Body Control System: Diagnosis Chevrolet Silverado 2500

Scan Tool Data Definitions

Battery Voltage: The scan tool displays the value of the battery voltage.

Ignition 1: The scan tool displays Active when the ignition switch is in the RUN or CRANK position.

Ignition 3: The scan tool displays Active when the ignition switch is in the RUN position only.

Ignition Power Mode: The scan tool displays the position of the ignition switch. The scan tool displays Off, Run, Crank and Unknown. The word Unknown is displayed when the BCM can not determine the position of the ignition switch.

Julian Date: The scan tool displays the date that the body control module (BCM) was manufactured.

Key in Ignition: The scan tool displays Yes when the ignition key is fully inserted into the ignition switch cylinder. The BCM uses this data to control the chime feature.

Module Part Number: The scan tool displays the part number assigned to the BCM that is currently in the vehicle.

Software Design Suffix: The scan tool displays the version of the software part number in the BCM.

Software Part Number: The scan tool displays the software identification number in the BCM.

Scheme 5

Circuit Description

The internal fault detection is handled inside the control module. No external circuits are involved.

Conditions for Running the DTC

The Microprocessor runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

Action Taken When the DTC Sets

The microprocessor refuses all additional inputs.

Conditions for Clearing the DTC

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

1. This DTC may be stored as a History DTC with out affecting the operation of the module. If stored only as a History DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a Current and History DTC, replace the module.

The internal fault detection is handled inside the control module. No external circuits are involved.

The module microprocessor must be active/awake.

Conditions for Setting the DTC

This DTC indicates the KAM in the module has been reset. It is a normal occurrence when battery positive voltage or ground is removed from the module, such as a battery disconnect.

The microprocessor revert back to the base programmed critical operating data until new data is learned and stored in KAM.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

As part of normal data processing, the module performs a data programming check on its writes to the electrically erasable read only memory (EEPROM). The EEPROM write error detection is handled inside the control module. No external circuits are involved.

The module runs the program to detect an EEPROM write error. The only requirements are battery positive voltage and ground. This program runs even if the battery positive voltage is out of the valid operating range.

The module writes information to a data block in the EEPROM. The module then reads the data and compares it to what was sent to the data block. If the data does not match after 3 consecutive attempts, the module sets the DTC.

The module writes to another area of the EEPROM, this becomes the new permanent area to store the data. The data location is allowed to change until all of the available EEPROM is used. If a B1004 DTC is also set, the module reverts to base operation values programmed for those blocks of data that have failed. The blocks of data that have not failed the checksum test are not affected.

1. A current DTC clear when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

The electrically erasable read only memory (EEPROM) check sum error detection is handled inside the control module. No external circuits are involved.

The module runs the program to detect an EEPROM checksum error after each wake-up. The only requirements are battery positive voltage and ground. This program runs even if the voltage is out of the valid operating range.

The module retains an inverse copy of the digital value stored in certain blocks of memory in the EEPROM. The module then reads the information from those certain blocks and adds the stored inverse value to the current value if they do not equal O, the module sets the DTC.

The module reverse to base operation values programed for those blocks of data that have failed the check sum test. The blocks of data that have not failed the check sum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

Scheme 6

Important: Review the system operation in order to familiarize yourself with the system functions. Refer to Body Control System Description & Operation

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the body control system. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175672-S27030348872005042500000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

See Power Mode Mismatch .

Normal vehicle class 2 communications and module operations will not begin until the system power mode has been identified. Discrete wires from the ignition switch contacts are monitored by the power mode master (PMM) module in order to determine the correct power mode. The PMM communicates the system power mode to all class 2 modules on the class 2 serial data line. Refer to Body Control System Description & Operation to identify which module is the PMM and the applicable power mode look up table.