Circuit Description
The engine control module (ECM) uses an intake air heater (IAH) to warm the incoming air for proper cylinder combustion. The ECM grounds the control coil of the IAH relay to energize the heater during cold operation. The ECM sends a bias voltage on diagnostic circuits 1 and 2. If this voltage is not pulled low when the relay is OFF, or is not high with the relay ON, DTC P0543 will set.
Conditions for Running the DTC
| • | The battery voltage is between 10-18 volts. |
| • | The intake air temperature (IAT) is less than 23°C (73°F) with the engine running. |
| OR |
| • | The coolant temperature is less than 49°C (121°F) with the ignition ON, and with the engine OFF for more than 3 seconds. |
Conditions for Setting the DTC
| • | The IAH line voltage is between 3.8-8.1 volts with the IAH relay OFF. |
| • | The IAH line voltage is less than 0.5 volt below battery voltage with the IAH relay ON. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 | Is DTC P0380 set? | -- | Go to DTC P0380 | Go to Step 3 |
3 |
Does the scan tool display a voltage within first specified value with the IAH command ON and near the second specified value with the IAH command OFF? | 11-13 V, 0.0 V | Go to Step 4 | Go to DTC P0540 |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 6 |
5 | Repair the open in the IAH supply voltage circuit between the IAH Relay and the IAH. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 7 | -- |
6 | Replace the intake air heater. Refer to Intake Air Heater Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- |
7 |
Does the DTC run and pass? | -- | Go to Step 8 | Go to Step 2 |
8 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
