I have a 940 with non functioning cruise control. At first I checked the vacuum pipes. Vacuum bellow had pipe and the pipe from pedals were under brake booster, but had no T fitting. Vacuum pump had no pipe at all.

So I got new pipes, and connected them . Vacuum pump to T junction and bellow to other T side and from pedals to other. I also sucked the pump pipe before fitting. Vacuum bellow retracted, and engine speed rised. Also it seemed to keep the pressure, not losing it.

So I go for test drive. Result -> cruise not working. I thought about reading code from the led thing. But the led thing has no B box, only A box. I think that this car is so old that diagnosis for accessories is not present?

After that I took the kickpanel down. I took the cruise control stalk connector open (4 poles), and with beeper tested it. It seems to work. When off, no connection on any 4 poles. When on, 2 of those are crosed. Also, on ignition one of them has 12 V. When pressing set speed, 3 are crossed. So I think cruise stalk is ok.

The main unit is VOLVO 3501472. It has two connectors. 1 with 1 wire and other with 8 wires. For the life of me I could not figure out how the 8 wire connector is supposed to come loose. I did not want to break it. If someone knows how to remove it, please tell me. My idea is that with connector removed, I could somehow test the vacuum pump? it has 3 wires coming from the unit. Of course how to test it, if someone knows that?

Next I thought about the clutch and brake pedal switches, maybe those are at fault. On sidenote, brake pedal has two switches, one for CC and one for brakelights? I took the CC switch connectors from both pedals off and tested them with beeper. Both switches are closed when pedal is not pushed. When pedal is pushed, switch opens. I noted that the brake pedal switch has a wire,about 10 cm with abiko steal connector ( so it has female AND male ports) that is not connected anywhere? Maybe that is the problem then? But I could not found any connector that seemed to be missing? So where that wire should go? Here is and image of the connector. Wire color is Blue Red.




Does anyone here have the correct wiring diagram for -91 940? I found online 1994 diagram, but that has different CC main unit with 12 connectors. So that diagram does not work for me.

 

Do you have good brake lights? Make sure you do or no CC. If not, check the Check Light relay, the big red one.
Did the CC just quit or? Is the stalk switch good, those get dirty, and stick.
These CC are pretty reliable, usually it's something simple.
Check the fuse, #10? A blue/red wire is supposed to go to the fuse box...

 

is this a regular 940 (gl, gle) or a 940SE ? the "SE is really a 960 in many ways but has the 4 cyl turbo motor. I suppose with a manual its almost certainly a base model 940.

those cruise control units often crap out with age, they are fairly analog and capacitor values drift and just stop working right. anyways, here's the diagrams from the 1991 940 greenbook. any wires shown as RED are hot when the switches are set in the position shown.

 

Pierce, thank you for that. Mine is GL i believe, imported from sweden. fuel injected 2.3 non turbo, m45 (button 5 speed) gearbox.

That is the same 1994 wiring diagram that I found. But that is for different main unit, it has more pins than mine. Mine has only 9 pins. I believe that in 1993 when they added the B box to the LED fault indicator, they also added the option to diagnose the CC system. And that needed another CC main unit that HAD the option to diagnose. And B box has a pin for it. But mine 940 is so old, it has no B box, only A box.

 

Sorry should have said that on my first post. It is a sedan 940 with three brake lights. All brake lights work ok, when pushing pedal.

The light malfunction incator light is on always even when all bulbs are working. So I just took the bulb indicator bulb out. It annoyed me.

Also in my first post, I checked the stalk operation via the 4 pole connector. "OFF", no connection. "On" poles 1 & 2 are connected. SET SPEED poles 1,2 and 4 are connected. So in my mind stalk is working as it should.

 

fyi, those diagrams are specifically from the 1991 greenbook.

 

Ok, then it seems that there were different versions available? Because mine has 9 pin connection to the CC ECU. Heres image of the ECU

 

Sure - three wires go to the pump take two jumper wires and apply + and - 12 volts. Pick two connectors to run the pump, the third opens or closes a valve to hold vacuum. You'll get either a click or a running pump. Have replace a few bad pumps (years ago) if it wasn't a vacuum leak.With vacuum lines connected you can run the pump and watch it open the throttle - and close the vacuum valve with the third wire to make sure it holds vacuum.

 

hmmm, the 9 pin cruise control was apparently used on 240 and 740's.... I do not ahve 740 diagrams (other than the 91/92 model years that were essentailly the same as 940), but I do have 240's and indeed, the 1990 240 (year picked arbitrarily) shows a 9 pin, like this...

 

There are two versions for the 740/940 CC line, 1991 and earlier, 1992 and newer, when dash changed. The 1991 uses a much smaller unit, not sure about all the rest of the CC components.
BTW, is this a manual tranny car, as in with a clutch? Because 940 was never offered with a stick in the US so if yours is a manual, then it's a conversion and the CC is a little different (another dump valve at the clutch pedal)...

 

The OP profile lists being from Finland

 

I don't see it in these diagrams, but the vehicle-speed sensor is an essential part of the cruise-control system.
Does the speedometer/odometer work?

 

Update on the situation.

I took the pump out to test it. First put +12 V on Yellow / Red wire and ground to green. Pump starts, but does not make any vacuum. So I thought that the pump is somehow broken.

I don't know why, but I tried to ground ALSO the 3 pin. The relay in the unit clicked, and pump started to suck! So apparently it is other way around. The 3rd pin should be grounded when suction is needed.

I installed the pump with test leads and tried to dry suck the system. Every component is holding vacuum. So my only problem is, where to put that wire from the brake vacuum switch. When looking those 240 diagrams, it is obvious that it should be connected to the brake light switch. But to which pin? Well I gamled and put it to the green yellow pin. Result, brake fuse blown out. Ok, I took the wire to the other pin, which now has 3 wires and replaced the fuse.

Go to test drive. Result, CC works! So Thank you all, problem is now sorted.

 

Hi, little bit off the subjects but do you have volvo 940 91 wiring diagrams? And even better if for D24TIC.
Thanks 👍