ABS Light On - FIXED!


87 928 S4 Auto. For some time I'd had a constant ABS light. Comes on when you start the car, before moving. Not passing the initial self check. Even so I went through and checked the wheel sensors with a ohm meter, pulled each one to check and clean the sensor and toothed ring. Jumped the relay, checked the fuse, nothing.... Light stays on. Was reading the WSM last night on ABS and it didn't give me much to go on. Started to suspect the ABS brain, but how to check? Looked at the wiring diagram, maybe I could check to see if the signal was getting to the brain? Noticed there was a junction marked ABS ground. Maybe I'll go check grounds as well. Come to find out while poking around the ABS pump under the hood I noticed two wires that went to a juction, wiggled the wire and they were loose at the junction. Pulled that apart, cleaned up, put some dielectric grease on and re-assumebled. NO MORE ABS LIGHT! Turned out to the be simpliest thing. All hail the grounds...


make sure tha battery is disconnected before you remove or tighten the screw otherwise you will burn a hole into the edge of the fender, and possibly fry some other wires, this wire is usually removed when the timing belt is replaced, as its part of the engine harness, it is supplied by battery voltage
Very good find.....my 1st thoughts were RELAY.....mine slowly died...causing an intermittent warning...but was an easy fix on the CE panel....there also is 2 relays on the ABS pump that can and do die as well.....those are harder to check, since often they are model year specific....so unless you have a working same model year to swap with you just gotta buy the relay to test it...which is a bummer...
I had the same issue this week as Blackshark with the ABS on my late 86 Euro S2. (this has same ABS as the early S4s).

The light came on initially while driving. When the car was switched off, and then started, the light was on before the car was moving. So I reasoned that the issue might not have been a sensor problem, but perhaps a power supply problem.

I check ed the ABS fuse, then bench tested the ABS relay. both tested good.

I then found this thread, and cleaned up the 12v terminals he mentions, one of which looked somewhat corroded. To do this, I had to disconnect the battery ground strap....

When I put everything back together after cleaning the terminals, the light was off, and stayed off during a 10 mile test drive.

I am not fully convinced the dirty terminal was the cause of the light coming on.
Good question John, here's my experience:

intermittent ABS warning light, sometimes on after a few KMs sometimes on start up. replace ABS relay on CE, solved.

same problem returns 2 seasons later, clean all wheel sensors and rings, prob remains...........replaced pump and brain relays (the ones under the LH front wheel liner), prob remains..........put the old OEM CE relay in..........prob solved...............I got another new CE relay and alls well since.

And Brians absolutely correct; these relays are MY specific.
The relay is number XV in a GTS, and looks like this:

It is like a normal 53 relay but has an extra zener diode (22v, 15v possibly??) for suppressing spikes on the 12v. If the relay fails you will get alarms also when not driving.
The relay rating is unknown, but must be well over 15A since fuse 28 is a 15A type.

The purpose of this gizmo is that if your alternator goes haywire, and its output voltage goes up to a high value (like 20~22V) -- i.e., if a high voltage appears on terminal 30, the Zener diode goes into conduction, which lets a big current flow from terminal 30 to terminal 31, which (intentionally) blows the 15A fuse -- preventing the (undesirable) high voltage on terminal 30 from reaching terminal 87 (and the voltage-sensitive ECUs). You could also say that this gizmo "protects" the voltage-sensitive component from an overvoltage condition -- hence often called a "Protection relay".

A current draw due to the Zener diode leaking might cause battery drain.
Woohoo - ABS fixed and why you can't use a 53 Relay as a substitute for the ABS Relay


After 9 years of owning the 88SE I finally fixed the ABS.

When I bought the SE I knew the ABS had a fault and I knew it was a sensor as the warning light didn't come on until you had driven a few yards and exceeded 6kmh. I lived with it there was always something more important. I hadn't even noticed that the faults had escalated into a instant ABS fault. Prompted by failing the annual inspection here in Oz where they recently changed the rules (If it has ABS it has to work) I set about some diagnosis.

Checked the resistance across sensors measuring at the ABS brain multi-plug - 3 were around 1k ohms and were open circuit to Ground OK. Right rear was open circuit. Checked it at the sensor connection at the wheel and got open circuit across the pins and a short to ground on one pin. So bad sensor and some dodgy connections ? as well. I then checked contintinuity between the multi plug and the sensor connector on the wheel - 1 open circuit 1 connected wire. Pulled apart the connector in the spare wheel well and got good contintuity to both multi plug and sensor, reconnected the spare wheel well connector and continutuity was restored to normal. Thats a start.

Drilled out the old wheel sensor and replaced it with a used on I had from Eric in NZ (Dragon) 's parts car (Thanks Eric) and rechecked the system - Still an instant error.

OK next suspect is the CE panel ABS relay XVII - Pulled that and tested it with 12V across 31 and 15 got me zero resistance across 30 and 87. put that back and concluded it was OK. Big Mistake. I should have checked I was getting 12V at the multi plug on pin 1.

I then wasted about 4 hours getting to the ABS Unit in the wheel well, pulling the relays and testing them, checking continuity between the Multi plug and the 12pin plug on the ABS unit, concluding nothing was wrong then reassembling it all. Sounds easy but you have to do all this with your head in the wheel well up against the ABS unit - so you have line of sight to the plug your head has to be very close to the unit - I need reading glasses.

Back to the CE panel - finally occured to me to check for 12V at Pin 1 of the Multi plug. Zip - Zero - Nada - Nothing - 100% of bugger all. OK ABS relay again remove it check it on the bench appears to work as it should. Lets try a 53 relay, even better use the reverse jumper - a piece of copper can't go wrong can it. Still no 12V at Pin 1.

Took a longer look at the ABS relay - Functionally it's no different to a normal 53 relay it just has a resistor between pins 15 (+12V switched) and 31 (Gnd) and a Zener diode across pins 31 and 30 (+12v unswitched) to protect against voltage spikes.
* Then I finally realised - while physically the pins are the same layout as a 53 relay they don't have the same * * electrical function. *

Made up a jumper and connected the real pins 30 and 87 at the relay socket - 12v at the multiplug, and Yippee no ABS warning.

You can't leave the jumper in as it leaves the ABS powered up with the ign off. Fortunately my pal Hilton (Xlot) had some spare ABS relays he acquired cheaply. Problem solved.

So that's why the ABS relay is $90 versus a 53 relay costing about $4 plus the cost of a Zener - about $2.

It should be possible to rearrange the wires in the relay socket to use a 53 relay in the socket and then add the Resistor and Zener externally. I'll pull the old relay apart to see what the values are.
Jon in OZ