You may be lucky enough to have no computer involved with your heater. In that case you diagnose it the same way we have for decades. If you DO have computer controls, your best bet is to get a copy of the manufacturer's service manual for instructions on how to access that computer's diagnostic tests and how to do the test for each code. Don't waste your money on Haynes or Chilton's manuals for things like this.
You can buy a subscription to an online version of a service manual too. One place to go is the top of this page, point to "Repair and Service", then click on "Manuals". You may find with the manufacturer's paper version, you'll be referred to separate diagnostic manuals for the individual systems, like anti-lock brakes, air bags, and AC / heater systems. Those supplemental manuals are usually included in the subscription services.
Also be aware that you're expecting the wrong thing from your mechanic and those fault codes. Diagnostic fault codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis, or, in the case of Engine Computers, the unacceptable operating condition. When a part is referenced in a code, it is actually the cause of that code only about half of the time. First you have to rule out wiring and connector problems, and if it's sensor-related, mechanical problems with that sensor. This is why the diagnostic time you're charged for includes way more than just reading the codes. Reading the fault codes is to your car the equivalent as saying to your doctor, "I'm in pain". It's just the starting point of the diagnostic steps.
Thursday, June 4th, 2015 AT 5:45 PM