B388A
DTC B388A
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.
DTC Descriptor
DTC B388A 01
- Trailer Park Lamps Circuit Short to Battery
DTC B388A 02
- Trailer Park Lamps Circuit Short to Ground
DTC B388A 04
- Trailer Park Lamps Circuit Open
Diagnostic Fault Information
Circuit/System Description
The trailer park lamp relay is supplied with battery voltage at all times. The trailer park lamp signal circuit is grounded by turning the headlamp switch. The body control module (BCM) energizes the trailer park lamp relay by applying ground to the trailer park lamp relay control circuit. When the trailer park lamp relay is energized, the relay switch contacts close and battery voltage is applied through the trailer park lamp relay fuse to the trailer park lamp supply voltage circuit which illuminates the trailer park lamps if a trailer is connected.
Conditions for Running the DTC
When the trailer park lamp relay is actively being requested by the BCM.
Conditions for Setting the DTC
B388A 01
The BCM detects a short to voltage on the park lamp supply voltage/marker lamp supply voltage circuit.
B388A 02
The BCM detects a short to ground on the park lamp supply voltage/marker lamp supply voltage circuit
B388A 04
The BCM detects an open/high resistance on the park lamp supply voltage/marker lamp supply voltage circuit
Action Taken When the DTC Sets
B388A 01 or B388A 04
The trailer park lamps are inoperative
B388A 02
The trailer park lamps are always ON
Conditions for Clearing the DTC
* The DTC will be current for as long as the fault is present.
* When the fault is no longer present, the DTC will be a history DTC.
* A history DTC will clear after 40 ignition cycles.
Reference Information
Schematic Reference
Trailer Connector/Provision Schematics (Trailer Connector/Provision Schematics)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Circuit/System Verification
Ignition ON, observe the function of the trailer tail lamps while commanding the Trailer Park Lamps ON and OFF with a scan tool. The trailer tail lamps should turn ON and OFF while changing between the commanded states.
Circuit/System Testing
1. Ignition OFF, disconnect the trailer park lamp relay.
2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 86 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
3. Connect a test lamp between the control circuit terminal 85 and the B+ circuit terminal 86.
4. Command the Trailer Park Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM
5. If all circuits test normal, test or replace the trailer park lamp relay.
Component Testing
Relay Test
1. Ignition OFF, disconnect the trailer park lamp relay.
2. Test for 60-180 ohm between terminals 85 and 86.
• If not within the specified range, replace the trailer park lamp relay.
3. Test for infinite resistance between the following terminals:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If not the specified value, replace the trailer park lamp relay.
4. Install a 5 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohm between terminals 30 and 87.
• If greater than the specified range, replace the trailer park lamp relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning)for BCM replacement, programming and setup