I have a 13 yr old Audi A4 1.8 petrol and for some time now the ABS light comes on at speed and the brake pedal pumps and kicks back a low speed. I have taken it to the garage several times and they say have stripped the entire brakes, wheels etc etc but say the sensors appear fine and there is NO fault showing up on the diagnostics?? The say its either electrical or maybe to replace the ABS pump although there is no fault showing up for this? Can you shed any light on this, the car has done 160,000 miles?. I carry children in my car as part of my job and need to know if there is any danger regarding this? Thanks Paula
Hello and thank you for allowing me to assist you with your problem. Paula, the ABS sensors are probably ok if there are no diagnostic trouble codes in the ABS module. However, there could be a wheel speed that is a little faster or slower than the other wheels. This would make the ABS think that one of the wheels is starting to skid/lock up and go into an ABS mode, and that is why the pedal does what it does at slow speeds. There may be a tone wheel that is damaged, or something as simple as mismatched tire sizes. What the shop needs to be sure of is that all 4 wheels are reporting the same speed at all times to the module. If one or more sensor(s) show a different speed, then closer attention needs to be paid to that wheel in question. One tyre that is worn more than the others could cause this so keep that in mind. In the meantime, the ABS can be disabled by removing the fuse for the ABS module. This will keep the pedal from doing that kick back. It could be a module, but make sure that the garage checks the items I mentioned.
I hope this information helps, and let me know if you need further assistance with this.
Thanks for the advice Chris, I just spoke to the garage and they told me that if one of the wheels were running at a slower speed then it would have been reported during the Bosch diagnostics. The tyres are fine, although I have noticed that the back left tyre loses at least 10 bar within a few weeks and the other tyres lose only 3-5 bar...dont know if this is an issue?
Once the tyres are inflated correctly, the ABS light still comes on and the pedal still kicks back. As long as its not DANGEROUS to continue using the car, I will not replace the ABS pump as the car is so old I dont see the point?
Would you say it is safe to continue using the car in this state given that no faults have shown during the diagnostics?
Thanks in advance - Paula
Ok Paula, then if you are not going to fix it, then what I recommend doing is to have the ABS system disabled by pulling the designated fuse, or disconnect the ABS module connector. Now this may turn the ABS light on, but it will prevent the pedal from kicking back, and the brakes will operate like you do not have ABS. This may be the safer solution.
Hi, thanks again for your advice, I have spoken to Audi and they have said that its highly unlikely to be the ABS pump but mentioned that it may be the CV joint as there are these rings inside it which may be broken and cause the ABS troubles that I am experiencing. I just need to decide what it is that I need to do to sort this car.
You are welcome Paula. Yes the "tone ring" I mentioned earlier is what the folks at Audi are talking about (in the CV joint). I agree with Audi that it is not the pump.
Good luck, and if you need further assistance, please let me know!