TRACS/ABS: 70: intermittent abs coming on, light is out

[celticvolvo]

I have a 1998 V70 AWD auto estate, the abs and tracs lights go out normally and stay out, so far great!, but the problem is the abs comes on about 30mph by itself and starts pulsing, when you brake the abs is pulsing through the pedal. Tried resoldering the dodgy joints on the module to no avail. Mechanic says the reluctor rings are okay, but look rusty to me? Any ideas where to go now. The car is mint apart from this with only 83000 miles, it is due mot next week and I dont really want to scrap it, thanks

[Luxobarge]

Almost certainly reluctor rings IMHO.

The reason you don't get a fault light is that the ABS ECU thinks there's nothing wrong, it just sees a wheel "skidding" and does what it's supposed to do.

Hard to tell which ring it is, other than by inspection and judgement.

Cheers

[celticvolvo]

Can the abs system come on itself then if you are just driving along without using the brakes if one wheel appears to be rotating at a different speed to the other??

[Luxobarge]

Originally Posted by celticvolvo

Can the abs system come on itself then if you are just driving along without using the brakes if one wheel appears to be rotating at a different speed to the other??

Yes, if TRACS is on and it goes outside certain limits and definately if you press the brakes. As I said, the ECU thinks it's skidding, and both ABS and TRACS will do what they're supposed to do.

[celticvolvo]

if tracs is not on can the abs pump run of its own accord without me actually braking or is tracs permanently on in the awd volvos?

[doc_power]

Hello

Had a very similar problem on my V70 Phase I 2000, with around 100k

The ABS did the self test and went out, but came on after 30-50 mph


Before i found the problem i did the following:

1.) Resolderded ABS ECU
2.) Fitted New Passageneger ABS sensor
3.) Replaced both front ABS Relcultor rings
4.) Fitted 4 new tyres with same pattern

5.) the problem was when i was looking at were the ABS sensor was fitted on the drivers side, it was sitting slightly proud, with corrision A bit of sand paper around were it fits and problem solved.

A few other thingscome to mind -Does the Engine Mgt Light come on and is the speedo a bit jerky.

Hope this offers some help.

Best Regards
doc_power

[celticvolvo]

no management lights on except ETS now and again, speedo is fine not jerky, everything works great except that ABS comes on of its on free will whether or not actually braking?

[doc_power]

If the ETS light is going on and off, it suggests that it picks up the codes, but then clears itself.

The next course of action may be to read the codes, to see what is triggering the ETS light. This may point to the next course of action ie ABS sensor.

IF the ABS relcutor rings are falling apart, this can sometimes lead to a jerky speedo.

Doc_power

[Luxobarge]

Originally Posted by doc_power

The next course of action may be to read the codes, to see what is triggering the ETS light. This may point to the next course of action ie ABS sensor.

Eh? How could an ABS sensor affect the ETS light?? I suggest that there are two separate problems here.

ABS sensors or rings can affect the speedo, but only if the fault is on the front LH wheel, and even then only on later cars. This is the wheel that the speedo gets its information from.