300SDL ABS Light

[pilot53]

The ABS light on my 86 300sdl comes on as soon as the car starts, it doesnt have to move, what does this usually mean?

[Diseasel300]

Is the Airbag lights on or the Tach work? It could be a bad OVP relay. If the OVP isn't it, it could be a blown fuse, crusty connection (if you still have the aluminum fuses), or a fault in the ABS controller. Don't quote me, but I think you can pull blink codes from the ABS controller at the diagnostic port by the battery. I'm sure someone who knows more about the ABS controller will come along and correct me on that...

[TwoMuchBoost]

ABS before the car begins to move usually indicates a hard fault like low voltage/bad ground or module failure. Bad sensors usually don't show until car begins to move.

My ABS light will stay on for a quick second when my afterglow is active during cold-start idle. The 100amp draw of the glow plugs on top of just cranking the motor over will make the light stay on momentarily. Turning off electrical accessories or increasing RPM slightly off idle makes it go away too.

Take a voltage measurement at idle, anything in the 11ish range and under seems to trigger a light.

[pilot53]

Originally Posted by TwoMuchBoost

ABS before the car begins to move usually indicates a hard fault like low voltage/bad ground or module failure. Bad sensors usually don't show until car begins to move.

My ABS light will stay on for a quick second when my afterglow is active during cold-start idle. The 100amp draw of the glow plugs on top of just cranking the motor over will make the light stay on momentarily. Turning off electrical accessories or increasing RPM slightly off idle makes it go away too.

Take a voltage measurement at idle, anything in the 11ish range and under seems to trigger a light.

Interesting, I have now noticed that if I start the engine after the glow plugs have been used the light will come on after start and stay on. But if I shut the car down hot and start it immediately without letting the plugs glow the light doesnt come on. The tack works and the airbag light is out. Does this sound like the OVP, or maybe just a battery or charge issue? The battery has 12 volts with the engine off.

[Diseasel300]

The battery should be 12.6-12.8V with the engine stopped. Yes, that decimal point matters. If you have 12.0V, you have a charging issue or a spanked battery. And yes, that will set the ABS light since the voltage will drop below 10V when the starter is engaged.

[pilot53]

I just had the battery and alt tested, it came back good. Following the FSM troubleshooting steps for a light that stays on without a battery warning light points to either the ovp relay, abs relay, or a disconnected abs controller. I replaced the ovp and that didnt fix the issue so I will try the abs relay next. What is odd is that the problem now doesn't seem tied to the glowplugs or temperature, but is intermittent. I pulled the relays out a few times so maybe shaking them up has some effect.

[pilot53]

Originally Posted by Diseasel300

Is the Airbag lights on or the Tach work? It could be a bad OVP relay. If the OVP isn't it, it could be a blown fuse, crusty connection (if you still have the aluminum fuses), or a fault in the ABS controller. Don't quote me, but I think you can pull blink codes from the ABS controller at the diagnostic port by the battery. I'm sure someone who knows more about the ABS controller will come along and correct me on that...

By the way, what do you need to pull these codes?

[pilot53]

Update: I pulled the ABS relay and took it apart, did not find any apparent damage or issues with it but when I put it back together and reinstalled it the problem went away. Im guessing something in there was just loose.