Diagnostic System Check

Diagnostic System Check (Part 1 Of 2):

Diagnostic System Check (Part 2 Of 2):

CIRCUIT DESCRIPTION
The Heater-A/C Control Diagnostic System Check is an organized approach to identify problems associated with the heater-A/C control. This check must be the starting point for any heater-A/C control complaint, and will direct you to the next logical step in diagnosing the complaint. The heater-A/C control is a very reliable component and is not likely the cause of the malfunction. Most system complaints are linked to faulty wiring and connectors, and occasionally to components. Understanding the computer system and using the tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.

DIAGNOSTIC AIDS
^ The following conditions may result in an intermittent operation of the heater-A/C control with no DTC stored:
- Any condition which results in the interruption of power to the heater-A/C control.
- Out of range battery or ignition voltage specification. Normal battery or ignition voltage: 9.0-16.0 volts.
- A loose or damaged ground(s).
- An open or shorted serial data line.
^ An intermittent failure in the electronic system may be very difficult to detect and accurately diagnose. The heater-A/C control tests for different malfunctions under different vehicle conditions. For this reason, a thorough test drive is often needed in order to repeat a fault condition. If the system malfunction is not repeated during the test drive, a good description of the complaint may be very useful in locating an intermittent fault condition. Faulty electrical connections or wiring cause most intermittent problems. When an intermittent condition is suspected, check the suspected circuits for the following conditions:
- Poor mating of connector halves or backed out terminals.
- Improperly formed or damaged terminals.
- Wire chafing.
- Poor wire-to-terminal connections.
- Dirty or corroded terminals.
- Damage to connector bodies.
^ Use the J 35616-A whenever a diagnostic procedure requires probing or checking a terminal. Using this adapter will ensure that no damage to the terminal will occur and will give an idea of whether contact tension is sufficient.
^ If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Perform a thorough inspection of all related wiring and connectors pertaining to the history DTC stored. Refer to Intermittent and Poor Connections. Intermittent and Poor Conditions
^ Exit all scan tool tests before cycling the ignition the OFF position to the ON position unless the scan tool instructions direct otherwise. Follow the operating instructions in the scan tool operator's manual. Failure to follow these instructions may set DTCs, cause vehicle system malfunctions, set false DTCs, or cause scan tool malfunctions.
^ Check all relative fuses for the heater-A/C control. If open, check the circuits which are fed power by these fuses for a short to ground.
^ Make sure all relative grounds see schematic are clean and tight.
^ Check for a broken or partially broken wire inside of the insulation which could cause system malfunction but prove GOOD in a continuity/voltage check with a system disconnected. These circuits may be intermittent or resistive when loaded, and if possible, should be checked by monitoring for a voltage drop with the system operational (under load).
^ Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems. Refer to General Troubleshooting Procedures. Diagnostic Aids

TEST DESCRIPTION
Numbers below refer to the step numbers on the diagnostic table.
1. This test determines if communication can be established with the heater-A/C control.
2. This test checks for stored heater-A/C control DTCs.
3. This test checks the heater-A/C control power circuits.
4. This test checks the heater-A/C control ground circuits.
7. This test checks for a driveablity problem.
8. This test checks for a problem with the blower controls.
9. This test checks for a problem with the A/C compressor.
10. This test checks for a problem with the rear defogger.
11. This test checks for a problem with the air flow.
12. This test checks for a problem with the LH air temperature control.
13. This test checks for a problem with the RH air temperature control.