Component Testing GMC Sierra 2500 HD

Component Testing

1. Turn the ignition off and check the motor windings for an internal short to ground inside the motor by probing either the motor A control pin and taking the other lead to ground, or the same can be done using motor B control pin. Motor control A is pin A and motor B control is pin D. If the DMM indicates and short to ground replace the transfer case actuator. If nothing is found continue to the next step.
2. With a DMM check the resistance of the motor windings by probing pin A and pin D on the transfer case actuator. The DMM should indicate 0.3-40 ohms, if it does not replace the transfer case actuator and complete the motor learn procedure. If the actuator is within specifications then replace the transfer case control module, program, and complete the motor learn procedure.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC C0379

1. The ignition is ON.
2. System voltage is 10.5-18 volts.

1. This DTC sets if the front axle actuator switch shows battery voltage when the actuator is disengaged, or when the front axle actuator shows no voltage when the actuator is engaged.
2. The module also monitors the axle actuator control circuit and sets the DTC if a high voltage is expected (disengaged) and a low voltage is seen. It will also set when a low voltage is expected (engaged) and a high voltage is seen.

1. The front axle may be engaged at all times or disengaged at all time depending on the failure type.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
2. A history DTC clears after 40 consecutive warm up cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

When the circuits operating the lock solenoid are not complete the lock is engaged. When the circuit is completed the lock is disengaged.

The Ignition 1 voltage circuit and the axle actuator control circuit must be tested for opens, shorts to ground, shorts to voltage, and high resistance. This can also result from a electrically faulted actuator.

1. With the ignition on check which DTC is set. If DTC C0379 is set with failure type byte 08 then do the following: Shift the vehicle into 4 high and look at the scan tool data list to see if the front axle actuator is engaging. If the axle actuator can be heard engaging but the scan tool still indicates disengaged then check the axle switch signal circuit for an open or high resistance. Shift the vehicle to 2 high, if the scan tool indicates the axle actuator is engaged then check the axle switch signal for a short to voltage. If everything checks out go to the next step.
2. Remove the front axle actuator and try to shifting from 4WD to 2WD and see if the states change. If the states change then inspect the front axle for mechanical conditions. Refer to «Four-Wheel Drive Does Not Engage»(ref-278081-S23231764732008012100000) or «Four-Wheel Drive Does Not Disengage»(ref-278081-S37074489712008012100000) . If this checks out then go to the next step.
3. Disconnect the connector at the front axle actuator and check for battery voltage on the ignition 1 circuit. Also check the front axle actuator ground for proper connections. If these circuit test bad repair as necessary checking inline connectors X110 and X109. If these circuits test good go to the next step.
4. Check the axle actuator control circuit for an open, short to ground, or short to voltage. If the actuator control circuit checks good, then short the actuator control circuit to ground at the transfer case control module connector X1 pin 15. This should cause the actuator to engage, remove the ground and then reinstate the ground and the actuator should disengage. If the front axle actuator engages and disengages then replace the transfer case control module, program, and complete the motor learn procedure. If it does not fully engage or disengage then replace the front axle actuator.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC C0387

1. The ignition is ON.
2. System voltage is 10.5-18 volts.

1. A shift request was received but could not be completed within 15 seconds causing this DTC to set.
2. An incomplete shift is one that cannot reach the desired mode or range and cannot return to the original mode or range.
3. If the shift lever detent shaft were to bind, or there was a mechanical failure, or motor A control and motor B control were shorted together the shift would not be completed. This will cause the DTC to set in order to protect the system components from damage.
4. A faulty transfer case shift control module can cause incorrect incremental sensor or motor current measurements which would also result in this DTC setting.
5. Intermittent motor A/B or incremental sensor circuit wiring failures can also cause this DTC to set.

1. All shifting is disabled until condition is corrected.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
3. DTC C0569 4B is set.

1. The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
2. A history DTC clears after 40 consecutive warm up cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

Motor control A shorting to motor control B could cause this DTC.

