2012 C4 ABS, ECM, EPB, ESP Issue

[knotty1972]

Hi, after a bit of a steer please and some real wiring diagrams and any data to help my diagnostics. I'm an ex-tech scratching his head ATM.

My Mrs C4 VIN VF7**************[VIN obfuscated, can be read by forum staff] has developed an ABS, ECM, EPB, ESP fault, which I suspect may fall onto the ABS module, but lets see what you can give.

The bit that's nagging at me the most is actually not captured by a DTC. If you do a code clear and drive the car slowly up the street and brake, it feels like the NSF ABS is pulsing, or it feels like there's a crack in the disc (which it hasn't). You slow down and all the time you feel that brake lightly pulsing, but there's never ever a DTC to say there's anything wrong with that wheel. You drive 400 yards and the ABS triggers some DTCs and then the pulsing is gone, as the ABS is off. The ABS sensor resistance etc. all check out.

The actual fault

My Snap-on Solus gets a few codes:

PCM
U1213 - Intersystem CAN: One of the parameters present in the datastream for the ABS/ESP is invalid.

ABS
C1326 - Rear left wheel speed sensor signal fault : Coherence.
C1391 - Non - Acknowledgement of the engine torque fault : Not characterized.
U1219 - Electroincally controlled parking brake (FSE) automatic trigger fault : Data invalid.

Past Weekends
Initially I saw the NSR Wheel sensor code and fitted a new one. No good, as the DTC flagged without the car moving. I measured the resistance of the sensor and then compared it to the OSR and all seems fair. 14 Omhs on the new one and 15 ohms on the other side. I've checked the continuity down to the NSR sensor from the ABS module and spot on too.

Suspecting an internal issue in the ABS module, I found an ABS unit on ebay with the correct part number. I fitted it, but my Snap-On would not communicate with it at all. I wasted a good 1/2 day mesing. I reconnected the original ABS module, and I can communicate fine. I spoke to a friend of a friend who is a Cit/Pug specialist and he said there's no programming needed on the ABS module to stop communication and it should be plug and play, which suggests the eBay ABS module is faulty. I refitted the original ABS module and as I said, it will comm etc.

I've also popped a new EPB switch on, as they are easy, cheap and I've heard they are problematic. Still no changes.

Today
I've had a bit more of a dabble today, using Haynes Pro resource, but I've not found anything standing out and the wiring diagrams aren't great.

Can anyone share any Engine, ABS, BCM wiring diagrams, as I need to go through the loom to double-check the wiring for the CAN DTCs.

Oh, and to top it off, before I packed up today, all of the DTCs cleared without issue as I finished, but 5 minutes before they wouldn't delete, which just makes me more suspect of a wiring issue or a module. I've not taken it for a test drive, as I need to do brake bleed, but not sure it's worth wasting the fluid atm.

Thanks, Phil.

[RichardW]

What does the live data say about the suspect speed sensor? Although you have continuity, it's not impossible that the wire has rotted through and is giving a spiky signal, I would have it out the conduit and check it.

[knotty1972]

Hi, the live data is fine. All sensors reporting the same speed. I’ve just bled the brakes and taken it for a short 1/2 mile spin to check the pedal for air and we have no codes. However, we have the NSF pulsing every time the brake is applied and still nothing relating to it.

[PaulC5]

How can you tell it is just the NSF brake pulsing with the abs - I would have thought if the abs is pulsing it would affect all the brakes ? Have you dismantled that brake to clean the pads/ grease relevant pad backing contact points/made sure any caliper slide pins are clean/checked the disc is not warped using a dial gauge/checked the caliper piston is not seized ?

If you do replace a wheel sensor you might have to run the car for any faults to clear so just swapping and then checking without running may give a false indication a fault has not been fixed.

Many years ago I had the brake pedal pulsing on a Maxi, before abs was used, thought it was a front brake but it turned out a rear brake drum had worn badly and was cured by replacing the drum. From this I learnt an apparent fault on one wheel may be caused elsewhere.

[GiveMeABreak]

Hi, the live data is fine. All sensors reporting the same speed. I’ve just bled the brakes and taken it for a short 1/2 mile spin to check the pedal for air and we have no codes. However, we have the NSF pulsing every time the brake is applied and still nothing relating to it.

You need to be aware that vehicles with ESP as well as ABS have 2 circuits, of which one is bled in the usual manner with the assistance of another person and the ESP circuit then has to be bled with a diagnostic tool which affects the hydraulic block. Doing half the job will lead to problems.

[knotty1972]

Yep, all bled up using Snap-on Solus.

[GiveMeABreak]

I can only suggest it may need doing again or there's an air lock possibly still there.

[knotty1972]

Nope, not even slightly. It was doing it before it was removed.