cruise control triggers limp mode

Paul_okie · Post by **Paul_okie** » 08 Aug 2016, 08:42

2001 V70 XC.
I have reproduced/proved this string of events several times just to make sure I'm not missing something:
1) turn cruise control on
2) set cruise control
3) press + (accelerate button) on steering wheel
4) "Urgent Service Required" lights triggered, limp mode, 2k RPM max.
5) pull over, turn car off, restart - can then drive normally but urgent service required light is still on. The light will go off after a single rest/restart cycle and no other CEL / service lights remain.

Or, same steps as above but eliminate pressing the accelerate button...everything seems to work pretty well until the cruise is forced into accelerate function by a hill - and even then it's pretty spotty - doesn't always do it.

I can reproduce all the driving behavior above with no cruise control and never have a problem. So, I feel pretty confident that this is strictly a cruise control problem. Before I had narrowed this down to a cruise control issue an independent volvo mechanic did check the codes and print them out for me. The only thing of interest was a misfire in cylinder 5. Accordingly, I did change the oil filler cap which appeared to be leaking, and changed spark plugs. This made no difference on the cruise control issue.

I have also tried holding the brake pedal up with my foot to see if maybe it's a brake sensor. No dice there.

So, I'm thinking either a vacuum hose or possibly a relay? Anyone run into this before?

Post by **abscate** » 08 Aug 2016, 09:02

On your fly by wire car, the cruise control is implemented through the ETM - electronic throttle Module/body/system

Im going to guess either you have a short in the cruise control wires on the stalk, or a fault in the ETM.

How old is the ETM - how many miles on it?

Paul_okie · Post by **Paul_okie** » 08 Aug 2016, 09:05

not sure on the ETM - I recently bought the vehicle. However, it does have yellow sticker.

Post by **abscate** » 08 Aug 2016, 09:43

You would have to have megamiles on it to have gone through two ETMs, like >200k

If you can get a picture of it it has a date code.

I ***think*** both the gas pedal and cruise input acceleration demands to the ETM through the ECU, so Im confused as to how one can work and not the other - unless there is short in the cruise stalk. This system fails safe so any unexpected commands will put you into limp. I should say, your car into limp

Paul_okie · Post by **Paul_okie** » 08 Aug 2016, 12:06

ok - I'll see if I can get a good pic of the ETM date which will be good to know anyway. It'll probably be awhile before I attempt any cruise stalk wiring investigation. But I will post what I find back here as I've seen a few other threads along these lines with no final conclusion. Thanks for the help.

Paul_okie · Post by **Paul_okie** » 08 Sep 2016, 11:48

Haven't had time to investigate cruise control wiring, but after driving 90 miles on turnpike with 75mph speed limit (no cruise) I'm thinking it's not really the cruise that is causing the problem after all.

It drives 95% fine, but when holding steady speed under load (like going up a hill) there is a predictable distinctive hitch in the gait. If, instead of holding steady under load, I push the accelerator a bit and force a downshift then all's well - no skip.

Perhaps my problem is related to a transmission sensor or something like that where ECM calls for downshift but for whatever reason no downshift occurs?

I suspect the limp mode on cruise is triggered by this same skip.

Paul_okie · Post by **Paul_okie** » 16 Sep 2016, 10:44

ok - adding another piece to the puzzle here. Since it's cooling off a bit I noticed the car runs much smoother without the a/c on. Last night I was on the highway for 20 miles or so. I set the cruise at about 40mph and then hit the accelerate button on the steering wheel and made it up to speed limit (plus or minus). Normally, this would have produced a limp mode condition, but with no a/c everything was fine. I left it on cruise the rest of the way home - no prob.

So...a/c clutch issue? When accelerating the a/c should disengage to deliver more power to the wheels - perhaps this isn't happening correctly or smoothly enough which causes what feels like a "skip", which could cause the cruise to freak out and limp?

Post by **abscate** » 16 Sep 2016, 12:54

I doubt that is a load issue - it really sounds electrical in nature. I think there are some shared circuits with AC clutch and other stuff from previous threads.

Paul_okie · Post by **Paul_okie** » 01 Nov 2016, 22:24

Pretty sure I resolved this problem. I need to get it on the highway for a longer cruise control test and will then post final update I hope.

I noticed a few months ago that this car had the wrong battery, but I thought surely that couldn't cause my problems. Well, replaced battery with correct one. Quick test drive, a/c on, cruise on and hit accel button on steering wheel from about 40 to 60 mph. All good, no problem. Plus, it's idling much much better.

Side note. Courtesy lamps and sunroof had no power after reconnecting battery. Quick search here turned up a thread that led me to lock/unlock 3 times with key in driver door which made everything work again.

Post by **abscate** » 02 Nov 2016, 03:43

Probably not the battery that fixed it by type, but if the voltage was low on a CANBUS car that will cause all sorts OFC wierdness