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Home >> Chevy Truck >> 2013 >> Silverado 3500 4WD V8-6.0L (CNG) >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> B Code Charts >> B0780 >> MP 1625/1626-NQF - Transfer Case

MP 1625/1626-NQF - Transfer Case




DTC B0780

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 B0780 01
- 4 Low Indicator Circuit Short to Battery

DTC B0780 06
- 4 Low Indicator Circuit Short to Ground or Open

Diagnostic Fault Information






Circuit/System Description

The 4 low indicator circuit consists of a light emitting diode (LED), a LED feed circuit and a LED control circuit. The indicator dimming control circuit is the LED feed circuit and continuously supplies voltage to the 2 High, 4 High and 4 Low LEDs. When the 4 Low mode has been selected by the driver, the transfer case shift control module (TCCM) provides a ground through the 4 Low indicator control circuit illuminating the LED. The TCCM tests the 4 Low indicator circuit for unexpected voltage by monitoring the B+ supplied by the BCM on the indicator dimming control circuit by grounding the 4 Low indicator control circuit for 2 seconds during the bulb test at key ON.

Conditions for Running the DTC

B0780 01

* Ignition ON.

* System voltage 10-18 V.

* Instrument panel lights not dimmed.

* Daylight running lights MUST be commanded ON.

* Circuit tested when the 4 Low indicator is commanded ON.

B0780 06

* Ignition ON.

* System voltage 10-18 V.

* Instrument panel lights not dimmed.

* Daylight running lights MUST be commanded ON.

* Circuit tested when the 4 Low indicator is commanded OFF.

Conditions for Setting the DTC

B0780 01

The TCCM detects 3.4 V or greater on the 4 Low indicator control circuit when the 4 Low indicator is commanded ON.

B0780 06

The TCCM detects 1.6 V or less for 1.5 seconds on the 4 Low indicator control circuit when the 4 Low indicator is commanded OFF.

Action Taken When the DTC Sets

Normal operation, the SERVICE 4WD indicator is not commanded ON. Driver is informed of fault via bulb check.

Conditions for Clearing the DTC

* The TCCM clears the DTC once the condition for setting the DTC is no longer present.

* A history DTC clears after 40 consecutive warm up cycles without a fault present.

* History DTCs can be cleared using a scan tool.

Diagnostic Aids

* A TRUE B+ has enough current to light a test light.

* A DIAGNOSTIC B+ is a low current circuit that DOES NOT have enough current to light a test light.

* A short to ground on the 4 Low indicator control circuit will cause the 4 Low indicator to remain ON at all times.

* An open or high resistance on the 4 Low indicator to be inoperative during the 2 second bulb check.

* An open in the indicator dimming control circuit will cause the 2 High, 4 High and 4 Low mode indicators to be inoperative during the 2 second bulb check.

* The EL-49741 - Harnessis a good source for 9 V.

* The EL-49742 - Harnessis a good source for B+ and ground.

* With key REMOVED - opening a door puts a true B+ on the indicator dimming control circuit, TCSCS X1 pin 4. Other possible voltages are listed below:

- Door open, key removed - indicator dimming control circuit voltage = true B+.

- Door open, key in, key OFF - indicator dimming control circuit voltage = true B+.

- Door open, key ON, engine OFF - indicator dimming control circuit voltage = diagnostic B+.

- All doors closed, key OFF - indicator dimming control circuit voltage = B+ (high current - enough to light a test light).

- All doors closed, key ON, engine OFF - indicator dimming control circuit voltage = diagnostic B+.

- Key ON, engine OFF. Place a shop light on the DRL sensor. When the DRL sensor commands the headlights OFF, the indicator dimming control circuit voltage, TCSCS X1 pin 4, will go from a diagnostic B+ to a true B+.

Reference Information

Schematic Reference

Transfer Case Control Schematics MP 1625/1626-NQF - Transfer Case

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

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 Control Module References for scan tool information.

Special Tools

* J 35616 - GM-Approved Terminal Test Kit

* EL-49741 - 9 V+ Power Source Harness

* EL-49742 - Battery Voltage B+ and Ground Source Harness

Circuit/System Verification

Key ON, engine OFF. The TCCM runs a 2 second bulb test on all indicators of the TCSCS at key ON.

Circuit/System Testing

Note: When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J 35616 - Kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.

1. Remove key. Disconnect the X1 connector at the transfer case shift control switch (TCSCS).

2. Door open, key ON, engine OFF. Using the L-BU probe J 35616-64B, test for a diagnostic B+ (+0.0/-1.0 V) between the indicator dimming control circuit, TCSCS X1 pin 4 and a good ground, such as the ground terminal of the EL-49742 Harness, black terminal.

