Random ABS warning.

Ken Long

Ken Long

Member
On our trip to Scotland last week we had the ABS warning go off. We were driving in fairly unpleasant conditions at the time. The photo below was taken at Sandbach services, it was probably only 15 minutes after setting off again that the warning sounded.

A2 at Sandbach 2.jpg


After pulling off the M6, switching the engine off and restarting the warning had cleared. The weather improved as we headed north but the warning went off again as we approached Carlisle, having passed the turning for @timmus ironically! Again a stop/start reset it. We pressed on and the warning made no reappearance until we within 500m of our accommodation in Laggan. My brother in law had also had ABS warnings on his 21 plate A class Merc so we wondered if the weather early in the journey had caused an issue with the ABS sensors.

We used the car all week, probably doing about 500 miles with no reoccurence of the issue. On our journey home yesterday, it suddenly came on, just as we were approaching our lunch stop. On setting out again, we completed the rest of the trip (maybe 220 miles) with no issue.

On occasion during the week I had to pull up sharply on less than perfect surfaces and the ABS seemed to work fine. The brakes pulled up evenly and the car at no point felt unstable. Is it likely that the snow/ice has affected the ABS sensor? Where is the ABS sensor mounted? Is it front or rear? I ask because the day before we set out the rear shocks and springs were replaced and I wonder if something was disturbed during that process?

Any insight very gratefully received.
 
the ABS sensors are in all four bearing housings. If you are able to see the front bearing housing, the sensor is screwed into the top of the casting so that the end of the sensor is located adjacent to the magnet ring on the bearing itself. Then the wire for this runs up the suspension strut and into the loom - I wonder if you've maybe got slight damage to the wire on one of the corners that was transiently causing the ABS system to get unhappy because of a short to earth or similar owing to the amount of water and slush in the driving conditions? On the rear I think the sensor wire goes into the back of the drum backplate adjacent to where the brake pipe is joined to the rear of the brake cylinder.

control unit for abs; speed sensor Audi A2 (A2) 2003 year Audi EUROPA 927000

control unit for abs<br/>speed sensor Audi A2 (A2) 2003 year Audi EUROPA 927000 spare parts
audi.7zap.com audi.7zap.com

the location where the ABS sensor screws into the front casting can be seen on the left hand bearing housing in my image below :

 
I wonder if a VCDS scan would reveal which wheel sensor / wiring was the issue - if it’s that. Anyone know?
 
Ken Long said:
On our trip to Scotland last week we had the ABS warning go off. We were driving in fairly unpleasant conditions at the time. The photo below was taken at Sandbach services, it was probably only 15 minutes after setting off again that the warning sounded.

View attachment 105845

After pulling off the M6, switching the engine off and restarting the warning had cleared. The weather improved as we headed north but the warning went off again as we approached Carlisle, having passed the turning for @timmus ironically! Again a stop/start reset it. We pressed on and the warning made no reappearance until we within 500m of our accommodation in Laggan. My brother in law had also had ABS warnings on his 21 plate A class Merc so we wondered if the weather early in the journey had caused an issue with the ABS sensors.

We used the car all week, probably doing about 500 miles with no reoccurence of the issue. On our journey home yesterday, it suddenly came on, just as we were approaching our lunch stop. On setting out again, we completed the rest of the trip (maybe 220 miles) with no issue.

On occasion during the week I had to pull up sharply on less than perfect surfaces and the ABS seemed to work fine. The brakes pulled up evenly and the car at no point felt unstable. Is it likely that the snow/ice has affected the ABS sensor? Where is the ABS sensor mounted? Is it front or rear? I ask because the day before we set out the rear shocks and springs were replaced and I wonder if something was disturbed during that process?

Any insight very gratefully received.
Click to expand...
As others have stated it may be that you have an intermittent wiring related fault, but looking at the conditions it’s just as likely that damp in one or more sensor connectors or indeed slush getting in there could have caused these sort of issues. Will be worth a scan just to see what was reported as a first step
 
I've had similar issue, but the abs and epc light came on at once, along with 1 time randomly activated abs, which wasn't fun of course, apart from looking at the warning lights though, the car didn't miss a beat. I always have the scanner in the glove box, and it'd showed the YAW sensor intermitten fault, so I know it's need changing.
But as mentioned above, scanning is the first step. Also don't be surprised if a lot of fault codes will show, as the cccu can store old codes, if they weren't deleted before. So make notes of them, then delete, then scan again.
 
