Can a faulty thermostat throw a Check-Engine light ??

[chrjen]

The heat suddenly disappeared in my v70 2,5t - at the same time the Check-engine lit up. Sounds like a faulty thermostat doesn't it ????

[p fandango]

no i don't think it can, the thermostat is purely a mechanical valve with no sensors

[Al115]

No, it can't - as the man said.

Read the codes and all will be revealed!

No heat at this time of year isn't good

[T5ER]

temp sensor gone faulty ????

[Dangerous Dave]

The heat suddenly disappeared in my v70 2,5t - at the same time the Check-engine lit up. Sounds like a faulty thermostat doesn't it ????

Is the heater cold, or do you mean the temp gauge reads cold? If its the temp gauge then the sensor would be faulty and throw a code

[nagrom]

I had a prob a couple of years ago on a V70r, car would hiccup and engine lamp came on, changed crank sensor, temp and cam sensor, no joy, changed thermostat, problem never reoccured, weird!

[chrjen]

I changed the thermostat today - and everything works as it should now. The check engine light has gone as well...

[Dangerous Dave]

Nice one matey, looks like the ecu noticed the drop in temp and flagged it.

[C70 GTT5]

[timbo_1975]

Yes it can. Reason being that the ECU is clever enough to notice that the engine is slow to warm up, or hasnt fully warmed up, when it thinks it should have. They are programmed to know that starting at water temp x with ambient temp y, the engine will take z mins to fully warm up. If this doesnt happen it will flag the CEL.

[LeeT5]

The heat suddenly disappeared in my v70 2,5t - at the same time the Check-engine lit up. Sounds like a faulty thermostat doesn't it ????

No! As above, thermostat is purely mechanical, no sensors. It's a Two stage stat' and therefore cannot be temporarily jammed open or removed to get you to the garage, don't try else you will sha.g the head.

Cheapest and easiest method here is to just replace the stat with a new one from Volvo. Don't muck about, just change it!! Then pray to god that you haven't cracked the head...you will know if you have cos with this engine the car will normally be misfiring quite badly.

A new engine is over a £1000 so take every precaution before you drive off into the sunset. Check absolutely everything before the car leaves your driveway...or get the car to a garage.

[LeeT5]

I had a prob a couple of years ago on a V70r, car would hiccup and engine lamp came on, changed crank sensor, temp and cam sensor, no joy, changed thermostat, problem never reoccured, weird!

Circumstancial...not related, Garanteed.

[LeeT5]

Yes it can. Reason being that the ECU is clever enough to notice that the engine is slow to warm up, or hasnt fully warmed up, when it thinks it should have. They are programmed to know that starting at water temp x with ambient temp y, the engine will take z mins to fully warm up. If this doesnt happen it will flag the CEL.

not if the car is started from cold and left idling for 30 minutes it won't. The ambient air temp will remain unchanged and the water temp will take a lot longer to get to 92 degrees. Therefore z mins will be massively increased compared to if you start and drive hard immediately. You won't get the Mil light on just because your warm up time has ended and your engine isn't warm enough!

[Dangerous Dave]

My thermostat was playin up recently, the engine took ages to get warm, would only reach 1/4 on the gauge, then eventually it would get to normal temp, new stat sorted it, but it never threw a code.

[Al115]

I've had a few fail and nope, no code.

[orse]

Only way i,v known the engine light to come on due to a thermostat failure is when its stuck shut and the engine overheated.The cylinder head temperature sensor brought on the engine light due to the thermostat failure.

[volvoturboman]

I had thermostat problems earlier in the summer as some of you will know, it seized shut. I removed it but never replaced it until recently, when the colder weather came along my engine management light came on. New thermostat and lights gone, apparently as said before it was because the car was not running at operating temp.

[Dacvolvo]

Hey Folks

I know this is an old thread, but I've only just read it. My gold C70 T5 suddenly threw up the engine management light after me having owned the car for a few months. At the same time, I also noticed that the engine temp gauge wasn't going to the half way mark as it should. Even thought the vents were kicking out hot air, the engine was reading as almost cold even after a 2 hour drive.

I bought a new thermostat, fitted it and everything including the engine management light went back to normal. So yeah, I'd state quite happily that a faulty thermostat will (for whatever reason) activate the management light.

[nagrom]

Circumstancial...not related, Garanteed.

au contraire, I don,t know how you can "guarantee" that it was circumstantial when the thermostat fixed the fault after trying pretty well every sensor on the engine including plugs, leads, dizzy cap, spark generator,ecu

[Pistol Pete]

I can also say my car when coming to work ona cold morning.. would throw up the ECu fault as it had not warmed up fully

found it had no thermostat in it.,..

now fitted.. never seen the fault light come up since..