hello there,

i have this issue: when the Volvo is started(engine fired and running) the "ABS" and "BRAKE" lights stay lit. this is at idle. the lamps stay lit UNTIL throttle is applied, usually after 1000 RPM. Hot or cold, with rare occasions with a hot engine the lamsp do not stay lit on startup.

i've checked the connector at the ABS module under the dash, checked the wiring connections at the ABS pump. i have yet to open up the one or two realys there. also have not opened up the surge protector yet, but the fuse is alright. before i go ahead and either take the time to go through every ABS voltage/ohm test outlined in the greenbook or just install a new ABS pump module, i would love to hear/read whether this can be adressed here. i figure it will be easier to diagnose off-hand, if you will, seeing as how the issue has particular facets to which may outline the cause: the lamps stay lit after the engine is on, at idle. when the throttle is opened-up or engine speed increased past 1000RPM the lamps go out. every time. field voltage issue? faulty pump test/lamp disable?

Volvo in question: 1991 744 turbo.

 

Don't install a new module, it won't be the issue. It takes a pretty fundamental issue with the ABS system to disengage the whole thing on initial startup.
The ABS system is VERY sensitive to low voltage, anything below around 12v will make it disengage the system. It is a safety feature, better no ABS than maybe ABS when you need it.
So, you can sort of see where I am going, how is teh battery voltage at idle?
Also, I believe the 1991 was the change over year to the new ABS system, you might have ABS diagnostics on board? If not, I have teh exact same ABS system as you and spent ages running through the system on my car, so I can suggest you start with the basic diagnostics, check battery voltage at module, surge protector etc as per Green book. The initial power supply/ earth testing will only take you an hour or so and are usually around 80% of teh failures in my opinion.
I would also check the ABS power supply relay on teh pump, it is an on/on relay, one side supplies 12v and the other lower around 5v. If you put power and ground to teh relay terminals you can measure teh output at each output terminal (just look at the terminal map on the back of the relay to connect the wiring up properly).
The Greenbook description and process is very convoluted for testing this component and is a reasonably frequent failure point.

Regards, Andrew.

 

hey man,

thanks for the input. my voltage is normal at ~14.2, looks like i'll be having loads of fun now checking through the relays and grounds. ha.
and yes, as said previosly my ABS system was not upraded with the new system. i'd like to change it over though. anyways, i'll check it out here.

thanks man.

 

Changing the system over is not easy, completely different pump, wiring connectors etc.
Have fun, it's a little time sconsuming but not that hard to diagnose the system, the worst part is getting to the module under the dash and exposing the terminals to use the multimeter.

Regards, Andrew.

 

so far i've concluded, more or less, it's the valve relay. there was no 'click' when i grounded #27 at the connector. i'll replace and see what's what.