Circuit Description
The body control module (BCM) internally grounds the door unlock relay control circuit for the rear door unlock relay when it receives a class 2 message from the driver door module (DDM), passenger door module (PDM), or the liftgate module (LGM) with a keyless entry transmission. When the BCM grounds the door unlock relay control circuit, the rear door unlock relay is energized and unlocks the rear doors.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B3809 Rear Door Unlock Relay Circuit
Conditions for Running the DTC
| • | Battery voltage is between 9-16 volts. |
| • | The DTC will set if the rear door unlock function is active or inactive. |
Conditions for Setting the DTC
The DTC will set if the door unlock relay control circuit is shorted to ground or open for more than 1 second.
Action Taken When the DTC Sets
| • | If a short to ground is present on the door unlock relay control circuit, the door unlock relay will be energized and the rear door lock actuators will be held in the unlock position and will not lock. |
| • | If an open condition is present on the door unlock relay control circuit, the rear doors will lock but not unlock. |
Diagnostic Aids
| • | DTC B3809 could also set if the door unlock relay winding is open. |
| • | If both DTC B3808 and B3809 are set as current, the battery positive voltage circuit or the LOCKS fuse could be open. If the LOCKS fuse is open, the cause is most likely one of the following: |
| - | A short to ground in the relay battery positive voltage circuit |
| - | A short to ground in the door lock actuator lock or unlock control circuits |
Conditions for Clearing the DTC
When the fault is no longer present, the BCM changes the current DTC to a history DTC. The BCM will clear the history DTC after 50 fault-free ignition cycles.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Listen for an audible click when the rear door unlock relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
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This step tests for voltage at the coil side of the rear door unlock relay. The LOCKS fuse supplies power to the coil side of the rear door unlock relay.
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This step verifies that the BCM is providing ground to the rear door unlock relay.
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This step tests if ground is constantly being applied to the rear door unlock relay.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Door Lock/Indicator Schematics Connector End View Reference: Power Door Systems Connector End Views or Computer/Integrating Systems Connector End Views in Computer/Integrating Systems | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Does the rear door unlock relay turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 8 | |
Does the test lamp turn ON and OFF with each command? | Go to Step 9 | Go to Step 5 | |
Does the test lamp remain illuminated without being commanded? | Go to Step 7 | Go to Step 6 | |
6 | Test the door unlock relay control circuit of the rear door unlock relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
7 | Test the door unlock relay control circuit of the rear door unlock relay for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
8 | Test for an open or short to ground in the battery positive voltage circuit of the rear door unlock relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 14 | Go to Step 11 |
9 | Inspect for poor connections at the rear door unlock relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 12 |
10 | Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 13 |
11 | Repair the short to ground in the door lock actuator lock or unlock control circuits. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 14 | -- |
12 | Replace the rear door unlock relay. Did you complete the replacement? | Go to Step 14 | -- |
13 | Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 14 | -- |
14 |
Does the DTC reset? | Go to Step 2 | System OK |
