Stoplamps

Special Tool(s)

	Fluke 77-IV Digital Multimeter FLU77-4 or equivalent
	Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool
	Flex Probe Kit 105-R025D or equivalent

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

The Body Control Module B (BCM-B) monitors the input from the stoplamp switch. When the brake pedal is applied, voltage is routed to the BCM-B . The BCM-B then supplies voltage to the rear stoplamps and high mounted stoplamp.

The ABS module can also send a command to turn the stoplamps on. During an event (such as stability assist) where the ABS module applies the brakes, the ABS module sends a message over the Medium Speed Controller Area Network (MS-CAN) to the BCM-B to turn the stoplamps on.

Field-Effect Transistor (FET) Protection

Field-Effect Transistor (FET) is a type of transistor that when used with module software can be used to monitor and control current flow on module outputs. The FET protection strategy is used to prevent module damage in the event of excessive current flow.

The BCM-B utilizes a FET protective circuit strategy for many of its outputs (for example, a headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A continuous DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short ( FET protection) and the circuit remains shorted, the FET protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. Each FET protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET and the ability of the FET to withstand it. A module lifetime level of fault events is established based upon the durability of the FET . If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, the continuous DTC that was stored on the first failure cannot be cleared by a command to clear the continuous DTCs. The module does not allow this code to be cleared or the circuit restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC U1000:00 and the associated continuous DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When the first or second level is reached, the continuous DTC (associated with the short circuit) sets along with DTC U1000:00. These DTCs can be cleared using the module on-demand self-test, then the Clear DTC operation on the scan tool (if the on-demand test shows the fault corrected). The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then DTC U3000:49 sets along with the associated continuous DTC. This DTC cannot be cleared and the module must be replaced.

The BCM-B FET protected output circuits for the stoplamp system are the high mounted stoplamp and LH/RH rear stoplamp output circuits.

Inspection and Verification

1. Verify the customer concern.

2. Visually inspect for obvious signs of mechanical or electrical damage.
   
   

     Visual Inspection Chart

   Mechanical	Electrical
   Stoplamp switch	Battery Junction Box (BJB) fuse 24 (10A) LED lamp Wiring, terminals or connectors Rear lamp jumper harness High mounted stoplamp Smart Junction Box (SJB)

   
   

3. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.

4. NOTE: Make sure to use the latest scan tool software release.

   If the cause is not visually evident, connect the scan tool to the Data Link Connector (DLC).

5. NOTE: The Vehicle Communication Module (VCM) LED prove-out confirms power and ground from the DLC are provided to the VCM .

   If the scan tool does not communicate with the VCM :
   • Check the VCM connection to the vehicle.
   • Check the scan tool connection to the VCM .
   • Refer to Section 418-00 , No Power To The Scan Tool, to diagnose no power to the scan tool.

6. If the scan tool does not communicate with the vehicle:
   • Verify the ignition key is in the ON position.
   • Verify the scan tool operation with a known good vehicle.
   • Refer to Section 418-00 to diagnose no response from the PCM.

7. Carry out the network test.
   • If the scan tool responds with no communication for one or more modules, refer to Section 418-00 .
   • If the network test passes, retrieve and record the continuous memory DTCs.

8. Clear the continuous DTCs and carry out the self-test diagnostics for the BCM-B .

9. If the DTCs retrieved are related to the concern, go to the Diagnostic Trouble Code (DTC) Chart in this section. For all other DTCs, refer to the Diagnostic Trouble Code (DTC) Chart in Section 419-10 .

10. If no DTCs related to the concern are retrieved, GO to Symptom Chart .

Symptom Chart

Pinpoint Tests

Pinpoint Test I: All The Stoplamps Are Inoperative

Refer to Wiring Diagrams Cell 90 , Turn Signal/Stop/Hazard Lamps for schematic and connector information.

Normal Operation

The stoplamp switch is supplied voltage from the Battery Junction Box (BJB) fuse 24 (10A). When the brake pedal is applied, the stoplamp switch routes voltage to the Body Control Module B (BCM-B) indicating a request to turn the high mounted stoplamp and rear stoplamps on.

This pinpoint test is intended to diagnose the following:

• Fuse
• Wiring, terminals or connectors
• Stoplamp switch
• BCM-B

PINPOINT TEST I: ALL THE STOPLAMPS ARE INOPERATIVE

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

Pinpoint Test J: One Or More Stoplamps Are Inoperative

Refer to Wiring Diagrams Cell 90 , Turn Signal/Stop/Hazard Lamps for schematic and connector information.

Normal Operation

When the Body Control Module B (BCM-B) detects the brake pedal is applied, the BCM-B provides voltage to the high mounted stoplamp and each individual LED lamp within the LH and RH rear stoplamps.

This pinpoint test is intended to diagnose the following:

• Wiring, terminals or connectors
• Rear lamp jumper harness
• LED lamp
• High mounted stoplamp
• BCM-B

PINPOINT TEST J: ONE OR MORE STOPLAMPS ARE INOPERATIVE

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

Pinpoint Test K: The Stoplamps Are On Continuously

Refer to Wiring Diagrams Cell 90 , Turn Signal/Stop/Hazard Lamps for schematic and connector information.

When the brake pedal is applied, the stoplamp switch routes voltage to the Smart Junction Box (SJB), the PCM and Body Control Module B (BCM-B). When the BCM-B detects the brake pedal is applied, the BCM-B provides voltage to the high mounted stoplamp and the LH/RH rear stoplamps.

This pinpoint test is intended to diagnose the following:

• Wiring, terminals or connectors
• Stoplamp switch
• BCM-B
• SJB
• PCM

PINPOINT TEST K: THE STOPLAMPS ARE ON CONTINUOUSLY