Erratic ABS?

[_KA_]

Hi. (always a good start) :wave:

I have a 05 Partner 2.0 HDi 4x4. Lately, the ABS seems to have gotten ideas of it's own. I first noticed it while driving in the rain; when braking, the ABS kicked in just before coming to a standstill and the rear end lifted. At first I thought the road was very slippery, but as it happened on dry roads also, I ruled that out.

Then, the next day, which was dry and unny: everything was back to normal. Next time it rained, same behavior. cratch:

I tried cleaning the sensor rings with pressurised air, but it made no difference. And last night, after starting and driving 50 meters, I heard a beep and the ABS light and STOP light came on. I returned to home base and took the C1 to work.

Today, everything seems to be ok again. And no error codes. I suspect one of the sensors.

I did quick forum search tudy: but couldn't find any solutions. Is there a kind soul out there that could point me in the right direction?

[crickleymal]

Is it the ABS or the rear brake pressure limiter? I may well be wrong but isn't there something that limits the rear brake pressure if the back lifts too much and this could be out of adjustment. Although why you'd need something like that with ABS beats me. Sometimes the ABS light comes on if the brake light switches aren't properly adjusted.

[addo]

Are the rear brakes working correctly? It sounds as though the ABS was responding to front brakes doing more of the work than intended.

[corkgsxr]

First thing id do is a full fluid change. Recommend every year on some vehicles to keep the abs right

[evdama]

A bit off tangent maybe but when I had my 2010 Mk3 I was running down some odd scrag-end tyres to get a spare set of steels from them.
At one point I had 195/55's on the back and 60's on the front.
The abs went haywire in the exact same way as the OP describes with the anti lock cutting in and the 50 yard warning lamps.

I think the system thought that a skid was in progress because the wheels were spinning at different speeds

[_KA_]

I asked to importer-owned local dealer and they thought it very unlikely to be anything mechanical. Like me, they strongly suspected one of the sensors. Or the wires and connectors. They also said that it could be any of the four sensors, as a fault in either one would disable the ABS and give the rear end lift.

The best way to check the sensors, unless they're obviously corroded or something, is apparantly to hook them up to an oscilloscope, turn the wheels and look at the pulses or lack of pulses. Otherwise, I would have to take them out and inspect them visually.

I do happen to have an oscilloscope, but everything seems to be ok now. So I haven't bothered. Hopefully, the pressurised air did the trick. If it happens again, I'll let you know.

[_KA_]

I think you can mark this as solved. Haven't had any more problems.

[_KA_]

Heh. It happened again... :S

I've had forever enough of lying under old cars in the middle of winter, so I took it to Peugeot. As expected the (rear right) ABS sensor was corroded. They replaced it and everything is back to normal. For a given value of normal, that is.

[ron]

First thing id do is a full fluid change. Recommend every year on some vehicles to keep the abs right

With you 100% on that.The ABS piston block is to such fine tolerance that moisture absorbed hygroscopicaly can rust & sieze the pistons on certain systems.alut: