Engine Cooling System GMC Sierra 2500

Fastener Tightening Specifications

Fastener Tightening Specifications

Scheme 1

Scheme 2

Scheme 3

Diagnostic Code Index

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

Typical Scan Tool Data

FC Ckt Open, Short Gnd, and Short Volts Test Status

Circuit/System Description

The engine control module (ECM) pulse width modulates (PWM) a 12-volt signal from the cooling fan relay, to control the cooling fan relay ON time. The cooling fan relay varies the voltage drop across the cooling fan clutch solenoid in relation to the pulse width modulated signal from the ECM, which allows the cooling fan to operate at variable speeds.

Conditions for Running the DTC

1. The ignition voltage is greater than 11 volts.
2. The engine is operating.
3. The engine speed is greater than 600 RPM.
4. DTC P0480 runs continuously when the conditions above exist for greater than 3 seconds.

Conditions for Setting the DTC

The ECM detects that the commanded state of the ECM driver, and the actual state of the cooling fan relay control circuit do not match for greater than 1 second.

Action Taken When the DTC Sets

DTC P0480 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0480 is a Type B DTC.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Engine operating, command the cooling fan clutch ON to 80 % and then OFF to 0 % with a scan tool. Observe the scan tool Test Status parameters listed below: FC Ckt Open Test Status FC Ckt Short Gnd Test Status FC Ckt Short Volts Test Status The parameters should display OK or Not Run in each of the commanded states.
2. Observe the DTC information with a scan tool. Verify DTC P0480 is not set.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the cooling fan clutch relay.
2. Test for less than 5 ohms between the fan relay ground circuit terminal 6 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal 2 and ground. If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition voltage circuit fuse is open, test the fan relay controlled output circuit and the fan clutch solenoid for a short to ground, repair or replace as necessary. If the relay controlled output and clutch solenoid test normal, test or replace the fan clutch relay.
4. Test for 3-4 V between the relay control circuit terminal 5 and ground. If less than the specified range, test the relay control circuit for an open, or for a short to ground. If the circuit tests normal, replace the ECM. If greater than the specified range, test the relay control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
5. Connect a 3 A fused jumper wire between the relay control circuit terminal 5 and ground. Observe the scan tool FC Ckt Short Gnd Test Status parameter. The parameter should transition from OK to Fault when the control circuit is connected to ground. If the parameter does not respond as specified, test the relay control circuit for a high resistance. If the circuit tests normal, replace the ECM.
6. If all circuits test normal, test or replace the cooling fan clutch relay.

Component Testing

Relay Test

1. Remove the cooling fan clutch relay.
2. Connect a 10 A fused jumper wire between relay terminal 2 and B+. Connect a jumper wire between relay terminal 6 and ground.
3. Test for less than 1 V between terminal 4 and ground. If greater than the specified value, replace the fan relay.
4. Connect a jumper wire between terminal 5 and ground.
5. Test for B+ between terminal 4 and ground. If less than the specified value, replace the fan relay.

EV Fan Clutch Solenoid Valve Test-Static

1. Disconnect the harness connector at the cooling fan clutch.
2. Measure the resistance between the terminals listed below. The DMM should display OL. B and C B and D B and E B and the fan clutch housing/ground If less than the specified range, test the circuits of the jumper harness for an open/shorted condition. If the jumper harness tests normal, replace the cooling fan clutch assembly.
3. Test for 7-17 ohms between terminal B and terminal A of the jumper harness connector. If not within the specified range, test the circuits of the jumper harness for an open/shorted condition. If the jumper harness tests normal, replace the fan clutch assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

FC Relay 1, and FC Relay 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status

The engine cooling fan system consists of 2 electric cooling fans and 3 fan relays. The cooling fan relays are arranged in a series/parallel (S/P) configuration. This allows the engine control module (ECM) to operate both fans together at low or high speeds using 2 fan control circuits. The cooling fans receive positive voltage from the cooling fan relays, which receive battery positive voltage from the underhood fuse block. The cooling fans are supplied a ground at G100 and G101.

1. The system voltage is between 9-32 volts.
2. The engine speed is greater than 400 RPM.
3. DTCs P0480 and P0481 run continuously when the conditions above are met.

1. The commanded state of the ECM driver and the actual state of the control circuit do not match.
2. The condition exists for greater than 5 seconds.

DTCs P0480 and P0481 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0480 and P0481 are Type B DTCs.

Diagnostic Aids

1. The ECM has the capability of providing command to the fan relays even when a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.
2. The scan tool cooling fan output control operates as follows: Fan Relay 1 operates both fans at a low speed Fan Relay 2 and 3 operates one fan at high speed Fan Relays 1, 2, and 3 operates both fans at high speed

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX»(/gmc/sierra-2500/2012-2012/remont/body-electrical/#wiring-systems-and-power-management-component-connector-end-views-index)
2. «Electrical Center Identification Views»(/gmc/sierra-2500/2012-2012/remont/electrical-component-locations/#wiring-systems-and-power-management-component-locator-electrical-center-identification-views)

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References

1. Engine operating, observe the DTC information with a scan tool. DTC P0480 or P0481 should not be set.
2. Command the cooling fans ON and OFF at high speed while observing the scan tool circuit test status parameters listed below: FC Relay 1 Ckt Open, Short Gnd, and Short Volts Test Status FC Relay 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status The parameters should display OK or Not Run in each of the commanded states.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the 3 cooling fan relays listed below: FAN LO relay FAN CNTRL relay FAN HI relay
2. Ignition ON, verify that a test lamp illuminates between ground and the ignition circuit terminal 85 of each relay. If the test lamp does not illuminate, test the ignition circuit for an open/high resistance.
3. Set the DMM on the diode setting. Connect the black lead to ground. Connect the red lead of the DMM to a control circuit terminal listed below: FAN LO Relay terminal 86 FAN CNTRL Relay terminal 86 FAN HI Relay terminal 86 The DMM should display OL. If less than the specified range, test the appropriate relay coil control circuit for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module.
4. Command the appropriate cooling fan relay ON and OFF with a scan tool. The DMM should transition from OL when commanded OFF to less than 1 V when commanded ON. If the circuit voltage does not correspond to the specified values, test the control circuit for an open/high resistance or for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module.
5. If all circuits test normal, test or replace the appropriate KR20 Cooling Fan Relay.

1. Ignition OFF, disconnect the KR20 Cooling Fan Relay.
2. Test for 70-110 ohms between terminals 85 and 86. If not within the specified range, replace the KR20 Cooling Fan Relay.
3. Measure the resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 The DMM should display OL. If less than the specified range, replace the KR20 Cooling Fan Relay.
4. Test the KR20 Fan Control Relay for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the fan control relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the KR20 Cooling Fan Relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
3. «Engine Coolant Fan Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
4. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

FC Relay 1, 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status

FC Relay 1, 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status

The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan control circuits, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on cooling requirements. The ECM controls the five relays by grounding the relay control circuits.

To operate the fans, the ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage. When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage.

1. The ignition voltage is between 11-32 volts.
2. The engine speed is greater than 0 RPM.
3. DTC P0480, P0481, and P0482 run continuously when the conditions above are met.

