The next step is to check the power supplies and grounds at the controller's connector. Best is to use a test light. If you use a digital voltmeter, the module should be connected to get more accurate readings.
Terminal 2 is a purple wire and must have 12 volts all the time.
Terminal 16 is a purple / orange wire and must have 12 volts when the ignition switch is on.
To check the ground wire, move the test light's ground clip to a positive source. The easiest to find is the battery's positive cable. Now, the test light will light up when you probe a good ground.
Terminal 3 is a black wire. That is the only ground wire. The test light must light up brightly when this wire is probed and its ground clip is on the battery's positive cable.
If these three wires are okay, that leaves the two data buss wires, and you need a scanner to see if they are related to the problem. You'd have more problems than just the HVAC Controller if the data buss had a problem, but with the scanner, you can see if the HVAC Controller is communicating with the other computers.
Wednesday, October 12th, 2016 AT 5:44 PM