• If the voltage is less than the specified range, test the affected circuit for an open/high resistance, short to ground or short to voltage. If all circuits and connections test normal, test the body control module (BCM) for proper operation.

3. Using the L-BU probe J 35616-64B, test for a diagnostic B+ (+0.0/-1.0 V) between the indicator dimming control circuit, TCSCS X1 pin 4 and the 4 Low indicator control circuit, TSCSC X1 pin 10.

• If the voltage is less than the specified range, test the 4 Low indicator control circuit for an open/high resistance or short to power. If all circuits and connections test normal, test the TCCM for proper operation.

4. Key OFF. Using the L-BU probe J 35616-64B, test for greater than 10 ohms between the indicator dimming control circuit, TCSCS X1 pin 4 and all other pins of the TCSCS X1.

• If the resistance is less than the specified range, test the affected circuits for a shorted together condition. If all circuits and connections test normal, test the TCCM for proper operation.

5. Using the L-BU probe J 35616-64B, test for greater than 10 ohms between the 4 Low indicator control circuit, TCSCS X1 pin 10 and all other pins of the TCSCS X1.

• If the resistance is less than the specified range, test the affected circuits for a shorted together condition. If all circuits and connections test normal, test the TCCM for proper operation.

6. Test the TCSCS for proper operation.

Component Testing

BCM

1. Key OFF. Disconnect the X1 connector at the TCSCS.

2. Using the L-BU probe J 35616-64B, connect a test light between the indicator dimming control circuit, TCSCS harness X1 pin 4 and a good ground.

3. Key ON, engine OFF. The test light should be dull or off.

• If the test light is bright, test the indicator dimming control circuit for a short to voltage condition. If all circuits and connections test normal, replace the BCM.

Note: When the DRL sensor turns the headlights OFF, the indicator dimming control circuit voltage, TCSCS X1 pin 4, will go from a diagnostic B+ to a true B+.

4. Place a shop light on the DRL sensor. When the headlights go out the test light should illuminate brightly.

• If the test light is dull or OFF, test the indicator dimming control circuit for an open/high resistance or short to ground condition. If all circuits and connections test normal, replace the BCM.

TCCM

1. Key OFF. Disconnect the X1 connector at the TCSCS.

2. Key ON, engine OFF.

3. Using the L-BU probe J 35616-64B, test for 4.5-5.5 V between the 5-volt reference circuit, TCSCS harness X1 pin 11 and a good ground.

• If the voltage is greater than the specified range, test the 5-volt reference circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.

• If the voltage is less than the specified range, test the 5-volt reference circuit for an open/high resistance or short to ground. If all circuits and connections test normal, replace the TCCM.

4. Using the L-BU probe J 35616-64B, connect a test light between the 5-volt reference circuit, TCSCS harness X1 pin 11 and a good ground. The test light should illuminate dimly.

• If the test light does not illuminate, obtain a different test light and repeat step 4.

5. Key OFF. Wait 30 seconds for the TCCM to shut down.

Note: The TCCM must see the added resistance of the test light on the control circuit at key ON or the TCCM will shut the control circuit drivers OFF. Volt meters will not work for this test.

6. Using the L-BU probe J 35616-64B, connect a test light between the TCSCS harness as specified below for the LED control circuit being tested.

7. Key ON, engine OFF.

8. Using the special function ability of the scan tool, command the affected LED ON and OFF. The test light should turn ON and OFF as commanded.

• If the test light remains illuminated when commanded OFF, test the affected control circuit for a short to ground. If all circuits and connections test normal, replace the TCCM.

• If the test light remains OFF when commanded ON, test the affected control circuit for an open/high resistance or short to voltage. If all circuits and connections test normal, replace the TCCM.





TCSCS

1. Using the L-BU probe J 35616-65B, connect the 9 V power source EL49741 Harness to the TCSCS as specified below for the LED being tested. Connecting the harness to the opposite pins will not illuminate the LED.

2. Connect a 9 V battery to the 9 V power source EL49741 Harness.

3. Verify that only the indicator being tested illuminates.

• If the indicator does not illuminate when tested or the incorrect indicator illuminates, replace the TCSCS.





Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Transfer Case Selector Switch Replacement (With SLT) Transfer Case Selector Switch Replacement (With SLT)Transfer Case Selector Switch Replacement (Without SLT) Transfer Case Selector Switch Replacement (Without SLT)

* Control Module References Control Module References for TCSCM replacement, setup, and programming

* Transfer Case High/Low Clutch Reset Transfer Case High/Low Clutch Reset

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