Hello, I hope this question hasn't been answered already...and if it has my apologies, but I can't find it in the search field. Facts, 91 740 turbo wagon 316 thousand k running strong as ever. The issues is with my ABS light. It was solid red when I purchased the vehicle, recently have new rotors and pads installed on front , just pads on rear. Since the break job the light is still red, however....aha... sometimes when I start the car the light isn't red anymore and the red OD arrow is now lit. When I press the OD switch to engage it the OD light goes out but the ABS light comes on and stays on. So after the third time this happened I left the OD switch alone and the ABS light stayed out for about 5 mins of driving and braking ... then the ABS light and the OD light started to come on very faintly and go out for the next 5 mins .Kinda on then off again. Till at last the ABS light began to become solid red . Is it a true ABS issue or a electrical connection issue? If it is electrical where do I start? . I tried to look for the green manual ( I think Pierce suggested those in a post) but cannot find them in a google search. Any way thanks for your patience with this newbie. Lots of good information on here.

 

Hm, I believe the OD and the ABS lights are orange...
Your problem is most likely in the instrument pod circuit board. It needs to be resoldered; pretty much all of the connections have to be refloated, everywhere where the wires poke through...
Do you have a working ABS while this is going on?

 

Hi lev, Yes the NORMAL everyday situation is that the ABS light is illuminated brightly. On the occasion usually on start up, the ABS light is out and the OD light is illuminated making me think the OD is disengaged until I actuated it then the ABS light comes on. And where would I find the instrument pod circuit board ? Doesn't sound like an easy place to get to. the OD light ( arrow ) is orange but the ABS light is red

 

The board is stuck on the back of the instrument pod and everything electric works off that...
Again: do you have functional ABS?
How are the rest of the warning lights? Fully functional?
All gauges OK? Speedo?

 

in addition to what lev asked...

does your overdrive actually shift into/out of OD properly? go 55 or 65 on a open highway, steady as she goes, press the button so the light comes on and the RPMs should go up 700 or 1000... press teh button again so the light goes out and the RPMs should drop back down to 2500 or 2800 or whatever is your normal at that speed.

and to test the ABS, on a dry smooth surface with no vehicles around, hit the brakes hard going 25 or 30 MPH, and you should feel the pedal 'throbbing' under your foot as the ABS engages.

 

Sorry lev misread your reply and forgot to answer your question about the ABS.. I thought you were referring to just the light, silly me . I don't know if the ABS is functioning. My guess is no. But I will check it out with Pierce's suggestion. I have never felt the pedal pulsate like it does on my truck from time to time that is also equipped with ABS. Sometimes when braking in the truck on bumpy surfaces it will pulsate so I assume it should feel similar if it happens on the Volvo. All of the rest of the lights and gauges are working properly and the OD does function as it should. I will also check the speedo against another vehicle to see if the readings are the same.

 

Do your ABS test on gravel or grassy or wet surface; much easier to induce traction loss than on dry, flat, etc.
Your speedo is fine apparently.

 

on my 740 T wagon, it takes some HARD braking to activate the ABS, that car is just planted on the road. of course, I have 16" wheels with 205/50 michelins, bilstein touring shocks, ipd sway bars and all new bushings all the way around. harshes the ride, but man it handles tight.

 

Ok... did the slam break test ....nothing but a small skid...the rears locked up. Speedo is working. I will try the test again the next time the light goes out to see if they work then. Just puzzled why the ABS light goes out and the OD light comes on. Is there a connection in the circuit board? a faulty relay ?

 

lights and circuits cross feeding each other often happen with bad grounds, but I'd have to examine these circuits carefully to try and find possible mechanisms, something I don't have time to do right now. I know the OD light is wired to power such that the OD relay grounds the other side to light it, but some of the other lights are wired to ground, and the signal input supplies the power

the ABS gets a signal out of the speedo module to tell it how fast the rear axle is turning (its a 3-channel ABS, each front wheel has a speed sensor, but both rear wheels share the same speed sensor, which is the speedometer).

 

Pretty sure it's the circuit board--it acts in mysterious ways... There is no easy way to figure it out precisely. Take it out, refloat ALL joints witha soldering iron. 99% chance that's the problem.

 

and, if you have no experience soldering on circuit boards, and don't know what reflow means, find a friend or someone who knows, bring it to them, you do need to know what you're doing to do this right.

you want a temperature controlled soldering station set to 650F, with a medium printed-circuit-board tip, and some fairly thin good quality lead-tin rosin core solder, like Kester 44, used sparingly to prime the tip and freshen joints.

I need to pull the panel on my 740 and do this.

 

Thanks guys....I will give it a try..sometime in the summer when the weather is DRY. I will gather the necessary tools and get some old computer boards to practice on. I am guessing that refloat means to make the joint molten. I will also check out some how to videos. Is there a service manual available to show where the board is located and how to remove? Thanks again for all the input.

 

It's no rocket science. Exactly, "make the joint molten"--good way to put it. I don't ever have to add solder, just hold the gun on the joint til it's molten. Little wires poke through and they have to be enveloped by solder; with time the contacts breaks, cracks appear, often visible... I wish I knew which joints control what but since I don't, I do them all. It takes 20 mins.

 

The one thing I have noticed is that the ABS light only goes out on start ups. Usually after I have driven it, parked went into the store or such then restarted for the next trip. I have also had some issues with the bulb failure light coming on when braking. Last night after a brief trip to the hardware store , I got in and started the car everything was good, no warning lights. The car drove good, but noticed it wasn't shifting into OD due to the higher than normal RPM's. The arrow light was not on indicating OD was off. I toggled the OD switch a couple times to make it shift and downshift and things seemed to be working. The OD light came on then off respectively . On the third time putting it back into OD the ABS light came back on and the bulb failure light when I braked, so I am concluding it is truly an electrical connection issue.

 

Actually when the OD light is ON, the OD is OFF! And yes, it all looks like the CB needs attention.