1. If either DTC C0306 or DTC C0396 is set, diagnose these DTCs first.
2. Using a DMM, with the Ignition off, check to see if motor A control and motor B control are shorted together after disconnecting the transfer case control module and the transfer case actuator. If motor A control is shorted to motor B control repair the circuits as necessary. If the circuits checked good go to next step.
3. Inspect the actuator connector for damage or corrosion. If corrosion is found then repair the damage and attempt an ATC motor learn procedure. If unable to complete motor learn go to next step.
4. Replace the transfer case shift control module with known good unit and attempt an ATC motor learn. If the ATC motor learn is successful then system is OK, if not then proceed to next step.
5. Remove the transfer actuator and check to see if the shift detent shaft is binding. If the shift lever detent shaft is binding refer to «Transfer Case Disassemble»(ref-278047-S35157409902008012100000) . If the shift lever detent shaft is not binding replace the transfer case actuator.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC C0396

1. The ignition is ON.
2. System voltage is 10.5-18 volts.

1. The transfer case control module sees a incremental 8-volt reference signal that is not between 1.5-8.2 volts indicating a short to ground or open if low and a short to voltage if high.
2. The module does not receive a incremental impulse signal voltage between 0.5-4.6 volts.
3. The incremental low reference circuit has an open or high resistance.

1. All shifting is disabled until the condition no longer exists.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
2. A history DTC clears after 40 consecutive warm up cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

An open, high resistance, or short to voltage on the incremental sensor direction signal circuit will cause this DTC to set. If the sensor is determined to be bad the entire transfer case actuator will have to be replaced as the incremental sensor is part of the actuator and can not be replaced independently.

The incremental sensor impulse signal circuit, incremental direction signal circuit, incremental sensor low reference circuit, and the 8-volt reference circuit will need to be check for a short to ground, open, high resistance, and a short to voltage using the following steps

1. Disconnect the connector at the transfer case actuator and check the 8-volt reference signal on pin G at the transfer case actuator with a DMM, ignition on, the voltage should read 7.8-8.2 volts. If the voltage does not read within the specifications then check the 8-volt reference circuit for a short to voltage, open, high resistance, or short to ground. If the circuit checks good and the voltage is out of range replace the transfer case control module, program, and perform the motor learn procedure. If the circuit checks good continue to next step.
2. At the transfer case actuator, with a jumper harness short the 8-volt reference circuit pin G to the incremental impulse signal pin E and note the voltage on the scan tool data display. If the voltage does not read 7.8-8.2 volts check the incremental impulse signal circuit for and open, high resistance, short to ground, or short to voltage. If the circuit checks good then go to the next step.
3. Check the incremental direction circuit for an open, short to ground, high resistance, or a short to voltage by probing pin F at the transfer case actuator and pin 14 and transfer case control module connector X2. If all circuit test good replace the transfer case actuator and perform the motor learn procedure.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC C0550

1. The ignition is ON.
2. System voltage is 10.5-18 volts.

The EEPROM, RAM and ROM, and ECM Microprocessor do self checks against one another and the data does not match causing the DTC to set.

1. Shifting is still disabled until the DTC has cleared itself.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
2. A history DTC clears after 40 consecutive warm up cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

It is sometimes possible to set this DTC falsely due to low voltage. Attempt to clear this DTC and retest.

1. If this DTC sets attempt to clear the DTC and Retest.
2. If the DTC is cleared, but then resets then replace the transfer case control module, program, and complete the transfer case motor learn procedure.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC C0569

1. The ignition is ON.
2. System voltage is 10.5-18 volts.

The motor learn procedure for a new module has not been performed.

1. Shifting is still disabled until the motor learn procedure has been performed.
2. The SERVICE 4WD indicator will be illuminated for this DTC.

The transfer case shift control module clears the DTC if the motor learn procedure has been successfully performed.

Perform the motor learn procedure before normal operation will occur.

Perform the motor learn procedure.

1. Perform the «Diagnostic System Check - Vehicle»(ref-278018-S19353494792008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-278018-S03493196652008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-278018-S38264170562008012100000) provides an overview of each diagnostic category.

DTC C0896

1. The ignition is ON.
2. System voltage is 10.5-18.5 volts.

The voltage is above 18.5 volts or below 10.5 volts for 15 seconds.

1. Shifting is disabled until the voltages change to be within the specifications.
2. The SERVICE 4WD will illuminate for the remainder for the ignition cycle.

1. The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
2. A history DTC clears after 40 consecutive warm up cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

Perform the motor learn procedure before normal operation will occur.

1. If the voltage is low check the voltage on other vehicle systems to determine if this is a vehicle wide condition and take appropriate actions. If this is transfer case specific check the ignition 3 feed to the transfer case control module and the ground for the transfer case control module for proper connections.
2. If the voltage is high, this is likely a vehicle issue such as an alternator problem or the vehicle has been hooked up improperly during a jump start.
3. After the condition is corrected perform the motor learn procedure.