Circuit Description
The BCM Diagnostic Check is an organized approach to identify problems associated with the BCM. This check must be the starting point for any BCM complaint, and will direct you to the next logical step in diagnosing the complaint. The BCM is a very reliable component and is not likely the cause of the malfunction. Most system complaints are linked to faulty wiring and connectors, and occasionally to components. Understanding the computer system and using the tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.
Diagnostic Aids
| • | The following conditions may result in an intermittent operation of the BCM with no DTC stored: |
| - | Any condition which results in the interruption of power to the BCM |
| - | Out of range battery or ignition voltage |
Specification
Normal BCM operating voltage: 9.0-16.0 V
| - | A loose or damaged ground(s) |
| - | An open or shorted serial data line |
| • | An intermittent failure in the electronic system may be very difficult to detect and to accurately diagnose. The BCM test for different malfunctions under different vehicle conditions. For this reason, a thorough test drive is often needed in order to repeat a malfunction. If the system malfunction is not repeated during the test drive, a good description of the complaint may be very useful in locating an intermittent malfunction. Faulty electrical connections or wiring causes most intermittent problems. When an intermittent condition is suspected, check the suspected circuits for the following conditions: |
| - | Poor mating of connector halves or backed out terminals |
| - | Improperly formed or damaged terminals |
| - | Wire chafing |
| - | Poor wire to terminal connections |
| - | Dirty or corroded terminals |
| - | Damage to connector bodies |
| • | If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Perform a thorough inspection of all related wiring and connectors pertaining to the history DTC stored. Refer to Intermittents and Poor Connections . |
| • | Exit all scan tool tests before cycling the ignition OFF to ON unless the scan tool instructions direct otherwise. Follow the operating instructions in the scan tool operator's manual. Failure to follow these instruction may set DTCs, cause vehicle system malfunctions, set false DTCs, or cause scan tool malfunctions. |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
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This test determines if communications can be established with the BCM.
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This test checks for communication DTCs stored in the BCM (communication DTCs begin with the letter U). Communication DTCs must be diagnosed and corrected first before diagnosing any other DTCs.
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This test checks for stored BCM DTCs.
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This test checks for an open in the BCM ignition circuit. The BCM receives ignition switch position status directly from the ignition switch and sends this information on the serial data line to other systems.
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This test checks for an open in the BCM ignition circuit. The BCM receives ignition switch position status directly from the ignition switch and sends this information on the serial data line to other systems.
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This test checks for an open in the BCM ignition circuit. The BCM receives ignition switch position status directly from the ignition switch and sends this information on the serial data line to other systems.
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This test determines whether communications can be established with other systems connected to the same serial data line.
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This test checks for any open BCM power fuses.
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This test checks the BCM power circuit. If the test light does not turn ON, there is an open in the BCM power circuit.
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This test checks the BCM ground circuit. If the test light does not turn ON, there is an open in the BCM ground circuit.
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This test determines if an open is present in the serial data line between the BCM and the DLC (CKT 1037).
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Does the scan tool communicate with the BCM? | -- | |||
Are any communication DTCs stored? | -- | |||
Check for any BCM DTCs. Refer to Diagnostic Trouble Code (DTC) List/Type . Are any of these DTCs stored? | -- | Go to Applicable DTC Table | ||
Does the scan tool display RUN? | -- | |||
Turn the ignition to the START position. Does the scan tool display CRANK for current power mode? | -- | |||
Does the scan tool display RETAINED POWER for current power? | -- | System OK | ||
Attempt to establish communications with the other systems connected to the same serial data line (PCM, RFA, IPC, etc.). Does the scan tool communicate with any other system? | -- | |||
Does the test light turn ON in all circuits? | -- | |||
Does the test light turn ON in all circuits? | -- | |||
With a test light connected to B+, probe all BCM ground circuits. Refer to Body Control System Schematics . Does the test light turn ON in all circuits? | -- | |||
Check for continuity between the BCM connector terminal (harness side) B6 and DLC terminal 2. Is there continuity? | -- | |||
12 |
Is the replacement complete? | -- | -- | |
13 |
Is the circuit repair complete? | -- | -- | |
14 | Locate and repair the open in CKT 1037. Is the repair complete? | -- | -- | |
15 | Locate and repair the open in the BCM power circuit. Is the repair complete? | -- | -- | |
16 | Locate and repair the open in the BCM ground circuit. Is the repair complete? | -- | -- | |
17 |
Is the repair complete? | -- | System OK | -- |
