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Old 09-17-2017, 02:54 PM   #1
DavidSamuels
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Default 850 Cruise Failure

Looking for an epiphany. Our '97 855 has lost it's cruise control. This happened when a rebuilt alternator's regulator failed and was overcharging. May be a coincidence, don't know. Once the alternator was repaired, the cruise no longer worked. I had been experiencing, for about a year, a situation where the cruise was slow to accelerate the car via the stalk button. It worked but was sluggish. Other than that, it was fine. In troubleshooting the failure, I found the pedal switch had one broken clip and was sitting at an angle. Hard to say if that was the sluggishness issue, but replaced the switch and I adjusted the plunger to the depressed pedal (running) by pulling it out per instructions and letting it self-adjust. The pump is tested good. Plumbing is good and the MityVac at the pump will pull the diaphragm all the way in. Have swapped the ECU for another. Pulled the column cover and confirmed there are no broken wires in that little bundle. No codes at all. Odometer and speedo working correctly, so I'm assuming the speed sensor on the trans is okay. What am I missing? Any help appreciated. Haven't found a good article to diagnose perhaps via the terminals of the cruise ECU. DS
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Old 09-17-2017, 03:01 PM   #2
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vacuum leak

the brake pedal switch goes bad - I had a hard time adjusting my used one.. got another and it forked
the line in the engine compartment rubs through
the rubber cheese elbows that hold the vacuum line go out


ps I had the same issues as you did and found a vacuum leak where I didnt look before, then the switch went bad about 2 months later
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Old 09-17-2017, 04:28 PM   #3
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Thanks Jack. Switch is factory brand new and I can pull a vacuum from all the way forward at the pump to the diaphragm and it's perfect. Holds vacuum and the pedal gets pulled all the way in. Gotta be something in the electrical/control setup.
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Old 09-17-2017, 04:39 PM   #4
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I would try to get my hands on the documents from the factory and go diagnose the circuit.

A high level scan tool might reveal a code that could help. Or doesn't the 97 still have the blinky box too?
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Old 09-17-2017, 04:42 PM   #5
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Originally Posted by DavidSamuels View Post
Thanks Jack. Switch is factory brand new and I can pull a vacuum from all the way forward at the pump to the diaphragm and it's perfect. Holds vacuum and the pedal gets pulled all the way in. Gotta be something in the electrical/control setup.
Im trying to think of what was wrong with mine.. it was something stupid simple one time

check 1 and 17?

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Old 09-17-2017, 04:45 PM   #6
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I would try to get my hands on the documents from the factory and go diagnose the circuit.

A high level scan tool might reveal a code that could help. Or doesn't the 97 still have the blinky box too?
only an oscilloscope works on the cruise control

97s do not have the diag boxes ... obd2 bro
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Old 09-17-2017, 04:54 PM   #7
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^^^ This. One instance where I wish the blinky box was still here. Jack, Everything vacuum related is working. Pump pulls strong on the bench and will pull the diaphragm in if I jump power to it in the car. Wondering if the stalk switch is bad, but they don't seem to be problematic from what I've read. Thanks.
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Old 09-17-2017, 04:55 PM   #8
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fuk


yes that also went bad on mine .....

sounds like you had two issues
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Old 09-17-2017, 05:01 PM   #9
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Follow this factory repair manual.

http://www.volvotips.com/index.php/8...ruise-control/
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Old 09-17-2017, 05:12 PM   #10
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^^^Well without a diagnostic box for '97, most of it is not applicable, but there are some tests at the ECU base/plug I can try.

I see that Vol FCR has a cruise option. It's instructions on how to hook up an LED and push button to simulate the pre-97 blinky box. Guess it's not accessible via the OBD2 port. Ugh.
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Old 09-17-2017, 11:40 PM   #11
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Originally Posted by DavidSamuels View Post
^^^Well without a diagnostic box for '97, most of it is not applicable, but there are some tests at the ECU base/plug I can try.

