This ABS light is driving me crazy

I mean Mat, sorry.

Cleaning those contacts is a good call. Most quality multipole connectors use plated pins, usually over brass, a silver alloy is favourite. Quality contact cleaners are the ones to chose & they can be expensive. Do not use WD40 (The Sperm of Satan), it is not a contact cleaner & can attach certain plastics, it is designed to dispel moisture, it is not even a lubricant by design, although it does a reasonable job for a short while. Serisol was widely used in the electronic service trade, when people had things repaired, those with long memories may recall those days.
I use Electrolube or Deoxit F5, both are good & both are expensive; neither is guaranteed to be 100% successful, but unlike WD40 the results will be an improvement.
M

Hello members. Been absent for a week, lots of work. Thanks M. for the info on contact spray. Yesterday I changed the brake fluid which must have been very old. Took the car for a spin, abs-light still on, but after some kms light out! Some kms to the gas station, engine off, took some petrol, engine on, abs-light still out. Happiest man on earth! Driving home, light off. Went to friends in the evening, engine on, light on. Stayed on for 30 kms. Spend the evening with friends, back home 30 kms light on all the way. This morning started the car, light off. Plugged in pscan, abs no errors, circuit no interruption, with contact on I pushed the car by hand, all four wheels gave the same speed. Unplug pscan, start engine, light still off. Took a coffee, start the car, light on. Going completely crazy now. Sensors are new, circuit is OK, contacts are clean, brake fluid is new, front discs and pads are new, reluctor rings seem ok, pscan gives no error, wheels are responding, the car is braking fine. I just want the light to be off for 15 minutes to validate the "controle technique". Thought about taking an appointment say at 10, going there at 9 and drive around the controle technique center till the light goes off, and then pray it will stay off for 15 minutes.

This is a total guess, so I hope doesn't waste your time but here goes....

Have you considered that the fault might be elsewhere?

For example, what are the conditions that can cause the ABS light to come on.

A fault condition from the ABS unit is the obvious one, but what about if the ABS unit has no power?  What about a bad connection from the ABS unit to the dash?

Maybe you can do some experimentation.

If you pull the ABS fuse does the dash light come on?

Maybe your fault is in the ABS system, but maybe it isn't.  Think about any and all scenarios that make the light come on and see if it is one of those scenarios.

It also seems to me that he fault must be electrical. I did the pscan wheel speed test when the abs-light was off by pushing the car by hand, ignition on. With the engine on the interface freezes, there are no readings. This is normal I presume. I will do a wheel speed test when the abs light is on, to see if there's a difference. And then focus on the wiring from dash and fuses to the unit. Makes me think of The French Connection when they rip a car apart to find the drugs. I feel I will dismember my car to find the leaking wire. Thanks for your support!

I read a post on the internet from a guy who's been chasing an abs light for a year now.

This is an absolute guess or speculation “from out of the blue”.
Would ABS sense different rotational speeds when not braking and if so would it matter if tyres were different across an axle due to pressure variations or similar?

Thanks Delbourt for the suggestion. A friend of mine driving old minis also suggested this, but the tyres are new and the pressure is equal on all four. On the other hand, I drive a Ford Focus with abs, the other day a tyre was at 1 bar cause of a leak, but the abs light didn't came on. I suppose the abs senses more a discontinuity in the signal then a slight difference in continous wheel speed for the light to come on. But now for the amazing rebound in this abs sitcom. Last weekend when I turned off the engine the abs light was on. Yesterday morning, I started the engine again and the abs light was off, all by itself !!! Turned engine off, then on again, light still off. Went for a 30 kms drive, light off. Returned in the evening, light off all the way. This morning I drove the car, light off. The only explanation I can think of, is that the new brake fluid reacted on the abs unit and liberated the hydraulics inside... For now I am really really happy!!