1. The commanded state of the ECM driver and the actual state of the control circuit do not match.
2. The condition exists for greater than 5 seconds.

DTCs P0480, P0481 and P0482 are Type B DTCs.

DTCs P0480, P0481 and P0482 are Type B DTCs.

1. The ECM has the capability of providing command to the fan relays even when a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.
2. The scan tool cooling fan output control operates as follows: Fan Relay 1 operates both fans at a low speed. Fan Relay 2 operates both fans at medium speed. Fan Relays 1, 2, and 3 operates both fans at high speed.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX»(/gmc/sierra-2500/2012-2012/remont/body-electrical/#wiring-systems-and-power-management-component-connector-end-views-index)
2. «Electrical Center Identification Views»(/gmc/sierra-2500/2012-2012/remont/electrical-component-locations/#wiring-systems-and-power-management-component-locator-electrical-center-identification-views)

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References

1. Engine operating, observe the DTC information with a scan tool. DTC P0480, P0481, or P0482 should not be set.
2. Command the cooling fans ON and OFF at high speed while observing the scan tool circuit test status parameters listed below: FC Relay 1 Ckt Open, Short Gnd, and Short Volts Test Status FC Relay 2 Ckt Open, Short Gnd, and Short Volts Test Status FC Relay 3 Ckt Open, Short Gnd, and Short Volts Test Status The parameters should display OK or Not Run in each of the commanded states.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, open the hood to disable the Auto-Stop function.
2. Ignition ON, verify the scan tool hood position parameter displays Open. If the hood position does not display Open, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) for DTC P254F.
3. Ignition OFF, disconnect all 5 cooling fan relays.
4. Ignition ON, verify that a test lamp illuminates between ground and the ignition circuit terminal of each relay listed below: FAN LO Relay terminal 85 FAN MID 1 Relay terminal 85 FAN CNTRL Relay terminal 86 FAN MID 2 Relay terminal 86 FAN HI Relay terminal 86 If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all the components connected to the ignition voltage circuit and replace as necessary.
5. Set the DMM on the diode setting. Connect the black lead to ground. Connect the red lead of the DMM to a control circuit terminal listed below: FAN LO Relay terminal 86 FAN MID 1 Relay terminal 86 FAN CNTRL Relay terminal 85 FAN MID 2 Relay terminal 85 FAN HI Relay terminal 85 The DMM should display OL. If less than the specified range, test the appropriate relay coil control circuit for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module.
6. Command the appropriate cooling fan relay ON and OFF with a scan tool. The DMM should transition from OL when commanded OFF to less than 1 V when commanded ON. If the circuit voltage does not correspond to the specified values, test the control circuit for an open/high resistance or for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module.
7. If all circuits test normal, test or replace the appropriate KR20 Cooling Fan Relay.

1. Ignition OFF, disconnect the KR20 Cooling Fan Relay.
2. Test for 50-90 ohms between terminals 85 and 86. If not within the specified range, replace the KR20 Cooling Fan Relay.
3. Measure the resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 The DMM should display OL. If less than the specified range, replace the KR20 Cooling Fan Relay.
4. Test the KR20E Cooling Fan Speed Control Relay for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the KR20E Cooling Fan Speed Control Relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the KR20 Cooling Fan Relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
3. «Engine Coolant Fan Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
4. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The cooling fan relay sends a pulse width modulated (PWM) signal of 12-14 volts to the cooling fan clutch through the cooling fan clutch solenoid voltage control circuit. The cooling fan relay varies the voltage drop across the cooling fan clutch solenoid in relation to a pulse width modulated signal from the ECM in order to control the speed of the cooling fan. The signal controls the position of the oil control valve inside the cooling fan clutch housing.

1. DTC P0016, P007C, P007D, P0112, P0113, P0117, P0118, P0335, P0336, P0340, P0341, P0480, P0495, or P0526 is not set.
2. The engine is operating for greater than 10 seconds.
3. The engine speed is between 1, 200-3, 780 RPM.
4. The BARO is greater than 75 kPa.
5. The engine coolant temperature is warmer than 70°C (158°F).
6. The charge air cooler (CAC) down stream temperature is warmer than -7°C (19°F).
7. The ECM commanded fan duty cycle is greater than 36 percent.
8. The cooling fan input shaft speed is steady.
9. DTC P0483 runs continuously every 100 mS when the conditions above exist.

1. The difference between the desired and the actual cooling fan speeds is 500 RPM or greater.
2. The condition exists for 2 minutes.

DTC P0483 is a Type B DTC.

DTC P0483 is a Type B DTC.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, inspect the cooling fan and the drive belt for the following conditions: A loose, worn, or mis-routed drive belt Oil leaks at the cooling fan clutch A free-spinning cooling fan A seized cooling fan clutch A broken cooling fan
2. Ignition ON, observe the DTC information with a scan tool. Verify DTC P0480 or P0526 is not set, if either DTC is set diagnose that DTC first.
3. Operate the engine at 1, 500 RPM while slowly commanding the cooling fan clutch from 10 % to 80 %, then return to 10 %. Observe the difference between the scan tool Fan Speed and Desired Fan Speed parameters throughout the test. The difference between the parameters should be less than 500 RPM throughout the speed transition.
4. Observe the DTC information with a scan tool. Verify DTC P0483 is not set.
5. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the cooling fan clutch relay.
2. Test for less than 5 ohms between the fan relay ground circuit terminal 6 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Disconnect the harness connector at the cooling fan clutch.
4. Test for less than 5 ohms between the fan clutch solenoid valve ground circuit terminal A and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
5. Install the fan clutch relay.
6. Connect a test lamp between the cooling fan clutch solenoid voltage control circuit terminal B and ground.
7. Engine operating, command the fan clutch relay to 50 % with a scan tool. The test lamp should illuminate and flash ON and OFF. If the test lamp does not illuminate, test the solenoid voltage control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the fan clutch relay. If the test lamp illuminates without flashing, test the solenoid voltage control circuit for a short to voltage. If the circuit tests normal, replace the fan clutch relay.
8. If all the circuit/connections test normal, test or replace the cooling fan clutch assembly.

Relay Test

1. Remove the cooling fan clutch relay.
2. Connect a 10 A fused jumper wire between relay terminal 2 and B+. Connect a jumper wire between relay terminal 6 and ground.
3. Test for less than 1 V between terminal 4 and ground. If greater than the specified value, replace the fan relay.
4. Connect a jumper wire between terminal 5 and ground.
5. Test for B+ between terminal 4 and ground. If less than the specified value, replace the fan relay.

EV Fan Clutch Solenoid Valve Test-Static

1. Disconnect the harness connector at the cooling fan clutch.
2. Measure the resistance between the terminals listed below. The DMM should display OL. B and C B and D B and E B and the fan clutch housing/ground If less than the specified range, test the circuits of the jumper harness for an open/shorted condition. If the jumper harness tests normal, replace the cooling fan clutch assembly.
3. Test for 7-17 ohms between terminal B and terminal A of the jumper harness connector. If not within the specified range, test the circuits of the jumper harness for an open/shorted condition. If the jumper harness tests normal, replace the fan clutch assembly.

