I just was given a nice 2005 S40 non-Turbo model. The check engine light comes on, and a P0172 OBD-II code is registered. However, when I hook up an iCarSoft scanner, no DTC codes are recorded on the ECM. Other modules are recording DTCs for things like the doors, etc.

The MAF had been replaced just before we were given the car. The car was in the Volvo dealership, who could not find anything obviously wrong with it, but they didn't think it was worth their effort and $$ to do a deep dive into the sensors. The car runs beautifully.

Is it unusual for a generic code to get thrown without a corresponding Volvo-specific DTC code? Would this help diagnose what could be wrong? I am leaning towards performing a smoke test on the hoses as a first start.

 

Have you replaced the upper oxygen sensor yet? They are good for about 100k miles.

 

I will check on whether they have been replaced, since the car has 165,000 miles on it. I would have thought a bad sensor would throw a DTC code, though.

Are there specifications for what the sensor outputs should be, since I believe I can monitor the signals live with the iCarSoft scanner?