disco 1 300 tdi abs diagnostics headache

currently working on a mates 300 tdi disco 1.
abs hasnt worked for the 11 1/2 months he's had it, mot due.
(abs light never been on)
he had the 40A pump fuse replaced by an auto spark which promptly blew.
he bought a fleabay special ready to swap when we finished the (mountain of) welding work.

so.....

swapped the modulator.(pump)
put a temp 40A breaker in.
investigated lack of abs warning light on ignition switch on. turns out someone has removed lamp and taped hole up from rear of binnacle. replaced with binnacle illumination light as these are easier to get to and not detremental.
still doesent work. checked diagrams for fuses, all ok. checked for voltage to lampholder on binnacle and found to be dodgy connection. dropped other side to earth bypassing abs ecu and got light on. messing about with lampholder turns out to be another bad connection.
now have light on when ignition on.

road tested, light stays on.

removed abs relay, connected blink switch, performed blink test.
got 2-3 (recirc pump does not operate) which is consistent with the original blown fuse.
deleted this from memory nnd got next-
2-6 (brake light switch failure). unable to clear this from memory (treated as active fault.)
confirmed 12v to switch, 12v out of switch when brake pressed.
tested at ecu pin 27 (ground) and 10 (brake light input). 12v present.
tested at ecu pin 27 (ground) and 25 (brake light input). no volts!
spent ages trying to find wire splice HJ4 to test. (rhs of heater motor somewhere)
randomly retested 27 - 25 and got 12v......
check out ok, but still unable to clear from memory.

eventually....swapped ecu from my disco. (which works) perfomed blink test.
got 2-2. (pump continously running). which it isnt.....
unable to reset.
connected his ecu to my disco and blinked.
got 2-6. (brake light switch failure) unable to reset.

road tested both ecu's in problem motor. abs light stays on.
road tested problem motor ecu in my disco. abs light stays on.

3rd mate turns up in disco.....
his ecu in problem motor reads-
2-8 (no voltage to abs solenoid valves)..........
road tested. abs light stays on.

plugged no. 3 mate ecu onto my disco, roadtest, works fine.
blinked, got numerous 2-8's (stored, not active)

never tested-
problem motor ecu in no.3 mates. (due to different obd connector)
my ecu in no.3 mates. (for same reason)

so....what we need to know is....... how can 3 seperate ecu's give different fault codes in 1 motor? (2 of which are known good units. although having stored faults)

points which we still need to address- small amount of air in back brakes following bleeding. (can just turn wheel by hand under reletive braking pressure)

comments / suggestions welcomed.

cheers,

nrgserv said:

currently working on a mates 300 tdi disco 1.
abs hasnt worked for the 11 1/2 months he's had it, mot due.
(abs light never been on)
he had the 40A pump fuse replaced by an auto spark which promptly blew.
he bought a fleabay special ready to swap when we finished the (mountain of) welding work.

so....what we need to know is....... how can 3 seperate ecu's give different fault codes in 1 motor? (2 of which are known good units. although having stored faults)

points which we still need to address- small amount of air in back brakes following bleeding. (can just turn wheel by hand under reletive braking pressure)

comments / suggestions welcomed.

cheers,

Click to expand...

1. One reason why you are getting different results with different ECU's is that they may well have different versions of software in them - a bit like XP, Vista and 7, but Disco related;

2. I assume you know that there is a front bias to the braking system, such that ligh braking will almost ignore the rear brakes with all braking being done on the front axle only. There is a compensating valve for the brakes on the drivers side of the engine bay iirc.

Good luck

Dave

cheers dave

knew about the bias and pressure reg valve.

did wonder about the software!

however we have sorted the problem, of which i will explain when ive got cleaned up and downloaded some phone cam pics.

back soon!

neil

so, with the abs faults-
due to an unexpected breakdown, i had to sort this out on mate 3's disco first.

http://www.landyzone.co.uk/lz/f8/disco-1-rear-axle-radious-arm-bracket-failure-117150.html

while doing so, i left mate 3 reading and deleting abs fault codes on the problem motor. he managed to delete the lot, ending up with a 1-1 blink (system correct, no faults stored)

on road testing, abs light stays on.

re blinked, got front nearside sensor lost signal. (cant remember code as i left manual in workshop)


tested resistance - 925 ohm. (good between 500 - 2000)
checked output volts (ac) - 0.02v. (should be above 0.2v at 30 rpm) - suspect pickup??

clouted sensor to bottom of hole. (gently!)
no difference.

checked same on off side front
927 ohm
2.3v
intention to swap sensors until we found this



brake pipe bracket not bolted correctly holding sensor up if you cant make the picture out.
refitted with both swivel pin bolts to top of bracket.
2.7v from sensor when wheel spun.
abs light goes out on road test!
abs works ok.

mate 3 now deletes all his faults from his ecu while i finish his motor.
all ecu's replaced in their respective motors.

still cant explain while the 3 seperate units gave different faults, but it had been a long day.

still need to bleed air from rear, and lookin at the state of the front brake pipes, then guess its another job before the test.......
and still got bushes to do......

cheers to all and hope this helps someone else.

neil

nrgserv said:

still cant explain while the 3 seperate units gave different faults, but it had been a long day.

Click to expand...

As far as i know about diagnostics i can tell u that an explanation or the continuation of the mistery can be obtained just if the fault code readings are different in the same conditions / same live data. As u can see some of the elements of the diagnosticable systems have a quite wide range of compliance(0-5v; 500-2000ohm;etc).....different inputs could generate different readings taking into account that what u've got wasnt a system failure..........i can't find other explanation

having talked it thru afterwards, the only reasonable conclusion we have come to is
the different faults read in the problem motor with different ecu's, were faults generated from the donor motors. ie stored faults.

as we had an active fault on the problem motor, (that we didnt know about) that only presented its self after road testing, then it became a stored fault.

what i wasnt aware of, is stored faults are read on the blink test numericly, not as they happen. (ie 2-2, 2-5, 2-14 etc)

so the active fault 2-14 when road testing becomes a stored fault when testing, and will be read after 2-13, 1-12 etc.

it was only after mate 3 deleted all the stored faults that the active 2-14 became the only stored fault to recur. we then investigated and found the bracket fouling the sensor.

we would probably have found it with any of the ecu's after deleting the memory.

as an aside, does anyone know if stored faults can be deleted en-mass?
hawkeye, testbook etc?

bit of a headscratcher, what with the taped up lamp hole on the dash. made us wonder what else may have been disconnected / removed to fool mr mot man into thinking it was all ok.

and finally, if you need to know if you have any stored faults, without blinking-

turn your ignition on. abs light comes on, (1 second ish) goes off, (1 second ish) comes back on continously. goes off when road speed exceeds 4 mph.
you have no stored faults

ignition on, abs light comes on and stays on. goes off when road speed exceeds 4 mph.
you have stored faults

ignition on, abs light comes on, stays on, stays on while moving.
you have active fault/s
this should need sorting before the mot. if the testers doing the job right, it should fail!

cheers!
nrg

nrgserv said:

as an aside, does anyone know if stored faults can be deleted en-mass?
hawkeye, testbook etc?

Click to expand...

Yes...i did this with hawkeye(of course for each system separately)

sierrafery said:

Yes...i did this with hawkeye(of course for each system separately)

Click to expand...

rofl! 3 ecu's plugged together!

cheers