Car question

[xoxoxoBruce]

Code readers are wonderful, tells you what system the problem is probably in, although sometimes there's some overlap. However that's not the same a fixing it. OK here's one I've had, P0442 OBD-II Trouble Code. my code reader told me the code p0442 was the reason the check engine light was on, cool. By the way, p0442 is not exclusive to GM.

p0442 - Evaporative Emission Control System Leak Detected (small leak)
The vehicle's PCM (powertrain control module) tests the evaporative emissions (EVAP) system for large and small leaks among other conditions. In the case of this DTC, it indicates a fuel vapor leak in the EVAP control system. It means a very small leak has been detected. In fact, the leak can be from a hole as small as 0.04" in diameter. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system.

OK, find the leak and fix it, that should be simple, no electronical wizardry or anything. Where should I look?

A code P0442 most likely means one or more of the following has happened:
•A loose or improperly affixed gas cap
•A non-conforming gas cap (i.e. not factory/original brand)
•A small leak/hole in a fuel vapor hose/tube
•Other small leak in EVAP system
•Faulty vent o-ring seal
•Defective vent valve
•Defective purge valve
•Defective leak detection pump

Hmm, I can check if the gas cap is tight, but won't know if it faulty. Maybe if I light a match by the gas cap. No, bad move.
Leak in the vapor hose/tube. Well the hose goes from two spots on the tank, up to the engine bay vapor canister. A 0.04" hole, huh?

There's a vent valve and purge valve, one's on the top of the gas tank, between the tank and the body and the other is under the hood in one of the hoses. Wonder which is which, my reader only tells me p0442, and the repair manual says hook it up to the dealer's big buck diagnostic computer. Hmm.

In my case it turned out to be the purge valve that's easy to get at, but no way of knowing whether it's bad or not by looking at it.

Well how about a U1255 OBD Trouble Code?

U1255 - GM
Type Network - Manufacturer Controlled DTC - Manufacturer Controlled

Description Class 2 Communications Malfunction

Cause ECM DTC B with Freeze Frame and Failure Records stored or TOM DTC TCM flashes Sport Mode Indicator, TCM sends a MIL request to the ECM, the ECM illuminates the MIL, TCS is disabled and the TC Indicator is illuminated

Got it? Got it. Good.