Slight update - I've since replaced the ABS ECU too with a known good one but no change either. Given I've changed the accumulator (new), pressure switch (new), ECU, reset brake plunger, short circuited the brake fluid level sensor connection, soldered the connections at A-pillar, and bled the system per Rave, the only part left to do is replace the actual brake pump itself. As I've replaced the bits listed already, is it even possible for a low pressure signal to come from the brake pump if its duff?
Any help would be MASSIVELY appreciated!
Any help would be MASSIVELY appreciated!
If you could, with the engine not running. Press the brake pedal until your sure all the pressure has gone. Then turn on the ignition and measure the amount if time the pump takes to build pressure and switch off. Then one of us could do the same on another 38' and compare results. If the pump is worn logically it'll take take longer to pressurize. 
I believe if the pump takes longer than 43 seconds to pressurize its duff. Longer than 25 seconds and its becoming suspectIf you could, with the engine not running. Press the brake pedal until your sure all the pressure has gone. Then turn on the ignition and measure the amount if time the pump takes to build pressure and switch off. Then one of us could do the same on another 38' and compare results. If the pump is worn logically it'll take take longer to pressurize.
https://uk.rs-online.com/web/p/pressure-gauges/1365200 Will need suitable hose & adapter. Then follow RAVE pump test procedure ?
If you could, with the engine not running. Press the brake pedal until your sure all the pressure has gone. Then turn on the ignition and measure the amount if time the pump takes to build pressure and switch off. Then one of us could do the same on another 38' and compare results. If the pump is worn logically it'll take take longer to pressurize.
I've just done the test and it's taken 35 seconds to re-pressurise so it certainly looks like it's in the suspect zone. At least that gives me a reason to believe I should replace the pump itself now. I didnt know there was a rave procedure to check the pump against so i'll check that out too. I'll see if I can get a new unit sourced and fit in the next week and I'll let you all know.
