ABS and Batteries

[grey-vr6-dan 0]

I've been having an intermittent fault with my abs where the light comes on randomly and goes off if i reset the car. It was doing it everyday. I read somewhere that it could be the battery getting knackered so I swapped it for a known good car battery and the light didn't come on once for 2 days and the abs was working fine so I thought that was problem fixed until on the way home today it came back on again. Turned car off and on when I stopped at the lights and it was off again. Anyone have any ideas? Could the alternator be not working fully?

[dinkus 10]

The only way to tell really is to get it hooked up to VAG-COM and see what it tells you...

[Supercharged 2]

A Good battery and Voltage is important for ABS, worth measuring the volts across the battery terminals with the engine running to check the alternator output - should be 13.3 to 14.3 ish (around the 14V mark as opposed to 12.8 with the engine off showing a good, fully charged battery)

[grey-vr6-dan 0]

Just tested my voltages. All fine. Its weird that changing the battery fixed the problem for a few days.... does that throw any light on anything else? As for vag com, when the light is off there are no faults but if I scan it with light on I get a fault to do with valves, but surely it cant be becuase why would reseting the car fix the problem each time? When the abs is light is off it works perfectly and no amount of abs use will make the light come on, it just comes on totaly at random without even touching the pedal.

[Supercharged 2]

I'm not really sure tbh but wondering if it's one of those codes that makes the light stay on permenantly once triggered (maybe because it needs attention) - changing the battery reset it until it was tripped again...

[grey-vr6-dan 0]

I see what your saying but that wouldn't explain why the light goes off when the car is turned off and on would it?

 

Ive just been out driving and the light hasn't come on once (I still have the good battery in) so the battery has definitely improved it having only illuminated the light once in 4 days..... The old battery it would come on every day at least once.

[Skimask 0]

There are 2 multiplugs on your ABS pump - Disconnect them, have a look at the terminals and if needed clean them up. It sounds like a voltage drop triggering a fault code.

[dr_mat 0]

I see what your saying but that wouldn't explain why the light goes off when the car is turned off and on would it?

 

Ive just been out driving and the light hasn't come on once (I still have the good battery in) so the battery has definitely improved it having only illuminated the light once in 4 days..... The old battery it would come on every day at least once.

 

The ABS fault is recorded in the ECU, but every time you turn the ignition off and back on it will assume that everything is working again (otherwise how would it ever work?), so the light goes off - UNTIL it detects a fault, when the light comes back on.. This is quite normal.

I think it's just a coincidence that it worked for a few days when you swapped the battery. Get it VAG-COMed. Most likely you have a faulty wheel sensor.

[grey-vr6-dan 0]

As I say I've vag com'd it and the faults are about the valves but only when the light is on I get the faults. When the light is off the abs works perfectly!

[dr_mat 0]

As I say I've vag com'd it and the faults are about the valves but only when the light is on I get the faults. When the light is off the abs works perfectly!

 

Yep, the light comes on to tell you that it's not working.. that's what's supposed to happen.

 

If VAGCOM says it's the valves, then chances are you need a new ABS valve block. There's a slim chance you might have a wiring problem, or an ABS relay problem, but it's a slight chance. The good news is that ABS pump units are cheap and very reliable, so you can pick one up cheap and it's almost certainly going to be fine.

 

As I understand it, you will only have a "low voltage" fault from the ABS if the 12V line drops below ~8V, and you'd know about it well before that happened ... But you aren't getting low voltage faults, so I say ignore the battery and fix the ABS.

[grey-vr6-dan 0]

Thanks for the help. Its certainly strange because changing the battery definitly improved it loads.

 

What is the partnumber for the valve block I need too get? Does anyone have any going cheap on here?