SMU - Revised DTC P0540
| Subject: | Revised DTC P0540 |
| Models: | 2001-2002 Chevrolet Silverado Pickup Models |
| 2001-2002 GMC Sierra Pickup Models |
| with 6.6L Engine (VIN 1 - RPO LB7) |
This bulletin is being issued to revise DTC P0540 in the Engine Controls - 6.6L sub-section of the Service Manual. Please replace the current information in the Service Manual with the following information.
The following information has been updated within SI. If you are using a paper version of this Service Manual, please make a reference to this bulletin on the affected page.
The diagnostic information and procedures for DTC P0540 have been revised in the above applications to reflect the use of a scan tool to operate the intake air heater (IAH) during the testing procedure. The operation of the IAH depends on variables that may not be within the technicians control. By using a scan tool to turn the IAH ON and OFF, you can consistently put the IAH in the mode desired for that step in the test.
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. If the ECM detects voltage on the IAH circuit when the relay is commanded OFF, or incorrect voltage when the relay is commanded ON, a DTC 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, engine OFF for more than 3 seconds. |
Conditions for Setting the DTC
The heater line voltage is more than 8.1 volts with the relay OFF.
OR
The heater line voltage is between 3.8-8.1 volts with the ignition OFF.
AND
The heater line voltage is less than 0.5 volt below battery voltage with the ignition ON.
OR
The heater line voltage is less than 3.8 volts with the relay OFF.
AND
The reference line voltage is low with the relay OFF.
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. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls |
2 | Is DTC P0380 also set? | -- | Go to DTC P0380 | Go to Step 3 |
3 |
Does the scan tool display a voltage near the first specified value with the IAH commanded ON and near the second specified value with the IAH commanded OFF? | 11-13 V, 0.0 V | Go to Step 9 | Go to Step 4 |
Does the test lamp illuminate with the IAH commanded ON, and turn OFF with the IAH commanded OFF? | -- | Go to Step 9 | Go to Step 5 | |
5 |
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 10 |
6 |
Does the test lamp illuminate with the IAH commanded ON, and turn OFF with the IAH commanded OFF? | -- | Go to Step 11 | Go to Step 7 |
7 |
Does the voltage measure less than the specified value? | 1 V | Go to Step 8 | Go to Step 13 |
8 | Test the IAH control circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 |
9 | Test for an open or short to ground on one of IAH supply voltage circuits between the IAH supply stud and the ECM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 |
10 | Repair the open or short to ground in the IAH ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
11 | Test for poor connections at the IAH relay. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 |
12 | Replace the intake air heater relay. Refer to Intake Air Heater (IAH) Relay Replacement. Did you complete the replacement? | -- | Go to Step 16 | -- |
13 | Repair the short to voltage on the relay control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
14 | Test for poor connections at the ECM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15 |
15 | Replace the ECM. Refer to Engine Control Module (ECM) Replacement. Did you complete the replacement | -- | Go to Step 16 | -- |
16 |
Does the DTC run and pass? | -- | Go to Step 17 | Go to Step 2 |
17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK |
