I'm hoping someone can provide guidance.

I bought a 2005 Volvo S40 about six months ago. I noticed within a few weeks that the ambient air temperature sensor is flakey. Most of the time it works OK, but every once in a while I start the car and it says -40'C. It will slowly work it's way back toward the real temperature as we're driving.

I've also noticed over the last few months the car seems to occasionally run a little rough at idle and lack power. It's hard to tell how much of this is in my head, and I don't have anything to quantify this with. There has never been anything on the dash that suggests a problem.

A few days ago the CEL came on. Before the day had even ended, it was back off again. While it was on, the car was still running fine, maybe even smoother than normal. So I bought a bluetooth ODB2 scanner and plugged it in to see what I could find. I found a saved code P0070. Doing some research that suggests a problem with the ambient air temperature sensor. That would make sense based on my observations.

I have the Haynes manual for the car, but it doesn't mention the ambient temperature sensor. It only refers to the intake Manifold absolute pressure/Intake air temperature sensor which seems to be a single unit. Is this the same thing?

How does one go about checking the temperature sensor? I have a multimeter and the knowledge to use it, but don't really know where to start.

Would an ambient temperature sensor cause the car to run differently? I would think the intake temperature/sensor would be used for fuelling, and the ambient was just for driver information.

 

It could be influencing the intake preheat flaps... but the ECU is aware of the sensor so its doing more than just the dash temperature... There are other posts that suggest the sensor is in the driver's door mirror (at least for the LHDs) where the door's wiring harness can fray and needs to be replaced or it can just be the sensor.

 

Thank for the reply. I've been doing some more reading and I guess this is a pretty common problem with these cars. I noticed yesterday that there is now a problem with the left side (passenger) door lock. It doesn't seem to be related to the temperature, since it's constant where as the temperature seems to be working fine now. When I use the keyless entry to lock or unlock the car, the left front door doesn't move with the rest. It will remain unlocked or locked unless you manually press the lock down or open the handle from the inside.

Looks like I'm going to be pulling the door apart next weekend. I'll have a look at the wiring harness while I'm in there.