EV Fan Clutch Solenoid Valve Test-Dynamic

1. Ignition OFF, disconnect the harness connector at the cooling fan clutch.
2. Connect a jumper wire between terminal A of the jumper harness connector and ground.
3. Connect a 10 A fused jumper wire to terminal B of the jumper harness connector.
4. Connect the 10 A fused jumper wire to B+. The fan should get much louder to indicate the clutch is engaged.
5. Disconnect the 10 A fused jumper wire from B+. The fan should become quiet to indicate the clutch is disengaged. If the fan clutch doesn't engage or disengage according to the test, replace the cooling fan clutch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The cooling fan relay sends a pulse width modulated (PWM) signal of 12-14 volts to the cooling fan clutch through the cooling fan clutch solenoid voltage control circuit. The cooling fan relay varies the voltage drop across the cooling fan clutch solenoid in relation to a pulse width modulated signal from the ECM in order to control the speed of the cooling fan. The signal controls the position of the oil control valve inside the cooling fan clutch housing.

1. DTC P0016, P0112, P0113, P0117, P0118, P0335, P0336, P0340, P0341, P0480, P0483, P0526, P2228, or P2229 is not set.
2. The engine is operating for greater than 10 seconds.
3. The engine speed is greater than 1, 181 RPM.
4. The engine OFF time after the previous ignition cycle was greater than 0 seconds.
5. The ambient air temperature (AAT) is warmer than -40°C (-40°F).
6. The BARO is greater than 55 kPa.
7. The ECM commanded fan duty cycle is less than 45 percent.
8. DTC P0495 runs continuously when the conditions above exist.

1. The cooling fan speed is greater than 1, 500 RPM for 80 seconds. OR
2. The clutch fluid pump-out, which is the time it takes for the fan clutch to disengage completely, is greater than a range of 10 minutes at sea level to 52 minutes at elevations of 6, 500 ft.

DTC P0495 is a Type B DTC.

DTC P0495 is a Type B DTC.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, verify the fan clutch is not seized or binding.
2. Ignition ON, observe the DTC information with a scan tool. Verify DTC P0480, P0483, or P0526 is not set, if a DTC is set diagnose that DTC first.
3. Engine idling at operating temperature with all accessories turned OFF, for greater than 10 minutes.
4. Observe the scan tool DTC information. Verify DTC P0495 is not set. If the DTC is set, replace the cooling fan clutch assembly.
5. Operate the engine at 1, 500 RPM for 2 minutes. Observe the DTC information with a scan tool. Verify DTC P0495 is not set. If the DTC is set, replace the cooling fan clutch assembly.
6. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the harness connector at the cooling fan clutch.
2. Connect a test lamp between the cooling fan clutch solenoid voltage control circuit terminal B and ground.
3. Engine operating, command the fan clutch relay to 50 % with a scan tool. The test lamp should illuminate and flash ON and OFF. If the test lamp illuminates without flashing, test the solenoid voltage control circuit for a short to voltage. If the circuit tests normal, replace the fan clutch relay.
4. If all the circuit/connections test normal, test or replace the cooling fan clutch assembly.

Relay Test

1. Remove the cooling fan clutch relay.
2. Connect a 10 A fused jumper wire between relay terminal 2 and B+. Connect a jumper wire between relay terminal 6 and ground.
3. Test for less than 1 V between terminal 4 and ground. If greater than the specified value, replace the fan relay.
4. Connect a jumper wire between terminal 5 and ground.
5. Test for B+ between terminal 4 and ground. If less than the specified value, replace the fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The engine control module (ECM) uses the cooling fan speed signal in order to determine the actual fan speed in relation to the desired fan speed. The ECM uses the cooling fan speed signal in order to reduce the cooling fan noise and maintain the powertrain cooling requirements. The ECM supplies a 5-volt reference and low reference circuit to clutch hall effect sensor in the cooling fan clutch. The hall effect sensor returns a signal pulse through the signal circuit in response to the reluctor track, which is located inside the fan clutch.

1. The engine is operating for greater than 10 S.
2. The engine speed is grater than 550 RPM.
3. The ECM commanded fan duty cycle is greater than 45 percent.
4. DTC P0526 runs continuously when the conditions above exist for greater than 30 S.

1. The ECM detects a loss of cooling fan speed signal for greater than 300 mS.
2. The ECM detects that the cooling fan speed signal is greater or less than a predetermined threshold.
3. DTC P0526 sets if either condition above exists for greater than 3 S.

DTC P0526 is a Type B DTC.

DTC P0526 is a Type B DTC.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Observe the DTC information with a scan tool. Verify DTC P06D2 is not set. If the DTC is set, refer to «DTC P0641, P0651, P0697, P06A3, P06D2, or P06D6»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-66l-lgh-lml-dtc-p0545-to-dtc-p2080) .
2. Observe the DTC information with a scan tool. Verify DTC P0526 is not set.
3. Engine operating, observe the scan tool Fan Speed parameter. The parameter should display a fan speed greater than 0 RPM.
4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the harness connector at the cooling fan clutch.
2. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 5 ohms between low reference circuit terminal C and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal E and ground. If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
4. Test for 4.8-5.2 V between the signal circuit terminal D and ground. If less than the specified range, test for a short to ground or an open/high resistance. If circuit test normal, replace the ECM. If greater than specified range, test for a short to voltage. If circuit test normal, replace the ECM. If the circuit test normal, test the circuits of the fan clutch jumper harness for an open/shorted condition.
5. If all the circuit/connections test normal, test or replace the cooling fan clutch assembly.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over-termperature condition. This condition occurs when the coolant temperature is above a calibrated value for a calibrated length of time. The ECM will disable half of the cylinders by turning OFF the fuel injectors. By disabling half of cylinders, the ECM is able to reduce the temperature of the coolant.

The engine is operating.

All V8

The coolant temperature is warmer than 129°C (264°F) for greater than 10 seconds.

6.0L-Hybrid

The coolant temperature is warmer than 132°C (270°F) for greater than 10 seconds.

1. DTC P1258 is a Type A DTC.
2. The engine will operate in the Overheated Engine Protection Operating Mode.
3. The engine coolant temperature indicator lamp, if equipped, will illuminate.
4. The driver information center (DIC), if equipped, may display a message.
5. If the protection mode is active and an ECT sensor DTC sets, the protection mode will activate during the next drive cycle until the ECT sensor DTC runs and passes.

DTC P1258 is a Type A DTC.

Description and Operation

1. «Cooling System Description and Operation»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Instrument Cluster Description and Operation»(/gmc/sierra-2500/2012-2012/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
3. «Indicator/Warning Message Description and Operation»(/gmc/sierra-2500/2012-2012/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
4. «Audible Warnings Description and Operation»(/gmc/sierra-2500/2012-2012/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges__audible-warnings-description-and-operation)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Note. If DTC P0480, P0481, or P0482 is set, diagnose that DTC first.

