A Cautionary Tale....ABS Problems

For over six months I have has ABS problems. I have posted various issues at various times. I bought Faultmate and the ABS software...no ID of problem.
I began with the obvious replace the accumulator and relays : no change.
After days/weeks of elimination I decided that my presssure switch was defective. Through LZ I tracked down a replacement pressure switch and fitted it.....no change.
I was now spending hours daily/weekly on Rave trying to find a switching/wiring problem.
I rigged up a temporary earthing switch which enabled me to run the ABS manually. At leat I knew that the pump actually functions so it must be a wiring problem.
I continued with my search for the answer.
A fault in the fusebox was next diagnosis : new fusebox : strip down...fit...no change.
ECU is only remaining area for examination : tracked down a 2nd hand ECU : I'd hate to buy a new ECU and find no change because it was all down to a broken wire somewhere in the system so before buying I tracked down ( Rave)the whole wiring from battery to ECU including the 30 + connections to the ECU connector.
4 pages of A4 notes on the wiring : analysis of known positives were still pointing to the pressure switch.....SO, I had now ALSO bought a full pump from a delapidated scrapper. Decided to stick in the pressure switch from that on the basis that the chances of THREE switches with the same problem was odds in my favour.
Stuck it in...........YIPPEEYAHOO....whole system works.

The " reconditioned " pressure switch which I had ORIGINALLY bought was also crap.
I was misguided for months because I assumed that the "reconditioned " pressure switch was kosher.
THE MORAL OF THIS TALE IS (1) DO NOT ACCEPT THAT"RECONDITIONED" PARTS ARE ACTUALLY WORKING.(2) if anybody needs advice on their ABS...I think I have visited every corner of the system. Happy to save people from my six months of pain.

million dollar Q....
Do you know what was the difference betwen the good and bad pressure switches?
Is there a diagnostic test to determine whether a switch is good or bad?

The Mad Hat Man said:

million dollar Q....
Do you know what was the difference betwen the good and bad pressure switches?
Is there a diagnostic test to determine whether a switch is good or bad?

Click to expand...

So far as I can make out 1. you can't test it until you can put it under pressure (which is what closes the relays to create the earth) and 2. You can't put it under pressure if it doesn't work !
Diagnostics don't show it as a fault because it's not malfunctioning : it's just not there.
Somebody might know some means of testing it but that's beyond me.
It's the pressure from the abs pump which triggers the diaghram which closes the relay inside the pressure switch.....and it's the pressure switch which fires the abs pump !
I had assumed it was OK because it was "reconditioned" and after months my analysis of the known positives kept pointing to the switch. That's why in desperation I stuck in a third switch from a scrapper.

The Mad Hat Man said:

million dollar Q....
Do you know what was the difference betwen the good and bad pressure switches?
Is there a diagnostic test to determine whether a switch is good or bad?

Click to expand...

It just occurs to me that there is a test and it's the one that I did originally but got misdirected by the duff replacement.
Take a length of wire and earth it to the bolt holding down the batter clamp : bare the other end : remove the rubber sleeve from the connector to the pressure pump : jam the other end of the earth wire into the BLACK AND YELLOW wire in the pressure switch connector while it's in place : switch on ignition. If you're pump fires up the problem is DEFINITELY in the pressure switch.
there are five wires going into the connector : BY goes back to the relay : BG goes back to the fusebox and is the + for the relay insode the pressure switch : BW goes back to the ECU and doesn't appear to go through the fusebox. The other two are blacks and go to a common eart
When I got the pump running by earthing BY it made me think ( not unreasonably) that the problem was a bad earth somewhere in the system. That resulted in futile weeks of tracking down and checking every earth.
I wrongly thought that earthing BY triggered the abs relay (17) : BY goes through the fusebox and is in fact power going to the pressure switch which is earthed by the relay inside the pressure switch being closed by the pressure from the pump.
IF YOU EARTH THE BLAck/YELLOW WIRE AND YOUR PUMP RUNS THE PROBLEM IS DEFIBITELY IN THE PRESSURE SWITH OR THE CONNECTOR. The connector wires are easily checked.
I suspect that an awful lot of perfectly functional ABS pumps have been replaced due to a faulty pressure switch. I have now had two out of three pressure switches faulty ( viz my original which went : the replacement which I assumed was OK and thirdly the scrapper which I put in as a last resort.
You can also replace the pressure switch in situ by using a jubilee clip round it , tapping, slackening, tightening, tapping. Very6 little brake fluid comes out because the chamber that the pressure switch is going into is sealed by a diaghram which activates the plunger on the top of the pressure switch.
There's a million more things I could tell you that I got wrong before arriving here ! DON'T SCRAP YOUR ABS PUMP UNTIL YOU HAVE EARTHED B/Y TO FIND OUT IF THE ACTUAL PUMP PART FUNCTIONS

