A Diagnostic System Check - Body Control System

Circuit Description

IMPORTANT:
- After performing a repair that requires clearing DTC(s) from the BCM, inspect the repair by operating the vehicle within the limits shown in Conditions for Setting the DTC. Operating the vehicle under these specifications will verily that the repair was completed properly.
- Use the J 35616-A when probing electrical circuits in order to prevent damage to damage to electrical components and connectors. The J 35616-A is the ONLY recommended method of probing connectors, terminals, fuse blocks and relay blocks. The J 35616-A contains an assortment of flexible connectors used in order to probe connectors, terminals, fuse blocks and relay blocks during diagnosis.
- Do not use a test lamp in order to diagnose the BCM electrical systems unless you are specifically instructed by diagnostic procedures. Use the J 35616-A when diagnostic procedures require probing of connectors. Refer to Special Tools.
Tools and Equipment

- The Body control module (BCM) will withstand normal current draws associated with the vehicle operations. Do not overload any circuit.
- When you test for opens or shorts, do not ground or apply voltage to the BCM circuits unless instructed to do so. Use a J 39200 digital multimeter (DMM) (or equivalent) in order to test these circuits. Test electrical circuits using a DMM while the BCM connectors remain connected to the BCM or to the recommended breakout box.
- Do not remove or apply the voltage to the BCM when the key is in the RUN position. Always turn the key to the LOCK position when any of the following components are removed or connected:
- Battery cables
- Fuses
- Connectors
- Whenever a BCM removal or replacement procedure is performed follow the instructions. Use the following guidelines when servicing the BCM system:
- Always DISCONNECT the BCM connector (BRN) FIRST.
- Always CONNECT the BCM connector (BRN) LAST.
- The BCM may set codes when the ignition switch is in the OFF position. When you disconnect the electrical connectors from the BCM, the DTCs will set. The BCM may require 20 minutes (1216 seconds) in order to power down after the following conditions exist:
- The ignition switch is turned to the OFF position.
- The BCM is not receiving any active inputs.
- The BCM does not receive any active inputs for 20 minutes.

The Body control module (BCM) diagnostic system check is a test that identifies a malfunction in the electronic system. The BCM diagnostic system check is the starting point for any BCM complaint. Understand and use the BCM diagnostic system check table in order to reduce diagnostic time and prevent unneeded replacement of components.

Step 1:

Steps 2 - 6:

Steps 7 - 10:

Steps 11 - 14:

Steps 15 - 18:

Test Description
The numbers below refer to the step numbers on the diagnostic table.
1. This step determines if the scan tool may be powered up by the data link connector.
2. Most of the diagnostic procedures require a scan tool. Serial data must be available. This step verifies that communication may be established with the BCM.
3. This step tests for any diagnostic trouble codes (DTCs) that are stored in the BCM. If the scan tool is able to read the DTCs, the serial data line is OK.
4. This step tests for Class 2 communications with other systems. If the scan tool is able to read the data, the Class 2 serial data line is OK.
5. This step inspects the TBC fuse. The TBC fuse is located in the underhood fuse block.
6. This step determines if the underhood fuse block is supplying voltage to the TBC fuse.
7. This step determines if the BCM power CKT 1140 is open between the BCM and the TBC fuse.
8. This step determines if the BCM ground CKT 1850 is open.
12. This step determines if the following components are good. The no-start condition indicates that the malfunction may relate to Passlock (TM) or engine controls:
- The BCM power and ground circuits
- The BCM
14. This step determines if the BCM power CKT 39 is open between the BCM and the GAUGES fuse.
16. This step determines if the BCM power CKT-41 is open between the BCM and the CRUISE fuse.