ABS fault with no fault codes

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As data says I’ve you getting a message on dash could be becm related sorry to hop on your post I wasn’t getting message on dash about abs just traction control but have removed earth under the fuse box to clean it up and now getting abs fault message and the dreaded light will check when its clean and back on and report back
 
As expected, new brake switch fitted and no difference unfortunately. Been for a drive and it's just the same as before.

Anyone got any ideas what to check next? I'm considering changing the 4 ABS sensors themselves in case one of them has an intermittent fault which throws the light on the dash.
 
domlinson said:
As expected, new brake switch fitted and no difference unfortunately. Been for a drive and it's just the same as before.

Anyone got any ideas what to check next? I'm considering changing the 4 ABS sensors themselves in case one of them has an intermittent fault which throws the light on the dash.
Click to expand...
You'd definitely get a fault code if the sensor was dead/unplugged
 
kermit_rr said:
You'd definitely get a fault code if the sensor was dead/unplugged
Click to expand...
As Kermit says, a duff sensor will generate a fault code.
Does the ABS actually work is you brake on loose gravel for example? If you try it and the ABS does kick in, you can be sure that the fault is not in the ABS ECU.
I still think it's likely to be a phantom fault from the BECM.
 
Datatek said:
As Kermit says, a duff sensor will generate a fault code.
Does the ABS actually work is you brake on loose gravel for example? If you try it and the ABS does kick in, you can be sure that the fault is not in the ABS ECU.
I still think it's likely to be a phantom fault from the BECM.
Click to expand...

I will go and give that a try later today, great idea. I'm happy to drive it because the brakes work absolutely fine, but haven't tried to get ABS to kick in yet.

Just to confirm, i've triggered ABS plenty of times before (I used to test drive vehicles at Millbrook proving ground, not on the public roads haha), does the P38s ABS work in the same way? So if ABS is working, I should feel feedback in the pedal?
 
domlinson said:
As expected, new brake switch fitted and no difference unfortunately. Been for a drive and it's just the same as before.

Anyone got any ideas what to check next? I'm considering changing the 4 ABS sensors themselves in case one of them has an intermittent fault which throws the light on the dash.
Click to expand...
Sorry to hear its still broke Dom' .... Did you take a look at the ABS High/Low pressure switches and/or replace it already?
The ECU tells the BECM to light the light.
There are no fault stored in the ECU and all the Sensors looked good.
"IF" (I only say if) there is a hard fault where the ABS unit is reporting incorrect pressures to the ECU because the switches are duff/have failed then any new/Spare ECU will see exactly the same thing and the fault is still there.
You are unlikely to get it through an MOT in this state I fear.
I wonder if you could jumper out the switches to report different pressures and see if the fault magically disappears? ;)

I don't have a fault and I could stick my Nanocom on and see what it says the status is of the pressure switches. The manual says you can get at them with Nanocom.
upload_2022-10-13_16-56-16.png



upload_2022-10-13_16-45-1.png
 
Last edited:
Just tried.. ignition on.. abs light and no message, as normal.
Ignition off, unplug sensor, ignition on. Abs fault, TC light on and traction failure message. Ignition off, plug back in and no abs fault message but still got the traction failure message.

Nano has decided not to work, so unable to check/clear any faults :D
 
DanClarke said:
Sorry to hear its still broke Dom' .... Did you take a look at the ABS High/Low pressure switches and/or replace it already?
The ECU tells the BECM to light the light.
There are no fault stored in the ECU and all the Sensors looked good.
"IF" (I only say if) there is a hard fault where the ABS unit is reporting incorrect pressures to the ECU because the switches are duff/have failed then any new/Spare ECU will see exactly the same thing and the fault is still there.
You are unlikely to get it through an MOT in this state I fear.
I wonder if you could jumper out the switches to report different pressures and see if the fault magically disappears? ;)
View attachment 275989
Click to expand...

Thanks @DanClarke - Good idea, that will help me debug the issue. Is this diagram from Rave?

kermit_rr said:
Just tried.. ignition on.. abs light and no message, as normal.
Ignition off, unplug sensor, ignition on. Abs fault, TC light on and traction failure message. Ignition off, plug back in and no abs fault message but still got the traction failure message.

Nano has decided not to work, so unable to check/clear any faults :D
Click to expand...

Thanks for trying that @kermit_rr, that confirms that my specific issue is most likely not sensor related as I don't get the TC light or traction failure messages.
Sorry that your traction failure message remains! I wonder if the ECU needs to see movement in all sensors again to clear it?
 
