Buick Regal: DTC B388B or B388C
Diagnostic Instructions
- Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
- Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
- Diagnostic Procedure Instructions provides an overview of each
diagnostic category.
DTC Descriptors
DTC B388B 02
Secondary Left Tail and Brake Lamp Circuit Short to Ground
DTC B388B 04
Secondary Left Tail and Brake Lamp Circuit Open
DTC B388C 02
Secondary Right Tail and Brake Lamp Circuit Short to Ground
DTC B388C 04
Secondary Right Tail and Brake Lamp Circuit Open
Diagnostic Fault Information
Circuit/System Description
When the headlamp switch is placed in either the park or low beam position,
ground is applied to the tail
lamp signal circuit to the body control module (BCM). The brake pedal position
sensor provides an
analog voltage signal to the BCM. The BCM sends this messages to the trailer
lighting control module.
The trailer lighting control module responds by applying battery voltage to the
left and right tail lamp
control circuits illuminating the tail lamps.
Conditions for Running the DTC
- Battery voltage must be between 9 - 16 V.
- Brake/tail lamp ON.
Conditions for Setting the DTC
DTC B388B 02
The trailer lighting control module detects a short to ground in the
secondary left tail and brake lamp
control circuit.
DTC B388B 04
The trailer lighting control module detects an open in the secondary left
tail and brake lamp control
circuit.
DTC B388C 02
The trailer lighting control module detects a short to ground in the
secondary right tail and brake lamp
control circuit.
DTC B388C 04
The trailer lighting control module detects an open in the secondary right
tail and brake lamp control
circuit.
Actions Taken When the DTC Sets
The appropriate brake/tail lamp is inoperative.
Conditions for Clearing the DTC
- The condition responsible for setting the DTC no longer exists and the
ignition is cycled.
- A history DTC will clear once 100 consecutive malfunction-free ignition
cycles have occurred.
Reference Information
Schematic Reference
Exterior Lights Wiring Schematics
Connector End View Reference
COMPONENT CONNECTOR END VIEWS - INDEX
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
- Circuit Testing
- Connector Repairs
- Testing for Intermittent Conditions and Poor Connections
- Wiring Repairs
Scan Tool Reference
Control Module References for scan tool information.
Circuit/System Testing
1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the
appropriate component
listed below. It may take up to 2 min for all vehicle systems to power down.
- E51L Tail Lamp Assembly - Auxiliary Left
- E51R Tail Lamp Assembly - Auxiliary Right
2. Test for less than 5 Ω between the ground circuit terminal D and ground.
- Ignition OFF.
- Test for less than 2 Ω in the ground circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, repair the open/high resistance in the ground
connection.
- Go to next step: If less than 5 Ω
3. Connect a test lamp between the control circuit terminal A and ground,
ignition ON
4. Verify the test lamp turns ON and OFF when commanding the appropriate
Auxiliary Tail and
Brake Lamp test ON and OFF with a scan tool.
- If the test lamp is always OFF
- Ignition OFF, disconnect the X1 harness connector at the K68 Trailer
Lighting Control
Module.
- Test for infinite resistance between the control circuit and ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- Go to next step: If infinite resistance
- Test for less than 2 Ω in the control circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K68 Trailer Lighting Control Module.
- If the test lamp is always ON
- Ignition OFF, disconnect the X1 harness connector at the K68 Trailer
Lighting Control
Module, ignition ON.
- Test for less than 1 V between the control circuit terminal and ground.
- If 1 V or greater, repair the short to voltage on the circuit.
- If less than 1 V, replace the K68 Trailer Lighting Control Module.
- Go to next step: If the test lamp turns ON and OFF
5. Test or replace the appropriate E51 Tail Lamp Assembly - Auxiliary.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
- Tail Lamp Replacement (5-Door Hatchback 68) Tail Lamp Replacement
(5-Door Wagon 35)
- Control Module References for trailer lighting control module
replacement, programming, and
setup
READ NEXT:
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
Diag
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
Diag
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
Diag
SEE MORE:
Removal Procedure
1. Upper Intermediate Steering Shaft - Remove.
2. Recover the refrigerant. Refrigerant Recovery and Recharging (R-1234yf).
3. Drain the coolant. Cooling System Draining and Filling (Static) Cooling
System Draining and Filling (GE
47716).
4. Engine Control Module - Remove.
5.
SPECIFICATIONS
FASTENER TIGHTENING TORQUE SPECIFICATIONS
Reusable Threaded Fastener Tightening Specifications
NOTE:
All fasteners listed in this table can be reused after removal.
SCHEMATIC WIRING DIAGRAMS
HVAC WIRING SCHEMATICS
HVAC Module Power, Ground, Serial Data, and Subsystem References
HVAC