Circuit Description
The body control module (BCM) controls the driver door unlock relay. Voltage is applied to the driver door unlock relay through the driver door unlock relay control circuit when the BCM senses a door unlock switch activation or a keyless entry unlock command.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B3127 LF Door Only Unlock Circuit Low |
| • | DTC B3128 LF Door Only Unlock Circuit High |
Conditions for Running the DTC
Battery positive voltage is between 9-16 volts.
Conditions for Setting the DTC
| • | The BCM detects an open in the driver door unlock relay control. This condition must be present for more than 0.3 seconds. |
| • | The BCM detects a short to ground in the driver door unlock relay control while commanding the driver door unlock relay. This condition must be present for more than 0.3 seconds. |
Action Taken When the DTC Sets
| • | The driver door unlock relay will be inoperative. |
| • | The BCM stores either DTC B3127 or DTC B3128 in memory. |
Conditions for Clearing the DTC
| • | A history DTC will clear after 100 consecutive fault free ignition cycles. |
| • | A scan tool may be used to clear the DTC. |
Diagnostic Aids
| • | The following conditions may cause the DTC to set: |
| - | An open or short to ground in the driver door unlock relay control circuit |
| - | A faulty driver door unlock relay |
| - | The BCM is shorted to ground internally. |
| • | If the DTCs are a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Listen for an audible noise when the driver door unlock relay is commanded. Command the door locks to lock and unlock. Repeat the commands as necessary.
-
Verifies that the BCM is providing voltage to the driver door unlock relay.
-
Tests for an open in the driver door unlock relay ground circuit.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Door Lock/Indicator Schematics Connector End View Reference: Power Door Systems Connector End Views | |||
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 driver door lock actuator unlock when commanded? | Go to Diagnostic Aids | Go to Step 3 | |
Does the test lamp flash when the driver door unlock relay is commanded ON? | Go to Step 4 | Go to Step 5 | |
Connect a test lamp between the driver door unlock relay ground circuit and battery positive voltage. Does the test lamp illuminate? | Go to Step 7 | Go to Step 8 | |
5 | Test for an open or short to ground in the driver door unlock relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 6 |
6 | Inspect for poor connections at 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 11 | Go to Step 9 |
7 | Inspect for poor connections at the driver 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 11 | Go to Step 10 |
8 | Repair the open in the driver door unlock relay ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 11 | -- |
9 | 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 11 | -- |
10 | Replace the driver door unlock relay. Did you complete the replacement? | Go to Step 11 | -- |
11 |
Does the DTC reset? | Go to Step 2 | System OK |