1. Observe the engine coolant level. The engine coolant level should be within operating range. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill)
2. Ensure that the vehicle has the correct engine coolant, with correct concentration, and is not old, contaminated or contains additives. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill)
3. Inspect the cooling system for the following: Leaks Kinked or pinched hoses, especially at the radiator Loose, missing, or damaged radiator air seals or deflectors The radiator and A/C condenser for any air flow obstructions or bent fins-Refer to «Symptoms - Engine Cooling»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Command the cooling fans ON in each available speed with a scan tool. If the cooling fans are inoperative in any of the commanded states, refer to «Cooling Fan Inoperative (without HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Cooling Fan Inoperative (with HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Cooling Fan Inoperative (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Test the thermostat for correct operation. Refer to «Thermostat Diagnosis»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__thermostat-diagnosis) .
2. Test the engine cooling system for overheating. Refer to «Engine Overheating»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__engine-overheating) .
3. Inspect the water pump and coolant flow for correct operation. Refer to «Water Pump Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__water-pump-replacement-v6) , «Water Pump Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Water Pump Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Inspect the engine for worn/leaking/cracked cylinder heads and engine block. Refer to «Coolant in Combustion Chamber»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-diagnostic-information-and-procedures__coolant-in-combustion-chamber) , and «Coolant in Engine Oil»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-diagnostic-information-and-procedures__coolant-in-engine-oil) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Important Preliminary Inspections Before Starting

Before using the Symptom diagnosis, perform the following

1. Perform «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) and verify all of the following items: Ensure that the engine control module (ECM) and indicator lamp are operating correctly. Ensure that there are no diagnostic trouble codes (DTCs) that are stored. Scan tool data is within a normal operating range. Refer to «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for scan tool information.
2. Verify the customer concern.
3. Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help reveal the cause of an intermittent condition.
4. Locate the correct symptom. Perform the tests and inspections associated with the symptom.

Review the cooling fan and cooling system operation in order to familiarize yourself with the system functions.

1. «Cooling Fan Description and Operation (Gas)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Cooling Fan Description and Operation (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Cooling System Description and Operation»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)

Visual/Physical Inspection

Several of the symptom procedures call for a careful visual and physical inspection. This can lead to correcting a condition without further tests and can save time. This inspection should include the following areas

1. Ensure that the control module grounds are clean, tight, and correctly located.
2. Inspect cooling system hoses and pipes for splits, kinks, and proper connections. Inspect thoroughly for any type of a leak or a restriction.
3. Inspect for a dirty or restricted radiator and HVAC condenser.
4. Inspect for aftermarket devices which could affect the operation of the Cooling System.
5. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
6. Inspect the surge tank reservoir for the proper coolant level.

Identifying Intermittent Conditions

Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movement of a component. Refer to the following for a list to help determine an intermittent condition

1. Moisture and water intrusion in connectors, terminals, and components
2. Connector mating
3. Terminal contact
4. High circuit or component resistance-High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component.
5. Harness that is located too tight, or chaffed circuits
6. High or low ambient temperature
7. High or low engine coolant temperatures
8. High underhood temperatures
9. Heat build up in component or circuit due to circuit resistance, poor terminal contact, or high electrical load
10. High or low system voltage
11. High vehicle load conditions
12. Rough road surface
13. Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge
14. Incorrect installation of non-factory, aftermarket, and after factory add on accessories

If an intermittent is determined, refer to Testing for Intermittent Conditions and Poor Connections for specific strategies in diagnosing intermittent conditions.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Cooling Fan Always On (with HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Cooling Fan Always On (without HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Cooling Fan Inoperative (without HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Cooling Fan Inoperative (with HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Cooling Fan Inoperative (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
3. «Engine Overheating»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__engine-overheating)
4. «Loss of Coolant»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__loss-of-coolant)
5. «Thermostat Diagnosis»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__thermostat-diagnosis)
6. «Coolant Heater Inoperative (without Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Inoperative (with Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
7. «Engine Fails To Reach Normal Operating Temperature»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__engine-fails-to-reach-normal-operating)
8. «Fan Clutch Diagnosis»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-diagnosis) , «Fan Clutch Diagnosis (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The engine cooling system contains an engine coolant level switch to alert the driver in the event of a low coolant level. The coolant level switch is mounted at the lowest point in the cooling system surge tank. If the amount engine of coolant in the surge tank drops below the level of the switch, the coolant level switch opens. The coolant level switch signal circuit is monitored by the heating, ventilation, and air conditioning (HVAC) control module. If the HVAC control module detects an open circuit, or a high voltage condition on the signal circuit for greater than 10 seconds, a Class 2 message is sent to the instrument panel cluster (IPC), requesting display of the low coolant level message.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling System Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

1. Ignition OFF, verify the radiator surge tank is filled to the correct level, with engine coolant.
2. Ignition ON or with the engine operating, observe the driver information center (DIC). The low engine coolant level message should not be displayed.

Note. Circuit/System Verification must be performed before performing the Circuit/System Testing.

1. Ignition OFF, disconnect the harness connector at the B33 coolant level switch.
2. Test for less than 5 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a 3 A fused jumper wire between the B33 signal circuit terminal A and the ground circuit terminal B.
4. Engine operating, observe the DIC. Verify the low engine coolant level message does not display. If the message continues to be displayed, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the K33 HVAC control module.
5. If all circuits test normal, replace the B33 coolant level switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Radiator Surge Tank Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC module replacement, setup, and programming

Repair Verification

Verify that the low coolant indicator is OFF with the engine coolant at the proper level.

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The engine cooling fan system consists of 2 electric cooling fans and 3 fan relays. The cooling fan relays are arranged in a series/parallel (S/P) configuration. This allows the engine control module (ECM) to operate both fans together at low or high speeds using 2 fan control circuits. The cooling fans receive positive voltage from the cooling fan relays, which receive battery positive voltage from the underhood fuse block. The cooling fans are supplied a ground at G100 and G101.

The ECM has the capability of providing command to the fan relays even while a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

1. Verify that the following DTCs are not set: P0480 or P0481. If a DTC is set, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) .
2. Ignition ON, verify with a scan tool that the control module is not commanding fan activation.
3. Ignition ON, observe that the fans are not activated.

1. Ignition OFF, disconnect each cooling fan relay one at a time.
2. Ignition ON, observe that the fans are not activated. If the fans are activated, test for a short to voltage in the relay controlled output circuit. If the fans are not activated, test or replace the appropriate cooling fan relay.

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 70-110 ohms between terminals 85 and 86. If not within the specified range, replace the cooling fan relay.
3. Measure the resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 The DMM should display OL. If less than the specified range, replace the cooling fan relay.
4. Test the Fan Control Relay for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the cooling fan relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the cooling fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.

The ECM has the capability of providing command to the fan relays even while a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Verify that the following DTCs are not set: P0480, P0481, P0482. If a DTC is set, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) .
2. Verify with a scan tool that the ECM is not commanding fan relay activation.
3. Ignition ON, observe that the fans are not activated.

1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to «Hybrid Modes of Operation Description»(/gmc/sierra-2500/2012-2012/remont/body-electrical/#hybridev-control-system__hybrid-modes-of-operation-description) .
2. Ignition ON, verify the scan tool hood position parameter displays Open. If the hood position does not display Open, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) for DTC P254F.
3. Ignition OFF, disconnect each cooling fan relay one at a time.
4. Ignition ON, observe that the fans are not activated. If the fans are activated, test for a short to voltage in the relay controlled output circuit. If the fans are not activated, test or replace the appropriate cooling fan relay.

