ABS decoding
I am the third owner of a 1993 Vauxhall Senator 3.0 24v with 52,000 miles and history. It’s my third Senator and the best yet, however the ABS light is illuminated. To start with, the light came on now and again, but now it comes on as soon as you pull away. No one locally can read the codes due to the car’s age. I’ve been told you can ‘flash read’ them, but I’m not sure if it will damage the ABS system – there’s conflicting advice on the internet. I’ve spoken to a number of local garages, including an outfit that was a Vauxhall dealer until recently, but none will take it on. Neither will a local auto electrician.
Are you aware of a scanner suitable for my car, even if it’s an older type? Is it safe to use a paper clip to ‘flash read’? Which pins read the ABS? Without a scanner, what’s the best way to solve my ABS problem? I have a multimeter, but I’m not particularly proficient with it. Chris Jenner
The data from Vauxhall states that the ABS on your vehicle has no self-diagnosis feature and can only be read using the Vauxhall Tech 1 diagnostic equipment, although the updated Tech 2 should also read the system. The cheapest of these I could find costs around £300 – looking on ebay, secondhand units seem scarce and most are from overseas sellers.
Before going to such expense, I would carry out a few simple checks. First, ensure all tyre pressures are even. Next, check the condition of the earth points on all ABS components. If no problems are found here, you can move on to a couple of simple tests.
The first and easiest test would be to use an ohmmeter and check the individual sensors. By unplugging all four sensors and checking continuity with the meter, any sensor that shows a variation in its reading would normally be considered faulty. Then, by connecting a digital voltmeter and spinning the wheel
by hand, you should get a reading of 0.3-1 volts. Again, any variation will highlight a faulty sensor or pick-up ring.
According to the circuit diagram I have, the ABS ECU gathers information from the alternator and brake light switch. With this in mind, I would check that the alternator voltage is stable and also consider replacing the brake light switch; these are common problems affecting many ABS systems. There are also three relays fitted to the ABS system and checking the operation and connections of these would be a good move.