Abs Fail (Sensor & Ring Replaced!) - Help Please

[TerryG]

I hope someone can help advise on my problem with ABS.  The ABS warning light displayed - my usual (reliable) garage checked the ECU read out which showed near side front fault - the sensor and ring were replaced but the fail light is still showing and the same fault code is still displayed.  My mechanic seemed reluctant to go further as the diagnostics are still showing the same fault and he said it could be a fault with either wiring, the ABS pump or ECU, all of which would be very expensive.  So we are now driving without ABS which  I am not happy about.  We seem to have no ABS specialists in the area (near Skipton, North Yorkshire) so I am at a loss as to what to do next being very reluctant to just throw money at it when the problem may still not be cured.

 

Any help, guidance, suggestions etc gratefully received, thank you.

[xavier]

Has the sensor has been disconnected and the connecor plug and socket cleaned to eliminate a poor connection? has the sensor been fully seated into the hole in the hub and has the required clearance from the reluctor ring? there's also a possibility the new sensor could be faulty (unlikely though), where was it obtained from (i.e. is it a cheaper or more expensive one).

[TerryG]

Xavier, thanks for the response.  I have to presume that the mechanic that did the work (and has, reasonably reliably for 10 years) did a proper job.  Assuming that, what next?

[sparky Paul]

xavier's points are all valid, the most likely suspects must be eliminated first. The mechanic is unlikely to have tried a second replacement sensor, and though unlikely, you do get the odd dud. Was it a genuine or pattern part?

 

I would most definitely check the airgap, the distance is critical. When the sensor is replaced, the rust scale must be removed from the hub or the new sensor will not fully seat. The sensor can look as though it is fitted correctly from above.

 

If that is okay, the wiring needs to be tested for continuity back to the ABS module. A visual check of the wiring is also worthwhile, particularly around the wheelarch connector.

 

The Teves ABS module can develop faulty sensor inputs. To identify this problem, you can connect an oscilloscope to each of the inputs to confirm the presence and quality of the sensor pulses, with the car raised and wheels turning.

 

Alternatively, a more rough and ready approach is to chop the wiring at the ABS module connector and switch the two front sensors. If the fault code transfers to the other side, it's the sensor or associated wiring. If the fault stays on the same side, it's the ABS module. Don't forget to return the wiring to it's original state, or the ABS will not work correctly once the fault is rectified. Trace the wiring back from the wheelarches, or use the wiring diagrams from TIS to identify.

 

 

What was the exact fault code? This may help identify whether wiring, sensor or module is at fault.

[TerryG]

Thanks Paul

 

I will risk asking my mechanic to check these things and hope not to offend him! 

 

Sorry to be ignorant - what is the Teves module, is it the ABS ecu; if so, where is it and how much would one expect to pay for a replacement unit?

 

I don't know what the exact fault code is but I will try to find out.

[sparky Paul]

The exact fault code might help you determine where the fault lies, so it is very important.

 

You should be able ask your mechanic to double check the sensor gap without offending him, just tell him you have been told it is a common problem when replacing sensors on these cars.

 

 

Teves is the make of the ABS system, the ECU module is generally reliable but sensor input failure is not unknown.

 

Rather than fitting a secondhand unit, personally I would probably send the unit to somebody like BBA-Reman for repair.