DanClarke said:
Yes it is. I have updated my post further to suggest I take a look at the status of my own pressure switches with my Nanocom for comparison purposes.
Click to expand...

Just had another look in Rave at the warning lamp functionality, attached below...

According to this, what I am seeing (ABS warning lamp stays on, ETC lamp off, Brake warning lamp off) means: "ABS fault condition detected by ECU".

In addition, I think your pressure theory might be out the window @DanClarke - a combination of the three lights is used to show the pressure states in the system so I think that if I had a pressure issue, I'd be seeing the ETC and red Brake light too?

Screenshot_20221013-170530_Drive.jpg
 
@domlinson
I just found this on another forum (wash my mouth out).

OK, the Workshop Manual says :
The ABS power unit consists of an electrically driven pump, a pressure switch and an accumulator.
The pressure switch incorporates three electro-mechanical switches: one for the pump, another, at a different pressure setting, to illuminate the pressure warning lamp. The latter switch plus a third switch inform the ECU of low pressure and that ABS function should cease while pressure remains low.
The pump also incorporates a non-return valve and a pressure relief valve to protect the system.
NOTE: The pump and pressure switch are not serviceable, if failure occurs a new unit must be fitted.
 
domlinson said:
Just had another look in Rave at the warning lamp functionality, attached below...

According to this, what I am seeing (ABS warning lamp stays on, ETC lamp off, Brake warning lamp off) means: "ABS fault condition detected by ECU".

In addition, I think your pressure theory might be out the window @DanClarke - a combination of the three lights is used to show the pressure states in the system so I think that if I had a pressure issue, I'd be seeing the ETC and red Brake light too?

View attachment 275991
Click to expand...
Fair enough. :)
 
kermit_rr said:
Do the brakes work? Ie do they stop the car.. pump only come on every 4 pedal presses, abs and tc work as normal?
Click to expand...

Brakes feel fine, no excessive pedal travel. Pump only comes on after pressing 4-5 times.

Traction control and ABS are untested as of yet... I need to find some loose gravel to perform safe tests.
 
Hi all,

I think I mentioned somewhere in a previous post that sometimes the ABS Fault pops up and beeps sporadically while driving, not related to the brake pedal being touched... Other times, the ABS Fault pops up once when the ignition is turned on and then never beeps again, even on long drives.

I've made a correlation between the weather and the 2 different behaviours above.
I've subsequently found out that i've got water ingress from the passenger side pollen filter into the cabin, which is where the ABS ECU and wiring is situated.

I've already checked all of the ABS connector pins, and the ECU pins itself and they are all clean. And i've swapped a tested working ECU in, with no change.

Are there any connectors in the passenger footwell that could be ABS related that I'm missing? Apparently the white connectors in the passenger A pillar are EAS only and not related to ABS.

Thanks
 
domlinson said:
Hi all,

I think I mentioned somewhere in a previous post that sometimes the ABS Fault pops up and beeps sporadically while driving, not related to the brake pedal being touched... Other times, the ABS Fault pops up once when the ignition is turned on and then never beeps again, even on long drives.

I've made a correlation between the weather and the 2 different behaviours above.
I've subsequently found out that i've got water ingress from the passenger side pollen filter into the cabin, which is where the ABS ECU and wiring is situated.

I've already checked all of the ABS connector pins, and the ECU pins itself and they are all clean. And i've swapped a tested working ECU in, with no change.

Are there any connectors in the passenger footwell that could be ABS related that I'm missing? Apparently the white connectors in the passenger A pillar are EAS only and not related to ABS.

Thanks
Click to expand...
It's also where all the connections from the various ecu's are presented to the non-OBD2 port, and that same pollen filter saturates the ODB2 port. Maybe that's causing a short there?
 
Still no progress on this annoyingly.

I've had a look at the body ground points in the engine bay (one under the fusebox/coolant reservoir, and the other on the opposite wing near the EAS unit)... both of these are fairly rusty and I believe the ABS system is grounded through these points.

I think I'll clean these up with some sandpaper just as cheap insurance.

Does anyone have any tips for doing this? I don't really like disconnecting the battery on my P38 as I end up needing to put the EKA code in which I feel is asking for trouble... Is it OK to disconnect and clean these ground points whilst the battery is installed? That also sounds like it's asking for trouble... not sure which is worse haha.

Thanks again
 
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