Nothing to do with abs, but I purchased as new rf receiver from the main stealers and was duff. So the moral of the story is it may be duff, new, old or recon accross the board. Its just a bummer we dont have a draw full of everything to test it out. Well done in your persistance and bummer on the lost time spent digging deep

Very good reply Tak - that reply alone should be in the FAQ section as a "how to". Feedback and that sort of knowledge is what makes this forum great.
How about a "range rover ABS pressure switch test - how to"???

The Mad Hat Man said:

Very good reply Tak - that reply alone should be in the FAQ section as a "how to". Feedback and that sort of knowledge is what makes this forum great.
How about a "range rover ABS pressure switch test - how to"???

Click to expand...

Thanks"Mr. Man"
Do I just copy it and post it there ?
I might know how to fix the abs but I'm hopeless at doing stuff on this very helpful forum.
I could also post pics with it....if I knew how to.... because I now have a spare complete setup on the bench which I used as my test bed.
I've tried to keep the post to the basics but there are also a number of side issues about other red herrings I had to pursue.
If anybody is having this kind of problem I'll be delighted to help because it's a complete pain in the ass, can be expensive and in the final analysis can result in a scrapper/MOT failure.

The Mad Hat Man said:

Very good reply Tak - that reply alone should be in the FAQ section as a "how to". Feedback and that sort of knowledge is what makes this forum great.
How about a "range rover ABS pressure switch test - how to"???

Click to expand...

I've posted in the FAQ'a Section.
It occurs to me that now that I have two duff pressure switches which are no use to man nor beast I should open one of them up to find how they work and what goes wrong.
Problem is that the leccy bits are crimped into the body of the switch : I assume that the only way in is to go round it carefully undoing crimps ?
Any of you engineering types who can offer any advice ?

What were the symptoms of the original problem?

F.

Felix said:

What were the symptoms of the original problem?

F.

Click to expand...

Symptoms were :1 ABS and Brake warning lights remained illuminated 2. No power assisted braking.

I get ABS, Brake warning and TC light on when I start up. Even with hand brake off. They go out after about a minute if if I haven't moved (ABS after movement as normal but stays on until the others go out if moving). Am I about to get something similar?

F.

Felix said:

I get ABS, Brake warning and TC light on when I start up. Even with hand brake off. They go out after about a minute if if I haven't moved (ABS after movement as normal but stays on until the others go out if moving). Am I about to get something similar?

F.

Click to expand...

Frankly I don't know Felix. It might just be that your accumulator is tiring : that's a relatively cheap and dead easy fix.( 5 min job): your pump is obviously running which is pressurising the accumulator. What's your mileage and any idea when your accumulator was last changed ?
I've now posted pics on FAQ's section.

The Mad Hat Man said:

million dollar Q....
Do you know what was the difference betwen the good and bad pressure switches?
Is there a diagnostic test to determine whether a switch is good or bad?

Click to expand...

Thanks for your comments : I have now edited and added pics under FAQ's : marks out of ten ?....even if just for effort !