I see that Vol FCR has a cruise option. It's instructions on how to hook up an LED and push button to simulate the pre-97 blinky box. Guess it's not accessible via the OBD2 port. Ugh.
There is a test procedure to jump the cruise control and see where the broken link is.
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Old 09-18-2017, 08:59 AM   #12
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^^^^ Details??? Do you mean to manually activate the vacuum system for testing? Or more? Thanks.
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Old 09-18-2017, 02:57 PM   #13
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^^^^ Details??? Do you mean to manually activate the vacuum system for testing? Or more? Thanks.
Look under VACUUM SYSTEM CHECK in the repair manual.
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Old 09-18-2017, 03:35 PM   #14
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With a bidirectional scan tool, the right one such as VIDA, one could probably go in there and look at the data and maybe control the servo.

And a scope could be used to confirm a speed signal into the cruise control unit to verify the speedo is sending a signal out, son.
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Old 09-18-2017, 03:46 PM   #15
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When I swapped my 850 to a manual, I had to replace/add a relay to get the cruise to work. Not sure if yours could have gone bad with what you say happened but here is the relay number: 1378076

Might be worthwhile to replace it. They're $15.
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Old 09-18-2017, 04:44 PM   #16
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Originally Posted by matt b View Post
When I swapped my 850 to a manual, I had to replace/add a relay to get the cruise to work. Not sure if yours could have gone bad with what you say happened but here is the relay number: 1378076

Might be worthwhile to replace it. They're $15.
Not really needed a second relay. A tab on the stock relay needed to be cut off to make the CC work on a manual swapped 850.
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Old 09-18-2017, 05:16 PM   #17
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Interesting! Regardless, this is an automatic, and it was working before the alternator incident. Frustrating.
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Old 09-18-2017, 09:48 PM   #18
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Harry is right, you can cut or bend over a pin on the stock module to make it work in a manual, BTDT.

Zach...no OBD connection to the cruise on Dave's car, unless you have a VST, which aren't easy/cheap to come by. Aftermarket stuff won't touch it, newer stuff won't touch it.
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Old 09-19-2017, 09:06 AM   #19
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Guess it's time for a JY run, see if I can snag an ABS module (and hope it's been fixed) and a stalk. Jumping the pump at the socket proved the wiring to the pump is good. Creating the button and LED setup will be a last resort.
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Old 09-19-2017, 10:57 AM   #20
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And if the one you grab is bad, send it off to get repaired. It's a fairly straight forward fix, there are write ups floating out there.
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Old 09-19-2017, 11:30 AM   #21
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You could also exchange your existing module with one from Midwest ABS, ~$80 isn't a bad price to pay for a known good part and you're up and running the same day. Not sure I'd wanna mess with the junkyard lotto on a part that's pretty much guaranteed to fail.
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Old 09-19-2017, 11:38 AM   #22
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All you can do is verify power, ground, and signal at the module and figure out which is missing.

Furthermore, I have been becoming more of a fan of using test lights and noid lights to verify proper CURRENT to a circuit. I got nailed recently on a window regulator where it had 12v going to the motor, but after a switch, and a regulator install it still didn't work. Using a noid light we realized there wasn't enough current, but it would show up as 12v on a meter. It turned out to be a poor connection at a connector!
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Old 09-19-2017, 02:45 PM   #23
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Which means figure out a way to check for a VSS to the cruise module while driving since that comes from the ABS module, and make sure there's no missing pulses.
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Old 09-19-2017, 03:11 PM   #24
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Ah...now there's a piece of information I've been looking for. The trans speed sensor does not provide the pulse to the cruise? There was one post on the interweb about the cruise signal coming from the cluster, which means it would be from the trans. Thanks Gary. More support for the ABS fault. Also, now that I think about it, there have been a couple of instances in the last few months when the pedal gave an unusual pulse.
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Old 09-19-2017, 04:25 PM   #25
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Wiring diagram!

Then look up what kind of signal it is and find a way to measure it whether it be a AC voltage test on a meter, LED test light should blink, or graph it. I have my $80 Hantek scope in the electrical drawer to hook up to the laptop if I really wanted to graph something like a speed signal.

It would be a shame to put an expensive part in like a computer and have it NOT be the problem.

Another way would be with a factory level or equivalent aftermarket scan tool. One could go into the data parameters of the different modules and see if there is something like a valid speed data PID. And if the module is communicating, obviously there is power and ground to it! And of course, look for DTCs and do research as to what commonly causes the code. That is step one when I get a problem: pull codes, look for bulletins and research common points of failure.

Last edited by ZVOLV; 09-19-2017 at 04:36 PM..
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