Engine Controls - Revised DTC P0540 Diagnostics
File In Section: 06 - Engine/Propulsion SystemBulletin No.: 02-06-04-048
Date: September, 2002
SERVICE MANUAL UPDATE
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 shown refers to the step number on the diagnostic table.
4. This step checks for battery voltage output from the AH relay to the IAH.
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