How are you doing? Just bought a 2002 S40. Well already after about 2 weeks my check engine light is on. The code read "coolant temp below thermostat temp" has anyone had this problem? Any ideas on what the cause/repricussions of this might be? Is it something that needs to be fixed? If so how much or how hard will it be? Thanks for the help.

:puzzled: Is the temperature gauge working ie rising? If so I'd guess the thermostat is dodgy. If the wiring is loose or damaged it could also give weird readings. Best get the dealer you got it off to check if it's under warranty. If not, find and remove the thermostat and check for corrosion. They tend to rot nicely. also trace the wiring as far as you can to check for damage. failing that, get the ecu looked at. it may be a fault in the program. Best of luck.

Depending which S40 variant you have, the coolant temperature sensor is almost certainly located on the left-hand end of the cylinder head. If it's a turbo then it should be screwed directly into the thermostat housing instead.

Does the temperature gauge start out on cold & then rise to normal after a while? Does it ever read too hot?

Likelihood is that either the thermostat or the sensor is faulty - there are ways of testing both items DIY, but if the sensor price is reasonable then easiest thing would be to replace them as a pair anyway.

Fingers crossed.

BB
:57:

The temperature seems to rise perfectly... starts out cold then sits in the middle somewhere. It never reads to hot. I do have a turbo. And no it is not under warranty.

:blush: So you say the thermostat is screwed into the thermostat housing. I will try and find it. I have never worked on a turbo before but am willing to give it a try.

Thanks for the help.

Any added tips on changing out the thermostat/sensor would be great.

Nope, that's not what I said..... It's the coolant temperature sensor that is screwed into the (outside of the) thermostat housing on your turbo model.

After you've drained down the cooling system, you'll need to unscrew the plastic engine cover. If you can't find the thermostat housing, just follow the top hose from the radiator to the top of the engine - it connects directly to the thermostat housing.

If replacing the 'stat, always ensure clean mating surfaces and use a new gasket (check that the box the 'stat is supplied in includes a gasket). Don't overtighten the bolts when re-assembling - the thread strips very easily - torque them to 17 Nm / 13 lbf ft. If the new 'stat has a hole near one edge, this hole should be located uppermost, to allow any air in the system to vent out to avoid airlocks.

Hope this helps.

BB
:thumbsup:

Hi,

I think you should not harry to look for the problem in the thermostat, of course if your are sure 100%. So i thing first of all you should full fill your
coolant tank till normal level and next day in the morning to check it. If when you full filled it the light goes off everything is ok, but if in another day the light stays and the coolant level would be under MIN level, it means that your system is leaking off. But if everything with the coolant level is ok and the light stays on you just check what the guys has recomended you ( to my mind temperature sensor) and thats all.
I had the problem like this, but my coolant light wasn't burning and temperature on the panel was normal in half position. Only the coolant was missing. I have checked thermostat it was good. Then i found out that coolant liquid was leaking to the cilinder.
If the system is not leaking and the coolant is not missing, so check only sensor.
Good luck!!!

:thumbsup:

Darmat,

The coolant was low. I will try your idea before purchasing a new sensor.

Does the service engine light turn off automatically or do I need to have it reset? Hopefully it will turn off and I will not need the answer to this question.

Thanks for the help.

Mark

Hey,
I just purchased a 2000 S40 and have the same code come up (P0128).
Just drove it home from the volvo dealer.
They upgraded the car's computer software to Ver 2 and cleared the code and in less then 10 miles; it's on again.

Taking the car back this upcoming week. I'll post their findings..

Oh ... and I too found my coolent level was low, before i took it in.
The code did not reset it's self. Auto Zone has a free scan service to read the code, but they refused to reset it.
In searching the internet ; P0128 means the temp sensor ( located on the black radiator housing) or thermosat is at fault..

I had that happen last year and the garage changed the temp sensor. The light came on again and I was sent to the dealer and they checked the sensor and reset the light. The light came back again and I had already spent too much money on it without getting anywhere. A Volvo mechanic suggested changing the thermostat which he suspected was stuck in the open position. I changed the thermostat myself and the problem went away.
That was my experience and yours could be something like that if everything else checks out - such as wiring, connection and the sensor.

UPDATE
Just picked up my car about an hour ago, the volvo dealer replaced both the coolant temperature sensor and the thermostat. The Lincoln dealer I purchased the car from agreed to pickup the bill.
Time will tell if one of these was "it". Volvo warranteed this repair for 12 months and unlimited miles.

Sorry the invoice is being processed and sent to the Lincoln dealer, so I can't provide part numbers
nor pricing info.

Hey man,,
Ive had the same problem and actually I brought the car to the dealership a few times. Last week they told me that my ECM needed to be replaced (ECM = ECU) because of some soft of a recall which was causing the codes to be thrown and the light to come up. I'm still waiting for the part to come in, but I let you know i it went.
Meanwhile, after they replaced the thermostat and the sensor I'm sorry to inform you taht the light WILL come back on again, it's just a matter of time - it happened to me to. Just take it to the dealerer and ask them about the recall of the ECM.

Good luck

Hi, I am a newbee too.

I have the same problem with my Volvo S40. I've done a lot of research on the Internet and found this forum. Everywhere I've checked it said to replace both the thermostat and the sensor, so I'll try that. I'm going to get the sensor and the thermostat to see if that fixes it. I'll let you know what happens.

Good Luck,

Dave

guys visit www.s40concepts.net for all your answers... !!!!!!!!!!!!

Could someone please post a picture showing where the thermostat and temperature sensor are located (preferably on a 2002 S40), otherwise, I will post a pic and you guys point it out.
From what I see online, the thermostat is NOT the same as the cap that closes the coolant reservoir. I am referring to the black cap that is located as close as you can get to the passenger within the engine compartment (if you look at this pic, pic of 2001 S40 engine compartment , the cap is above the left side of the strut tower bar)

I changed the thermostat in mine and reset the light. It's been about 10,000 miles now and it never came back on. I think the computer is just really sensitive to the proper operating temperature. Thermostats are cheap and so easy to fix. As they wear they open sooner than they are supposed to. You wouldn't notice if it was a little less cooler than it's supposed to be just by looking at the gauge in the dash, it's not that accurate.

How do you reset the light after changing the sensor and thermostat?

I just got a 2002 S40 with the same code. Took it back (under warranty) and already had the temp sensor replaced. The light came back on the next day and it's back right now getting fixed. I'm not sure what they're doing but does replacing both the thermostat and sensor seem to fix the problem or will the light come back on?

Your S40 comes with 540 hp.

I have the same problem with my 2002 V40. I've replaced the sensor and thermostat. The check engine light remains off for about a week -- then it comes on again. Do I need to fix this? Why can't I just turn the light off? As I understand it, the light comes on whenever the car detects a problem, even if the problem is only momentary. If the light stays off for an entire week, doesn't that mean the problem isn't significant?