Sylvester said:
I've had similar issue, but the abs and epc light came on at once, along with 1 time randomly activated abs, which wasn't fun of course, apart from looking at the warning lights though, the car didn't miss a beat. I always have the scanner in the glove box, and it'd showed the YAW sensor intermitten fault, so I know it's need changing.
But as mentioned above, scanning is the first step. Also don't be surprised if a lot of fault codes will show, as the cccu can store old codes, if they weren't deleted before. So make notes of them, then delete, then scan again.
Click to expand...
Tip, when the scan is complete, click on the "Copy Report" button, and open word pad, and "Alt v" to paste the report into the text document, then "save as"
Mac.
 
Former Land Rover owner here - I only mention it because ABS lights were often triggered on my Discovery due to very slight variances in voltage detected from the sensors especially off road. Mud and road crud/slush could easily trigger the ABS warning with no permanent fault recorded. It's probably nothing to worry about but as others have said get a scan if it reassures you.
 
So this problem has escalated. We've been down to Bath today to meet up with my mum and sister. About 65 miles each way. On our way home, and (fortunately) taking the more scenic route up the A466 from Chepstow to Monmouth rather than the A449 from Newport. We've just gone through Tintern and the ABS light started flashing and I could feel a pulsing through the brake pedal, and then what felt like a decidedly mechanical knocking. Stopped immediately, if somewhat awkwardly, and switched the car off. On restart, the light immediately came on and the weird knocking/pulsing started up again. I have moved the car off the main road (the brakes "seem" to be working fine...) and have called out the RAC, who will be here in about 30th minutes hopefully. Further updates as they become available.
 
Hmm interesting one - will you report back once the culprit is identified? Sounds like a serious fault that I for one would appreciate knowing what it could be just in case the same happens to me!
 
OK, so of course the issue had self-healed by the time the RAC man had turned up. He did a visual inspection of wheels and front discs/calipers. Then we rolled the car back & forward, and had the wheels on full lock and then wiggled back and forth. The one thing he spotted was a small bit of the "lip" on the edge of the brake disc had broken off. The suggestion was that could have jammed in the abs sensor and the mechanical knocking noise was it catching the caliper as it rotated. Does that make sense?
As nothing was now showing Simon the RAC man said he'd follow us to Monmouth to see if it would reappear. It did not, so he then said he'd follow us home (about another 20 miles). Just as we peeled off down our lane, and Simon flashed his lights and drove on, the ABS light came on, but no banging/knocking!
So, we're home and I'm booking the car in to the garage to get the abs thing checked out.
 
Ken Long said:
OK, so of course the issue had self-healed by the time the RAC man had turned up. He did a visual inspection of wheels and front discs/calipers. Then we rolled the car back & forward, and had the wheels on full lock and then wiggled back and forth. The one thing he spotted was a small bit of the "lip" on the edge of the brake disc had broken off. The suggestion was that could have jammed in the abs sensor and the mechanical knocking noise was it catching the caliper as it rotated. Does that make sense?
As nothing was now showing Simon the RAC man said he'd follow us to Monmouth to see if it would reappear. It did not, so he then said he'd follow us home (about another 20 miles). Just as we peeled off down our lane, and Simon flashed his lights and drove on, the ABS light came on, but no banging/knocking!
So, we're home and I'm booking the car in to the garage to get the abs thing checked out.
Click to expand...
Hence the KKL cable purchase, perchance?
Mac.
 
I've literally had the same symptoms, as I'd mentioned it above.

The faulty yaw sensor activated the abs randomly, which was like a lot of scary knocking and almost felt like the car's gonna fall apart :eek:
Other times just the light came or with only 1 sudden shake.

Get the scan done, including abs system, and you'll see. My 2 cent is on the yaw sensor.
 
Ken Long said:
Will VCDS Lite show up sufficient information about ABS sensors?
Click to expand...
Even the free version will list every fault. The limitation is that only first error in each controller is described, subsequent error show error code only. Simple to get full details on Ross-Tech site. Just Google "rosstech P1031" for example, (FSIs only for that one though🤔).
Mac.
 
Sylvester said:
I've literally had the same symptoms, as I'd mentioned it above.

The faulty yaw sensor activated the abs randomly, which was like a lot of scary knocking and almost felt like the car's gonna fall apart :eek:
Other times just the light came or with only 1 sudden shake.

Get the scan done, including abs system, and you'll see. My 2 cent is on the yaw sensor.
Click to expand...
I'm hoping to either get across to @Erlingtheyounger for a scan, or to get a lead and use VCDS Lite myself. I will report back. The knocking does sound very similar to what you describe. Was it easy to sort the yaw sensor?
 
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