The ABS light won't go off after start up. Last time I had this problem, the ABS used to go crazy after driving 50m, then the light came on and the ABS stopped working. I think I measured the sensors and found the rear left to be slightly off. Now the ABS does not engage when driving off, the light just stays on. I have a bluetooth OBDII-reader, can I use this to read the fault codes identifying the broken sensor? Seems like one of the sensors are not responding at all this time since the ABS just shuts off on startup. I also remember the sensor was a complete madness to change, had to set in on fire and burn it out.

I would clear all codes then take it round the block and re-read to see where you're up to 

To clear codes, is just pulling the negative connection to the battery for some time enough? Because a day or more this doesn't seem to help. Or do I need a OBD reader this? Can I use an Android app?

Depending on which fault in your system has caused the lamp to illuminate, disconnecting the battery may not extinguish the lamp if the fault is more than a sensor.  The system sees the fault as serious if it is a pump module or something of that nature and won't put out the light without proper investigation.

 

The safest and most accurate way to do it is to scan the car with an obd reader, provded the reader can read ABS codes, as some do not.

 

That way you can sort the fault or at least get an accurate location to start your diagnosis from.

 

Have you checked all your underbonnet strip fuses are intact and that one has not fell victim to a hairline crack at all?

The fuses on top of the battery? I checked them, but could not see anything abnormal. Is there an app that can read ABS fault codes via an OBD bluetooth reader?

To read the codes on the ABS you really need a VAG based reader that has CANbus like VCDS have a look in this 

 

To see if there is anyone near you that could help you 

Which reader can I buy that reads ABS codes and works with this car?

I got a VGgate VS450. It says ABS wheel sensor rear (G46)

00290-035

 

This was the sensor I changed the last time I had ABS problems, that time I measured it to find a problem with it. It had been working fine, but a sticking caliper has produced heat in the brake disc, it might have taken damage.

 

I tried to delete the code, the reader said it was deleted. I turned off the ignition but the ABS light was there. Also the reader showed the code again. Will try to swap it. Would it been one of the other sensors it would been a nightmare to swap, I literally burned the rear left sensor out.

5 minutes ago, RallyeSport said:

I tried to delete the code, the reader said it was deleted. I turned off the ignition but the ABS light was there. Also the reader showed the code again

Which proves that you have an uncorrected problem with the ABS.

The left and right side sensor is different right? The are sold as the same for both sides on ebay.

Are these rear sensor interchangeable right/left? I have one, but the sensor part i different top/botten, but the metall sensors goes through on both sides.

They are useful on both sides of the sensor, just turn it for the correct side left/right. Deleted the code after installation, worked perfectly with Vgate VS450 with no new warning light. Chiseled the old sensor out with a flat screw driver.