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 50-90 ohms between terminals 85 and 86. If not within the specified range, replace the cooling fan relay.
3. Measure the resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 The DMM should display OL. If less than the specified range, replace the cooling fan relay.
4. Test the Fan Control Relay for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the cooling fan relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the cooling fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Fan Low Relay

Fan Control Relay

Fan High Relay

The engine cooling fan system consists of 2 electric cooling fans and 3 fan relays. The cooling fan relays are arranged in a series/parallel (S/P) configuration. This allows the engine control module (ECM) to operate both fans together at low or high speeds using 2 fan control circuits. The cooling fans receive positive voltage from the cooling fan relays, which receive battery positive voltage from the underhood fuse block. The cooling fans are supplied a ground at G100 and G101.

1. The ECM has the capability of providing command to the fan relays even while a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.
2. The scan tool cooling fan output control operates as follows: Fan Relay 1 operates both fans at a low speed Fan Relay 2 and 3 operates one fan at high speed Fan Relay 1, 2, and 3 operates both fans at high speed

Schematic Reference

Engine Cooling Schematics

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480 or P0481 is not set. If a DTC is set, refer to «DTC P0480 or P0481 (without HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Ignition ON, command high and low speed fans ON and OFF with a scan tool. Verify that both fans turn ON and OFF when changing between the commanded states.

Note. You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the cooling fan relays.
2. Connect a 30 A fused jumper between the Fan Control relay switch circuit terminal 30 and the relay ground circuit terminal 87. This will complete the left side fan ground circuit. Leave this jumper in place for the remainder of this procedure.
3. Ignition ON, verify that a test lamp illuminates between ground and the relay switched ignition circuit terminal listed below: Fan Low Relay terminal 30 Fan High Relay terminal 30 If the test lamp does not illuminate, test the appropriate relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the appropriate G10 cooling fan.
4. Connect a 30 A fused jumper between the cooling fan relay circuit terminals listed below: Fan High Relay terminals 87 and 30 Fan Low Relay terminals 87 and 30 Verify the appropriate fan is activated. If the corresponding cooling fan does not activate, test the relay controlled output circuit and the cooling fan ground circuit for an open/high resistance. If the circuits tests normal, test or replace the appropriate G10 cooling fan. If the corresponding cooling fan activates, replace the appropriate cooling fan relay.
5. Install the Fan Control Relay. Verify both fans activate at low speed. If both fans do not activate, test the Fan Control Relay switched output circuit terminal 87A for a short to ground or an open/high resistance.
6. If all the circuits test normal, test or replace the Fan Control Relay.

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 70-110 ohms between terminals 85 and 86. If not within the specified range, replace the cooling fan relay.
3. Measure the resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 The DMM should display OL. If less than the specified range, replace the cooling fan relay.
4. Test the Fan Control Relay for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the cooling fan relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the cooling fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Engine Coolant Fan Motor Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
3. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.

1. The ECM has the capability of providing command to the fan relays even when a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.
2. The scan tool cooling fan output control operates as follows: Fan Relay 1 operates both fans at a low speed Fan Relay 2 operates both fans at medium speed Fan Relays 1, 2, and 3 operates both fans at high speed

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480 or P0481 is not set. If a DTC is set, refer to «DTC P0480, P0481, or P0482 (with HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Ignition ON, command the cooling fans ON and OFF at high, medium, and low speed with a scan tool. Verify that both fans turn ON and OFF when changing between the commanded states.

Note. You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to «Hybrid Modes of Operation Description»(/gmc/sierra-2500/2012-2012/remont/body-electrical/#hybridev-control-system__hybrid-modes-of-operation-description) .
2. Ignition ON, verify the scan tool hood position parameter displays Open. If the hood position does not display Open, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) for DTC P254F.
3. Ignition OFF, disconnect the cooling fan relays.
4. Ignition ON, verify that a test lamp illuminates between the Fan Control relay ground circuit terminal 87 and B+. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
5. Connect a 30 A fused jumper between the Fan Control relay switch circuit terminal 30 and the relay ground circuit terminal 87. This will complete the left side fan ground circuit. Leave this jumper in place for the remainder of this procedure.
6. Ignition ON, verify that a test lamp illuminates between ground and the relay switched ignition circuit terminal listed below: Fan Low Relay terminal 87 Fan Mid 1 Relay terminal 87 Fan Mid 2 Relay terminal 30 Fan High Relay terminal 30 If the test lamp does not illuminate, test the appropriate relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the appropriate G10 cooling fan.
7. Connect a 30 A fused jumper between the cooling fan relay circuit terminals listed below: Fan High Relay terminals 87 and 30 Fan Low Relay terminals 87 and 30 Verify the appropriate fan is activated. If the corresponding cooling fan does not activate, test the relay controlled output circuit and the cooling fan ground circuit for an open/high resistance. If the circuits tests normal, test or replace the appropriate G10 cooling fan.
8. Connect a 30 A fused jumper between the cooling fan relay circuit terminals listed below: Fan Mid 1 Relay terminal 87 and 30 Fan Mid 2 Relay terminal 30 and 87 The appropriate fan should activate and operate at a reduced speed. If the corresponding cooling fan does not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the appropriate R10 cooling fan resistor. If the corresponding cooling fan activates, replace the appropriate cooling fan relay.
9. Ignition OFF, install the Fan Control relay.
10. Ignition ON, connect a 30 A fused jumper wire between the Fan Low relay terminals 87 and 30. Both cooling fans should activate and operate at a low speed. If both fans do not activate, test the Fan Control Relay switched output circuit terminal 87A for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the Fan Control relay.
11. If all the circuits test normal, test or replace the appropriate cooling fan relay.

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 50-90 ohms between terminals 85 and 86. If not within the specified range, replace the cooling fan relay.
3. Measure the resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 The DMM should display OL. If less than the specified range, replace the cooling fan relay.
4. Test the Fan Control Relay for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the cooling fan relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the cooling fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
3. «Engine Coolant Fan Motor Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
4. «Engine Coolant Fan Resistor Replacement (Right HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Resistor Replacement (Left HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The ECM controls the EV fan clutch operation. The ECM regulates a 12-volt pulse width modulated signal (PWM) to the cooling fan relay. The PWM signal determines the ON time of the relay. As the ECM command increases, so does the ON time of the relay. The relay ON time directly controls the amount of time the solenoid, which is internal to the fan clutch, is energized. When the solenoid in the fan clutch is energized, it opens the spring loaded valve and allows fluid to flow from the storage chamber to the fluid coupling of the cooling fan clutch, which increases the fan speed. When the solenoid is de-energized, the spring loaded valve closes, and allows the fluid in the coupling of the fan clutch to drain back to the storage chamber, which reduces fan speed. The rapid modulation of the fan clutch solenoid valve gives the ECM the ability to precisely control the amount of fluid that remains in the fluid coupler, allowing more effective regulation of the fan speed and powertrain cooling requirements.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX»(/gmc/sierra-2500/2012-2012/remont/body-electrical/#wiring-systems-and-power-management-component-connector-end-views-index)
2. «Electrical Center Identification Views»(/gmc/sierra-2500/2012-2012/remont/electrical-component-locations/#wiring-systems-and-power-management-component-locator-electrical-center-identification-views)

