'95 850 Cruise Control points of failure?

[marginal]

Thanks a lot MadeInJapan.
I already did check it out, but as lazy as I am, I didn't go in details, but I will have to, anyhow ...

[mishagos]

There's a cruise control light? Mine has never gone on! My cruise has been acting funny lately -- only catching at about 60mph, no matter what I set it at. Suggestions?

Ian

[Ozark Lee]

On an 850 there is no indicator light, it just kinda works or it doesn't. It appears you are new to the thread, what year is your car? The problems are the same but the diagnostics are different.

...Lee

[marginal]

I wonder what could be the problem with mine.
The symptoms are as follows:
1. When I activate it it takes about 1-2 seconds to start (which I believe is too long).
2. It does not control the speed evenly, often slowing down and then accelerating again.
3. Just a very light touch on the break pedal stops it (I'm not sure this is not OK though).
Could this be a leak in the vacuum system?
BTW I checked the the vacuum hose attached to the cruise pump under the battery tray, and it is OK.

Thanks for the help.

Well, it seems the problem comes from a faulty ABS module.
I wrote to a repair shop on eBay, and after they read what are the symptoms, they said it is the faulty ABS module which is responsible for the cruise control problems.

[RSM-GA]

Are the symptoms, diagnosis, and schematics the same on the S70 (98) as the 850's for the cruise system?

thanks

[chadeboy19]

My cruise control also does not work and my shiftlock only works occasionally. I'm wondering if these two problems could be related due to a brake pedal fault. I have a '95 850 as well and the cruise control has never worked for the nine months that I've had it. The shiftlock fault has also been occuring since I bought it.

[MNCO1]

My cruise was working then it wasn't. Used the advice from a couple of folks here and checked the simplest thing first. There it was. Vacuum elbow was just under and slightly in front of battery tray. Just reach in and replace. Cruise works again!

[larrybum]

I had an erratic cruise control....sometimes it would work. Sometimes, it just ignored my requests to set speed. When I first got the car a few years ago, I was having this problem. I replaced the control module on the firewall with one from a seller on EBAY, so it was used. Cruise worked fine up until a few months ago and the engagement became erratic again.

It seemed to be related to temperature, but the symptom was: once it would engage it seemed to work just fine. If I had to hit the brake or disengage it, it was a tossup as to whether it would engage again or not. i suspected the control module again and I began to wonder what could cause such erratic behavior. I have an electronic background and knew that cold solder joints could be a real problem with electronic items. I took the cover off the module to look at what was inside. I noted that, even though the car had been sitting for over an hour, the control module was very warm as if a lot of heat is generated there.

When I removed the cover, I found two soldered connections under the relay on the circuit board that looked suspect. When a component on a circuit board generates a lot of heat, it causes expansion, then contraction when it cools. Those heat/cool cycles can then caused a tiny crack to develop around the lead from the hot item at the solder joint on the circuit board.

There were two connections from the two main leads from the relay that had to be resoldered in order to clear up the solder crack I found. Once I did that and plugged the unit back in, I never say the problem again. IT looks llike VOLVO missed this problem in designing this module. Too much heat was being generated to prevent the solder connection from eventually failing.

A simple fix, but a complicated route to finding the problem. I'm sure many other things can affect cruise control operation, but add this one to the list of possibilities. No doubt other models of VOLVO use this module or one designed in a similar way.

[turbozutek]

Mine failed in a totally different way - the pump unit itself died.

The symptoms were the system would be lazy to engage, very slow to make speed corrections and sometimes just wouldn't activate at all. On occasion the system would be set at say 70mph, cut in at 63, speed up to 75 then down to 70 then slip to 63 and then repeat the cycle. Just perfect for motorway conditions!

I autopsied the pump and discovered that the top silicon seal (oval o-ring that lives just under the lid) is quite nasty and had failed, allowing water to corrode the motor unit. These pumps have a solenoid to purge the vacuum and when it does, a tiny amount of damp air is drawn in from the engine bay - and then directly over the motor which is inside the vacuum airflow (not such a great design that I don't think). Eventually, even with everything else being good, the pump will die!

The pump can be tested by applying 12v + to the pin nearest the front of the pump and negative to the middle pin. The pump should then run, you can test the pressure by hooking up a syringe with a length of tube to the suction pipe: it should pull the syringe in almost instantly and with good strength. If you can defeat it with your hand, it's not strong enough!

Switch the + to the pin nearest the back to engage the solenoid (should click for you)

Anyway, I installed a new pump and everything was fine after that; good speed regulation and near instant engagement.

Chris...

[rspi]

My cruise has been acting up and now does not work at all. Where is this "Control Module" at the fire wall? I thought the cruise control unit was under the battery trey? If someone has a pic that would be great.