Circuit Description
The HVAC control module communicates with the auxiliary HVAC control module through the HVAC control module data signal and HVAC control module clock signal circuits. This communication link is only used by the HVAC control module and the auxiliary HVAC control module to exchange HVAC data.
Conditions for Running the DTC
The ignition is turned ON.
Conditions for Setting the DTC
There is a loss of communications between the HVAC control module and the auxiliary HVAC control module.
Action Taken When the DTC Sets
The auxiliary HVAC control module will lose all automatic control.
Conditions for Clearing the DTC
| • | The DTC will become history if the HVAC control module no longer detects a failure. |
| • | The history DTC will clear after 50 fault free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that the HVAC control module data signal circuit is functioning.
-
This test verifies that the HVAC control module clock signal circuit is operating at the correct frequency.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
2 | Test the HVAC control module data signal circuit for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 3 |
3 | Test the HVAC control module data signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 4 |
4 | Test the HVAC control module clock signal circuit for a short to voltage, a short to ground, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 5 |
Measure the voltage from the HVAC control module data signal circuit to a good ground. Does the voltage measure near the specified value? | 1 Vdc | Go to Step 6 | Go to Step 7 | |
Measure the frequency from the HVAC control module clock signal circuit to a good ground. Does the frequency measure near the specified value? | 1.3 kHz | Go to Step 8 | Go to Step 7 | |
7 | Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the auxiliary HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the HVAC control module. Refer to HVAC Control Module Replacement . Did you complete the repair? | -- | Go to Step 11 | -- |
10 | Replace the auxiliary HVAC control module. Refer to Auxiliary Heater and Air Conditioning Control Module Replacement . Did you complete the repair? | -- | Go to Step 11 | -- |
11 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