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, inspect the cooling fan and the drive belt for the following conditions: A loose, worn, or mis-routed drive belt Oil leaks at the cooling fan clutch A free-spinning cooling fan A seized cooling fan clutch A broken cooling fan Inspect the cooling fan clutch harness connector X142 and the fan clutch jumper harness for the following conditions: Poorly mated connectors Backed/pushed out connector terminals Poor terminal tension Cut, chaffed, or nicked harness wiring at the fan clutch If a condition is found Repair as necessary If a condition is not found
2. Ignition ON, observe the DTC information with a scan tool. Verify DTC P0480, P0483, P0495, or P0526 is not set. If a DTC is set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) If a DTC is not set
3. Engine at operating temperature, operate the engine at 1, 500 RPM while slowly commanding the cooling fan clutch from 10 % to 80 %, then return to 10 %. Observe the difference between the scan tool Fan Speed and Desired Fan Speed parameters throughout the test. The difference between the parameters should be less than 500 RPM throughout the speed transition. The fan clutch does not operate as specified Refer to Circuit/System Testing below. The fan clutch operates as specified
4. All OK

1. Ignition OFF, disconnect the fan clutch harness connector X142.
2. Test for less than 5 ohms between the fan clutch solenoid valve ground circuit terminal A and ground. If 5 ohms or greater Test the ground circuit for an open/high resistance. If less than 5 ohms
3. Connect a test lamp between the cooling fan clutch solenoid voltage control circuit terminal B and ground.
4. Engine operating, command the fan clutch relay to 50 % with a scan tool. The test lamp should illuminate and flash ON and OFF. If the test lamp does not illuminate Ignition OFF, disconnect the cooling fan clutch relay. Test for less than 5 ohms between the fan relay ground circuit terminal 6 and ground. If 5 ohms or greater Test the ground circuit for an open/high resistance. If less than 5 ohms Test for less than 1 ohms between the relay B+ circuit terminal 2 and the Fan Fuse. If 1 ohms or greater Test the B+ circuit for an open/high resistance. If less than 1 ohms Test for infinite resistance between the fan clutch relay terminal 4 and ground. If less than infinite Test the fan clutch solenoid valve voltage control circuit for a short to ground. If infinite Test for less than 1 ohms between relay terminal 4 and harness connector X142. If 1 ohms or greater Test the fan clutch solenoid valve voltage control circuit for an open/high resistance. If less than 1 ohms Test or replace the fan clutch relay. If the test lamp illuminates and flashes
5. Test for infinite resistance between the terminals of the fan clutch harness connector listed below. B and C B and D B and E B and the fan clutch housing If less than the specified range Test the circuits of the jumper harness for an open/shorted condition. If the jumper harness tests normal, replace the cooling fan clutch assembly. If at the specified range
6. Test for 7-17 ohms between terminal B and terminal A of the fan clutch jumper harness connector. If not within the specified range Test the circuits of the jumper harness for an open/shorted condition. If the jumper harness tests normal, replace the cooling fan clutch assembly. If within the specified range Refer to EV Fan Clutch Solenoid Valve Test-Dynamic below.

Relay Test

1. Remove the cooling fan clutch relay.
2. Connect a 10 A fused jumper wire between relay terminal 2 and B+. Connect a jumper wire between relay terminal 6 and ground.
3. Test for less than 1 V between terminal 4 and ground. If greater than the specified value, replace the fan relay.
4. Connect a jumper wire between terminal 5 and ground.
5. Test for B+ between terminal 4 and ground. If less than the specified value, replace the fan relay.

EV Fan Clutch Solenoid Valve Test-Dynamic

1. Ignition OFF, disconnect the fan clutch jumper harness connector X142.
2. Connect a jumper wire between terminal A of the jumper harness connector and ground.
3. Connect a 10 A fused jumper wire to terminal B of the jumper harness connector.
4. Connect the 10 A fused jumper wire to B+. The fan should get much louder to indicate the clutch is engaged.
5. Disconnect the 10 A fused jumper wire from B+. The fan should become quiet to indicate the clutch is disengaged. If the fan clutch doesn't engage or disengage according to the test, replace the cooling fan clutch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fan Clutch Replacement (Diesel)

Engine Overheating

Engine Overheating

Loss of Coolant

Loss of Coolant

Thermostat Diagnosis

Tools Required

J 24731 Tempil Stick

Use one of the following procedures in testing for a malfunctioning thermostat.

Thermostat Test Procedure Using Tempil Sticks

The coolant thermostat can be tested using a temperature (tempil) stick. The temperature stick is a pencil like device. It has a wax material containing certain chemicals which melt at a given temperature. Temperature sticks can be used to determine a thermostat's operating range, by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing.

1. Use a tempil stick in order to find the opening and the closing temperatures of the coolant thermostat. J 24731 Tempil Stick -188 tempil stick melts at 87°C (188°F). The thermostat should begin to open. J 24731 Tempil Stick -206 tempil stick melts at 97°C (206°F). The thermostat should be fully open.
2. Replace the coolant thermostat if it does not operate properly between this temperature range.

Thermostat Test Procedure Using Glycol

Inspect the operation of the thermostat by hanging the thermostat on a hook in a 50/50 percent solution of DEX-COOL® and clean drinkable water.

In order to inspect if the thermostat valve is opening properly, perform the following test

1. Completely submerge the thermostat in the glycol solution. The solution should be 11°C (22°F) above the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.

In order to inspect if the thermostat valve is closing properly, perform the following test

1. Completely submerge the thermostat in a glycol solution. The solution should be 6°C (10°F) below the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The optional coolant heater is a 1, 000 watt heating element that mounts in the engine block in place of an existing anti-freeze plug. The coolant heater operates using an external 110 volt AC power source and is designed to warm the coolant in the engine block, for improved starting in very cold weather. The coolant heater also helps reduce fuel consumption when a cold engine is warming up. The detachable AC power cord allows the coolant heater to operate at all temperatures whenever it is connected to an AC power source. The power cord is also equipped with a weather shield to protect the plug when not in use.

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

1. Test the engine coolant heater for an open or short to ground. If open or shorted, replace the heater.
2. If the heater tests normal, replace the coolant heater power cord.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Coolant Heater Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Coolant Heater Cord Replacement (LH6, LMG, LY2 and LY5)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Cord Replacement (LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Cord Replacement (LY6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Cord Replacement (L76/L92)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The optional coolant heater is a heating element that mounts in the engine block in place of an existing anti-freeze plug. The coolant heater operates using an external 110 volt AC power source and is designed to warm the coolant in the engine block for improved starting in very cold weather. The coolant heater also helps reduce fuel consumption when a cold engine is warming up. The detachable AC power cord contains an internal thermal switch that opens, to prevent operation when the ambient temperature is warmer than -10°C (14°F), and closes at -18°C (0°F) to allow operation. The power cord is also equipped with a weather shield to protect the plug when not in use.

