P38A ABS fault finding Gems 4.6 / Wabco C

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awkwardbob

awkwardbob

Well-Known Member
Posts
578
Location
Glasgow
Hi folks,

I’ve posted before asking about abs sensors and so in but I think I may have a bigger issue with my abs.

I have the fault where the ABS light comes on but doesn’t go off.
Initially this started after I’d had the dash out to replace some blown bulbs but that may be a coincidence.
Nanocom finds the Wabco ABS and there are no faults.
Driving the vehicle, nanocom has an issue registering an input from the speed sensors.
Initially it was just the front 2 which read 0 mph and the rears read road speed, now they all read 0.
The Sensors return about 950 ohms and seemed to be working ok- although they are very well seized.

The fuses seem ok, not sure how to test the relays.
could it be the ECU ?

what might be a sensible way to fault find this ?

or do I need to swallow my pride and pay someone to look at this ?

thanks in advance for any help :)

Bob
 
Do you have an accumulator/pump problem? I had similar and was pump pressure switch. After start up does the pump keep running after 45 seconds? If so there is a problem
 
awkwardbob said:
I will investigate but I don’t think so.

would that flag up as an error in nanocom ?
Click to expand...
Not sure but the great wammers helped me with my problem and he explained the pump should be upto pressure at 45secs and if it carries on running theres a fault with accumulator or pump
 
Mark Piercy said:
On the nanocom, you are using the appropriate wabco program?
What year is your 38'?
Click to expand...
It’s a 97 Gems 4.6 with Wabco C.
I get in via: Range Rover/p38/gems

it can see and interrogate the module, read pressures and switch positions,it used to read road speed for the rears but now they’re all 0.

I wonder if it’s worth swapping the ECU as they seem to only be £10 on fleabay
 
Hmm, yeah I was crawling around 10 mph.

I’ll jack her up and check the resistance to see if it changes as the wheel rotates.

what puzzles me though is:

why did it suddenly fail after replacing dash (or had that bulb blown and I was unaware of the fault) ?
Why did both fronts not register but the rears did ?
Why now do none of them read ?

or... does it make a difference if you’re trying to read kph or mph on nanocom ?
 
Good questions, set the nanocom to read your speed as your clocks do I.e mph or kmh. It may not make a difference.
Have you checked all four for resistance and again with the wheels rotating as well.
 
The Nanocom wheel speed display is fairly useless. Tried it today on my 98 GEMS with Wabco-C. Initially the Nano connected to the ECU but didn't display any data, so I upgraded it to V1.35 and then it connects. All four wheels read 1 MPH while stationary. Then drove down the road and got an "E2" display on the Nano. No further communication possible until switch ignition off & on again. Read faults and apart from an old stored pressure sensor fault which cleared ok, there were no other faults. ABS is working well though !!

I do wonder if the ECU still blocks communications if one or more wheels does not exceed 2kph ?

From the Nanocom Wabco-C PDF on their website:

"It is only possible to communicate with the ABS ECU when the system is in its idle state, that is with the ignition on and the engine running or not. Once the ECU has detected a signal from all sensors that indicates each one has exceeded 2km/h the ECU turns off the dash lamp and exits diagnostic mode. All ECU resources are then used to monitor the sensors and diagnostic communication is no longer possible until the ignition supply has been disconnected and then re-connected."
 
Ok... so a few answers.

nanocom will read in either KPH or MPH

I now have 3/4 sensors reading ok but the 4th (left front) is not registering. (Which may be why it stays in diagnostic mode long enough).

curiously it was RF I was worried about as if brutalised it trying to remove it, I left the LF one alone while changing the brake disc and pads.

Maybe a wee bit of a clean and a technical ‘tap’ might cause it to spring back into life again too.

brakes all seemTo work fine, no errors no pump running on, no TC warnings, etc.

will persevere !
 
I have had 2 aftermarket ABS sensors go "pop" on my MY2000 P38. Both on the OSF.
Last time it went was immediately after hitting a pothole while accelerating quite hard.
Changed the ABS sensor (again) and all ok once more. Mine is a Wabco-D all wheel TC variant.
Strangely, contrary to popular opinion the supply volts across the abs sensors (where they plug into the loom) is 5.3V and not 12V.
 
I seem to recall the headings weren't right in one of the Nanocom files. Also, I think the D screen does allow speed while going along but the C doesn't or only up to 5mph.
 
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