E39 ASC and ABS Lights on

Andrew Rolland wrote: A neighbour who is a mechanic suggested taking it out on the back roads and slamming the brakes on to get it to lock up and that might 'somehow' cure the fault.  He also implied that even though the lights were on in the dash there would still be a degree of ABS breaking. He also said that if you slam them on hard enough and the wheel which has the faulty sensor would lock and from looking at the skid marks on the road you could tell which wheel had the fault. Anyone else heard this? Andrew

Apart from flatspotting your tyres i doubt if locking them up would make any difference.

As for which wheel locks points to the faulty one, The reason the lights are up is to tell you the whole system is disabled. Hence when you press the ASC button the light comes up on the dash to tell you you've disabled it.

It would never just disable the ABS on one wheel. God forbid you have to break suddenly, one wheel would lock, the other wouldn't and you'd end up either in a ditch, up the pavement or into the path of oncoming traffic. It would pull to one side the same as if one caliper was disabled.

Andrew Rolland wrote: my money is on the front left wheel sensor.

T'is a good job I'm not a betting man then!

Diagnostic check at local garage (£40) informed me that there was a fault with the front RIGHT sensor (o.k. easy to fix) and the main computer. 

The mechanic said he is 99% sure the computer error is caused by the wheel sensor fault.  The wheel sensor fault was confirmed by a manual check by checking the resistance of the front offside sensor with a multimeter and he said it was an open circuit indicating a fault.

I said that the ABS worked intermittently and he said chances are then that the computer was o.k.

When I told him what my neighbour had said followed by my skid, he said that the left front would have locked up to compensate for the loss of ABS braking on the front right.

So I guess if I had had the time (more like my fiancée letting me) I could have put a multimeter across each wheel sensor to find the faulty one but I wanted a double check as both ASC and ABS lights were on.

Front wheel sensor duly bought from ECP change from £58.  Will fit it on Saturday.

Andrew

?? does anyone know if any other model use's the same part?

i'm just of the phone to a local place and he can plug my car in for a check and he said he has a couple of BMW's for breaking but none are 5 series, but if the snsor's are any good i can have em for nothing  , i'll go along for the check anyway and see how it fair's out? 

Hi Andrew,

best thing you can do is listen very carefully to everything your neighbour and that mechanic tells you and then believe the exact opposite

Slamming on the brakes will make no difference.Once the MIL (malfunction indicator light) is on then the whole ABS system is shut down.A code for a wheel speed sensor will not cause a faulty module code. Your car has inductive sensors so will always measure open circuit.

HTH

Alan

Hi Ian,

Do you mean that they could communicate with the ABS but it showed that there were no faults or that they could not communicate at all?

Did they try and communicate with any other modules?

Any idea what scan tool they used?

Alan

Well my ASC and ABS lights now only come on when the engine starts and go off after a second or two as they should!

Here is how I did it.

Disconnected the battery.

Jacked up and removed front offside wheel.

Turned steering wheel to full left lock to get the best access and then I found it easiest to lie on my back with my head and shoulders under the hub.

Wire brushed the two mounting bolts clean and then tried to get the 5 mm Allen key into the bolt heads, it refused and I had to clean out the bolt head recesses with a screw driver then gently tap the 5 mm Allen key into the bolt head to ensure a proper fit as I didn't want to chew the bolt heads.

Both bolts removed easily without the need for WD40. The sensor actually broke up when un-screwing the bolts, there are two metal inserts bonded into the plastic sensor body which the bolts pass thru, both these inserts came away from the main body of the sensor.  In other words there was no way the sensor that came out would go back in!

Sensor was stuck in the hole and had to be pried lose then it just dropped out.

Cleaned up the area around the hole and wire brushed the mounting bolts clean and greased them up when I put the new sensor back on.

The most difficult thing was squeezing the rubber mounting bush on the cable into the support bracket bolted to the hub.

Refit wheel and torqued up bolts and reconnected the battery.

Lights stayed lit until I drove the car 50m. 

All clear, no faults, tranny shifting fine.

Job done by myself for a total cost of under £100 inc diagnostic fee.

Andrew

PS This method of checking which wheel sensor is defective by measuring the resistance of the sensor is rubbish.  Both the defective sensor that I took off and the new one had a resistance of 6 Ohms!  So in other words I couldn't prove the diagnostic check!