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Note. The power supply cord will test open due to an internal thermal switch if the ambient temperature is warmer than -10°C (14°F). The thermal switch is designed to close when the ambient temperature is below -18°C (0°F).

1. Test the engine coolant heater for an open or short to ground. If open or shorted, replace the heater.
2. If the heater tests normal, replace the coolant heater power cord.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Coolant Heater Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)
2. «Coolant Heater Cord Replacement (LH6, LMG, LY2 and LY5)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Cord Replacement (LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Cord Replacement (LY6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Cord Replacement (L76/L92)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system)

Engine Fails To Reach Normal Operating Temperature

Engine Fails To Reach Normal Operating Temperature

Pressure Cap Testing

Special Tools

1. J 24460-01 Cooling System Pressure Tester
2. J 42401 Radiator Cap/Surge Tank Test Adapter

1. Remove the pressure cap.
2. Wash the pressure cap sealing surface with water.
3. Use the J 24460-01 cooling system pressure tester (1) with J 42401 radiator cap/surge tank test adapter (2) in order to test the pressure cap.
4. Test the pressure cap for the following conditions: Pressure release when the J 24460-01 cooling system pressure tester exceeds the pressure rating of the pressure cap. Maintain the rated pressure for at least 10 seconds. Note the rate of pressure loss.
5. Replace the pressure cap under the following conditions: The pressure cap does not release pressure which exceeds the rated pressure of the cap. The pressure cap does not hold the rated pressure.

Cooling System Leak Testing

Special Tools

1. J 24460-01 Cooling System Pressure Tester
2. J 42401 Radiator Cap/Surge Tank Test Adapter

1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__pressure-cap-testing) .
3. Wash the pressure cap mating surface with water.
4. Use the J 24460-01 cooling system pressure tester with the J 42401 radiator cap/surge tank test adapter in order to apply pressure to the cooling system. Do not exceed the pressure cap rating.
5. The cooling system should hold the rated pressure for at least 2 minutes. Observe the gauge for any pressure loss.
6. Repair any leaks as required.

Fan Clutch Diagnosis

Fan Clutch Diagnosis

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The ECM controls the EV fan clutch operation. The ECM regulates a 12-volt pulse width modulated signal (PWM) to the cooling fan relay. The PWM signal determines the ON time of the relay. As the ECM command increases, so does the ON time of the relay. The relay ON time directly controls the amount of time the solenoid, which is internal to the fan clutch, is energized. When the solenoid in the fan clutch is energized, it opens the spring loaded valve and allows fluid to flow from the storage chamber to the fluid coupling of the cooling fan clutch, which increases the fan speed. When the solenoid is de-energized, the spring loaded valve closes, and allows the fluid in the coupling of the fan clutch to drain back to the storage chamber, which reduces fan speed. The rapid modulation of the fan clutch solenoid valve gives the ECM the ability to precisely control the amount of fluid that remains in the fluid coupler, allowing more effective regulation of the fan speed and powertrain cooling requirements.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX»(/gmc/sierra-2500/2012-2012/remont/body-electrical/#wiring-systems-and-power-management-component-connector-end-views-index)
2. «Electrical Center Identification Views»(/gmc/sierra-2500/2012-2012/remont/electrical-component-locations/#wiring-systems-and-power-management-component-locator-electrical-center-identification-views)

Description and Operation

Cooling Fan Description and Operation (Gas) , Cooling Fan Description and Operation (Diesel)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF.
2. Verify the conditions listed below do not exist with the cooling fan system: A loose, worn, or mis-routed drive belt Oil leaks at the cooling fan clutch A free-spinning cooling fan A seized cooling fan clutch A broken cooling fan Inspect the cooling fan clutch harness connector and the fan clutch jumper harness for the conditions listed below: Poorly mated connectors Backed/pushed out connector terminals Poor terminal tension Cut, chaffed, or nicked harness wiring at the fan clutch If a condition is found Repair as necessary If a condition is not found
3. Ignition ON.
4. Verify DTC P0480, P0483, P0495, or P0526 is not set. If a DTC is set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) If a DTC is not set
5. Engine at operating temperature.
6. Verify the scan tool Fan Speed and Desired Fan Speed parameters are within 500 RPM while performing the test listed below: Increase engine speed to 1, 500 RPM NOTE: In each of the commanded states, it may take up to 2 minutes for the Fan Speed to achieve the Desired Fan Speed. Command the Cooling Fan slowly from 10 % to 80 % with a scan tool. Command the Cooling Fan to 10 % with a scan tool. The Fan Speed is not within 500 RPM of the Desired Fan Speed Refer to Circuit/System Testing below. The Fan Speed is within 500 RPM of the Desired Fan Speed
7. All OK

1. Ignition OFF, and all vehicle systems OFF, disconnect the cooling fan relay. It may take up to 2 minutes for all vehicle systems to power down.
2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground. If the test lamp does not illuminate Remove the Fan Fuse. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp illuminates
3. Test for less than 5 ohms between the fan relay ground circuit terminal 6 and ground. If 5 ohms or greater Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
4. Test for 7-17 ohms between fan relay terminal 4 and terminal 6. If less than 7 ohms Disconnect the engine cooling fan harness connector. Verify a test lamp does not illuminate between the fan relay terminal 4 and B+. If the test lamp illuminates, repair the short to ground in the solenoid valve control circuit terminal 4. If the test lamp does not illuminate, test the circuits of the jumper harness for a shorted condition. If the jumper harness tests normal, replace the cooling fan clutch assembly. If greater than 17 ohms Disconnect the engine cooling fan harness connector. Test for less than 2 ohms between relay terminal 4 and fan harness connector terminal B. If 2 ohms or greater, repair the open/high resistance in the fan clutch solenoid valve control circuit. If less than 2 ohms. Test for less than 2 ohms between the fan harness connector terminal A and ground. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, test the circuits of the jumper harness for an open/high resistance condition. If the jumper harness tests normal, replace the cooling fan clutch assembly. If within 7-17 ohms
5. Engine operating, connect a 10 A fused jumper wire between fan relay terminal 4 and B+.
6. Verify the fan gets much louder to indicate the fan clutch is engaged.
7. Disconnect the 10 A fused jumper wire from B+. The fan should become quiet to indicate the clutch is disengaged. If the fan clutch doesn't engage or disengage according to the test Replace the cooling fan clutch assembly. If the fan clutch engages and disengages according to the test
8. Test or replace the fan relay.

