S40 V40: Speedo & ABS

[Richard1]

I have an intermttent fault whereby the speedometer reads zero and the ABS warning light is on. When the speedo is workng normally, the ABS light is off. I've not seen any other combination. Either The car drives okay and the brakes work, indicators and lights okay. No other warning lights on. I have to estimate speed based on the rev counter. I haven't yet worked out what happens to make them work again. Bumpy lanes and humpback bridges have no effect.
The car's booked into our favourite independent on Friday, but thought I'd ask on the off-chance if anyone here had seen these symptoms.

[bobthecabbage]

Originally Posted by Richard1

I have an intermttent fault whereby the speedometer reads zero and the ABS warning light is on. When the speedo is workng normally, the ABS light is off. I've not seen any other combination. Either The car drives okay and the brakes work, indicators and lights okay. No other warning lights on. I have to estimate speed based on the rev counter. I haven't yet worked out what happens to make them work again. Bumpy lanes and humpback bridges have no effect.
The car's booked into our favourite independent on Friday, but thought I'd ask on the off-chance if anyone here had seen these symptoms.

Speedo pick up on the diff (I guess) or a wiring fault between there and the instrument cluster.

I would guess that without input from the speedometer the ABS won't work hence why the ABS light comes on.

If that is true then it would suggest that as neither ABS or instrument cluster is getting a speed signal in which case the issue is likely to be the speedo sensor or wiring fault from it to wherever it goes first (ECU?). I would be checking connectors and continuity of earth for the sensor as a first port of call. Sensors are usually held in with one bolt and can be removed from the gearbox so you can spin the gearwheel and see if anything happens (or your assistant can). I presume the sensors are electro mechanical but maybe they just have a magnetic pickup?

[gatos]

The speedo gets it's signal from the ABS sensors on the hubs, which are also speed sensors. So my guess is that one of your ABS sensors has failed. Ideally, you should get your codes read and it will point to which sensor is faulty. Also, you may be very very lucky and the ABS sensor is not faulty, and instead there is corrosion on the connector. A bit unlikely, but you have nothing to lose by checking them

[v40alex]

Check the sensor first but this can also be the wiring loom under the radiator corrosion.

[bobthecabbage]

Originally Posted by gatos

The speedo gets it's signal from the ABS sensors on the hubs, which are also speed sensors. So my guess is that one of your ABS sensors has failed. Ideally, you should get your codes read and it will point to which sensor is faulty. Also, you may be very very lucky and the ABS sensor is not faulty, and instead there is corrosion on the connector. A bit unlikely, but you have nothing to lose by checking them

You learn something new (almost) everyday!

Its a shame that I forget several things too.

Still can't work out why these sensors are about £100 each (bit less maybe) when other vehicles are about £40 max!

[gatos]

Originally Posted by bobthecabbage

You learn something new (almost) everyday!

Its a shame that I forget several things too.

Still can't work out why these sensors are about £100 each (bit less maybe) when other vehicles are about £40 max!

To be honest, I actually thought that ony the front Driver's OSF ABS sensor was used to measure the vehicle's speed. Then I checked VIDA and it was different. Indeed they are very pricey, but you can source second hand ones for a lot less. Rear are fairly easy to remove and replace. The problem is with the front ones. Many years of abuse and they are a real PITA to get out without damaging them.

[Baffler]

Originally Posted by Richard1

I have an intermttent fault whereby the speedometer reads zero and the ABS warning light is on. When the speedo is workng normally, the ABS light is off. I've not seen any other combination. Either The car drives okay and the brakes work, indicators and lights okay. No other warning lights on. I have to estimate speed based on the rev counter. I haven't yet worked out what happens to make them work again. Bumpy lanes and humpback bridges have no effect.
The car's booked into our favourite independent on Friday, but thought I'd ask on the off-chance if anyone here had seen these symptoms.

I had the exact same symptoms on my '98 V40 T4 which, due to the ingress off water through the multiplug connector, turned out to be a faulty ABS system controller (the black box on the ABS pump). Sourced a controller from Gatos, which I believe was from a low mileage '02 car, aaaand Voila! No more issues!

[gatos]

Originally Posted by Baffler

I had the exact same symptoms on my '98 V40 T4 which, due to the ingress off water through the multiplug connector, turned out to be a faulty ABS system controller (the black box on the ABS pump). Sourced a controller from Gatos, which I believe was from a low mileage '02 car, aaaand Voila! No more issues!

Very good point indeed Baffy. Completely forgot about that....