Lately the C32 has felt unwell, compared to its usual beastly self. Sort of felt like maybe I wasn't getting boost. I hooked up my laptop this morning and ran AutoEnginuity to datalog some sensors during my drive to work, and sure enough the manifold pressure sensor value was fluctuating between about 0.8 and 1.25 (maximum value according to the software is 16.0). Among other things, I logged intake air temperature and coolant temperature. Intake air temperature never got above 80 degrees Fahrenheit, as I would expect without there being any boost pressure. Coolant temperature was a reading in Volts, and read 0 the entire 30-40 minute commute. From what I know, the sensor provides resistance, and the computer uses that to compute a voltage, so I assume that's what I'm seeing in the software. Lower voltages seem to correspond to higher temperatures, so I would think a voltage of 0 would have the computer thinking the system is overheating - but I have no warning indicators about that. If the system is smart enough to know that it isn't actually overheating, based on some additional input, then shouldn't it also know that the sensor isn't working properly and throw on the check engine light? I can certainly see how a faulty coolant temperature sensor could prevent the supercharger from clutching in, but I have no CEL, and no indication of any coolant temperature problems, and that's what is confusing me.

When I get home tonight I'm going to test the sensor output directly to see whether that contradicts what I've seen in the software. I'm not sure why it didn't occur to me to pull the coolant temperature reading from the computer in the dash this morning, but I didn't - I will do that as well to see what (if anything) it's reading. And now that I think of it - does the C32 have a separate temperature sensor for the "gauge" (even though there isn't really a gauge), or is there just the one?


Any advice is welcome.

 

Alright, part of the mystery is solved I think. I noticed that in the Enhanced Powertrain Module there are two coolant temperature sensor inputs to choose from, one reads in Volts and that one is always zero, all the time, in my car. The other is a reading in degrees Fahrenheit, and that one is giving sensible values - values that match what the computer in the dash show me (the little virtual gauge). Similarly, there are two different intake pressure values to choose from, one in un-specified units (apparently with a 0.0-16.0 range) and another in hPa. Of course, with the laptop hooked up on my way home she ran like a beast, supercharger whining away. I didn't push her hard enough to get full boost, but have 12.4psi recorded from a few occasions when I goosed her a little. So whatever is going on seems to be intermittent. And I guess that 0v coolant sensor signal is due to some sensor not present in my car but supported by ME2.8

 

Did you ever figure out what the cause was? I am having a similar issue with my C55. It has a intermittent P0456 (evap vacuum -very small leak), but I noticed that the coolant temperature is is indicating high. At cold start up it will climb up 135 degrees F. The dash temp gauge reads normal.