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Cruise control problems

marx3

New member
Joined
Aug 21, 2011
Location
Denmark
Who has the black belt in troubleshooting cruise control?
The cruise on my 97 940 FK / AW71 won?t engage.
I?ve done some trouble shooting: checking the fuse, checking for vacuum leaks, checking the servo, checking that the brake pedal switch holds vacuum.
I tried another control module, I checked the function of the turn signal stalk and I think it checks out.
I noticed I don?t have any voltage on the brake pedal switch, which is odd cause the brake lights work.

Can anybody point me in some direction?
 
My car has the OBD port in the center console and I don’t have the brains to fabricate a flasher for it.
Can you explain how to make one?

Btw my speedometer works perfectly and I also tried another cluster.
 
If you're sure about everything, recheck the brake pedal switch again. You can open them up, there's an O-ring in there for the pin that makes contact with the pedal.
In my case the O-ring was worn out and although when manually trying it it seemed to work, but when driving the cruise disengaged after 2-3 seconds.

Also double check that the stalk is OK.
The switches tend to wear out and/or lose contact.

If you mean the brake light switch for the brake lights (not the one for cruise), it has permanent 12v at pin 1 (Green-Yellow) and only closes when you press the pedal (see below).

See wiring and function diagrams from my 97/98 Greenbook below.

Guide for making an OBD reader yourself. Cruise is on pin 13.
https://www.volvoforums.org.uk/showthread.php?t=61562
https://www.volvoforums.org.uk/showthread.php?t=80007
 

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The stalk wires tend to break from flexing while the dimmer function is being used. Other than the vacuum switch leaking, that is the most common problem with the cruise control system on a 740/940 Volvo.
 
I have no power at the cruise switch on the brake pedal. Thats what puzzles me. I'll try and look into it tonight. Do any of you guys know what feeds that switch?

I'll try taking apart the stalk and see if anything is corroded or worn. As I recall, that stalk is getting 12 volts.
 
I have no power at the cruise switch on the brake pedal. Thats what puzzles me. I'll try and look into it tonight. Do any of you guys know what feeds that switch?

I'll try taking apart the stalk and see if anything is corroded or worn. As I recall, that stalk is getting 12 volts.

If you look at the wiring diagram I posted, the brake light switch is 3/9 and it's getting power from fuse no. 4.

Just to make it clear, the brake light switch (3/9) and the cruise vacuum brake switch (3/38) are two physically separate pieces.
 
If you look at the wiring diagram I posted, the brake light switch is 3/9 and it's getting power from fuse no. 4.

Just to make it clear, the brake light switch (3/9) and the cruise vacuum brake switch (3/38) are two physically separate pieces.

This. The switch you're looking for that controls the cruise has a vacuum line going to it.
Easy to test with Ohm meter, remove the 2 wire connector and see if it contacts. Pressing the pedal should open the contact. Another quick n dirty way to check is to drive on the highway and pull the brake pedal toward you while engaging the cruise control. Usually that'll tell you if you need to adjust the switch. It should be almost completely compressed if adjusted correctly IIRC.
 
Update: while looking for the missing high beam I took off the turn signal stalk and discovered a broken wire for the cruise control.
Fixed it and the cruise works perfectly :-)
Omg the stalk has many small parts inside.

Thanks for any and all advice
 
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