I've had a good search round the site and can't quite find the answer I want.
Hence....
First post so here we go (and its a bit long).
I'm having a spot of bother with the family bus and so I've had the laptop and fault code reader out to see what it says.
I've got a small number of fauly codes, namely P0312, P0378 and P0430.
I've looked these up on this site and I've decided to change the crank sensor and both (yes both) Lambda sensors.
This code reader also provides a number of monitor functions and I noted that the Timing advance would mostly be around the 14 to 18 degree mark but would periodically jump to -55 degrees. Hence I'm changing the sensor.
I was also suprised to see the O2 sensor (bank1) would stay mostly at around 0.8V (that is high, yes?) but would periodically jump instantaneously to 0.08V. The bank2 sensor stayed pretty solidly at 0.8V. Hence I'm changing both. Here's hoping my Cat isn't toast.
I should add that the symptoms of a problem were the occaisional shuddering idle as I pulled up at junctions. This would clear to a perfect idle after an engine stop and re-start. I should add that during the 20 minutes or so that I sat with the car idling on the drive and watching the monitors, it inexplicably just stopped 2 or 3 times, as though I had just switched it off, but hadn't. It re-started instantly. I have no engine check lights showing at all.
Most odd was the Intake Air Temperature sensor reading. The temperature monitored was 47 degrees C! Occaisionally this would jump to -22 C, but that was occaisionally. The coolant sensor was reading between 92 an 99 C (fan going on and off). The ambient temperature was 1.5 C. Decidedly chilly in fact.
My quesion is, what should the resistance value of this sensor be at around 0 C as it is at the moment. If I measure it with my meter, it reads 7.2 KOhms. If I google IAT, I can get two different types of IAT (general info not GM specific), one type (higher resistance) that is far more documented than the other (lower resistance). If I use the graphical info on the well documented type, I work out that my 7.2k sensor should indicate around 50 C, which is near enough to what the monitor was showing, but what I need to know, is this correct, or should I spend the (gold plated) £41 on this dealer only part and replace it?
My issue with this is that I noted that the sensor did respond to a temperature change (blowing warm air on it, its resistance fell). I also wonder if the monitor function of this device was just getting a Voltage reading back from the ECU, and just interpretting this Voltage by assuming the sensor was the higher resistance type to get the value that broadly corresponds with what I measure with my Ohm meter. Or, is it really a lower resistance type, and 7.2 kOhm is correct for this sensor. Does anyone know if the ECU actually presents a temperature value for the monitor to display?
Any advice Please?
By the way, I've recently had the head gasket and timing chain replaced as a) the head gasket had gone and the engine had consumed water (not into the oil, but the No. 1 cylinder) and b) the chain as the plastic guide at the front of the engine was found to be broken in half and fortunately had dropped safely into the bottom of the timing case (lucky break). The car has done 93k miles.
Cheers... Rob