Relay Test

1. Remove the cooling fan clutch relay.
2. Connect a 10 A fused jumper wire between relay terminal 2 and B+. Connect a jumper wire between relay terminal 6 and ground.
3. Test for less than 1 V between terminal 4 and ground. If greater than the specified value, replace the fan relay.
4. Connect a jumper wire between terminal 5 and ground.
5. Test for B+ between terminal 4 and ground. If less than the specified value, replace the fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fan Clutch Replacement (Diesel)

Cooling System Draining and Filling (Vac-N-Fill Gasoline)

Special Tools

1. GE-47716 Vac-N-Fill Coolant Refill Tool
2. J 26568 Coolant and Battery Tester
3. J 42401 Radiator Cap and Surge Tank Test Adapter

Draining Procedure

1. Park the vehicle on a level surface.
2. Remove the coolant pressure cap.
3. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
4. Place a drain pan under the drain cock and/or lower radiator hose.
5. Reposition the radiator drain cock and/or lower radiator hose.
6. Drain the cooling system.
7. If a complete engine block drain is required, remove the engine block drain plug.
8. Inspect the coolant.
9. Follow the appropriate procedure based on the condition of the coolant. Normal in appearance-Follow the filling procedure. Discolored-Follow the flush procedure. Refer to «Flushing»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__flushing) .

Vac-N-Fill Procedure

Note. To prevent boiling of the coolant/water mixture in the vehicles cooling system, do not apply vacuum to a cooling system above 49°C (120°F). The tool will not operate properly when the coolant is boiling.

1. Install the J 42401 radiator cap and surge tank test adapter.
2. Attach the Van-N-Fill cap to the vehicles coolant fill port.
3. Attach the vacuum gauge assembly to the Vac-N-Fill cap.
4. Attach the fill hose to the barb fitting on the vacuum gauge assembly. Ensure that the valve is closed.
5. Pour the coolant mixture into the graduated reservoir.
6. Place the fill hose in the graduated reservoir.
7. Install the vacuum tank on the graduated reservoir with the fill hose routed through the cut-out area in the vacuum tank.
8. Attach the venture assembly to the vacuum tank.
9. Attach a shop air hose to the venture assembly. Ensure the valve on the venture assembly is closed.
10. Attach the vacuum hose to the vacuum gauge assembly and the vacuum tank.
11. Clamp off the overflow hose.
12. Open the valve on the venture assembly. The vacuum gauge will begin to rise and a hissing noise will be present.
13. Continue to draw vacuum until the needle stops rising. This should be 610-660 mm Hg (24-26 in Hg). Cooling hoses may start to collapse. This is normal due to vacuum draw.
14. To aid in the fill process, position the graduated reservoir above the coolant fill port.
15. Slowly open the valve on the vacuum gauge assembly. When the coolant reaches the top of the fill hose, close the valve. This will eliminate air from the fill hose.
16. Close the valve on the venture assembly.
17. If there is a suspected leak in the cooling system, allow the system to stabilize under vacuum and monitor for vacuum loss. If vacuum loss is observed, refer to «Loss of Coolant»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__loss-of-coolant) .
18. Open the valve on the vacuum gauge assembly. The vacuum gauge will drop as coolant is drawn into the system.
19. Once the vacuum gauge reaches zero, close the valve on the vacuum gauge assembly and repeat steps 11-17.
20. Remove the J 42401 radiator cap and surge tank test adapter.
21. Detach the Vac-N-Fill cap from the vehicles coolant fill port.
22. Add coolant to the system as necessary.
23. Inspect the concentration of the coolant mixture using J 26568 coolant and battery tester.
24. Detach the vacuum hose form the vacuum gauge assembly.
25. Attach the extraction hose to the vacuum hose.
26. Open the valve on the venture assembly to start a vacuum draw.
27. Use the extraction hose to draw out coolant to the proper level.
28. The vacuum tank has a drain valve on the bottom of the tank. Open the valve to drain coolant from the vacuum tank into a suitable container for disposal.

Cooling System Draining and Filling (Vac-N-Fill Diesel)

Special Tools

1. GE-47716 Vac-N-Fill Coolant Refill Tool
2. J-26568 Coolant and Battery Tester
3. J-42401 Radiator Cap and Surge Tank Test Adapter

For equivalent regional tools, refer to Special Tools .

1. Park the vehicle on a level surface.
2. Remove the coolant pressure cap.
3. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
4. Place a drain pan under the drain cock and/or lower radiator hose.
5. Reposition the radiator drain cock and/or lower radiator hose.
6. Drain the cooling system.
7. If a complete engine block drain is required, remove the engine block drain plug.
8. Inspect the coolant.
9. Follow the appropriate procedure based on the condition of the coolant. Normal in appearance-Follow the filling procedure. Discolored-Follow the flush procedure. Refer to «Flushing»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__flushing) .

Note. To prevent boiling of the coolant/water mixture in the vehicles cooling system, do not apply vacuum to a cooling system above 49°C (120°F). The tool will not operate properly when the coolant is boiling.

1. Install the J-42401 adapter.
2. Attach the Van-N-Fill cap to the vehicles coolant fill port.
3. Attach the vacuum gauge assembly to the Vac-N-Fill cap.
4. Attach the fill hose to the barb fitting on the vacuum gauge assembly. Ensure that the valve is closed.
5. Pour the coolant mixture into the graduated reservoir.
6. Place the fill hose in the graduated reservoir.
7. Install the vacuum tank on the graduated reservoir with the fill hose routed through the cut-out area in the vacuum tank.
8. Attach the venture assembly to the vacuum tank.
9. Attach a shop air hose to the venture assembly. Ensure the valve on the venture assembly is closed.
10. Attach the vacuum hose to the vacuum gauge assembly and the vacuum tank.
11. Clamp off the overflow hose.
12. Open the valve on the venture assembly. The vacuum gauge will begin to rise and a hissing noise will be present.
13. Continue to draw vacuum until the needle stops rising. This should be 610-660 mm Hg (24-26 in Hg). Cooling hoses may start to collapse. This is normal due to vacuum draw.
14. To aid in the fill process, position the graduated reservoir above the coolant fill port.
15. Slowly open the valve on the vacuum gauge assembly. When the coolant reaches the top of the fill hose, close the valve. This will eliminate air from the fill hose.
16. Close the valve on the venture assembly.
17. If there is a suspected leak in the cooling system, allow the system to stabilize under vacuum and monitor for vacuum loss. If vacuum loss is observed, refer to «Loss of Coolant»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__loss-of-coolant) .
18. Open the valve on the vacuum gauge assembly. The vacuum gauge will drop as coolant is drawn into the system.
19. Once the vacuum gauge reaches zero, close the valve on the vacuum gauge assembly and repeat steps 11-17.
20. Remove the J-42401 adapter.
21. Detach the Vac-N-Fill cap from the vehicles coolant fill port.
22. Add coolant to the system as necessary.
23. With radiator cap off, start the engine.
24. Run the engine at 2, 000-2, 500 RPM until the engine reaches normal operating temperature. Engine should reach an operating temperature of 90°C (194°F) and the upper radiator hose should be HOT.
25. With the engine in idle, add more coolant until it reaches the top of the bottle.
26. Slowly continue to add coolant so it goes into the overflow side of the bottle until it reaches 1/3 of the capacity.
27. Install the radiator cap.
28. Run the engine at 2500 RPM for 3 minutes.
29. Shut off the engine and remove the key.
30. Inspect the concentration of the engine coolant using the J-26568 tester.
31. Rinse away any excess coolant from the engine and the engine compartment.
32. The vacuum tank has a drain valve on the bottom of the tank. Open the valve to drain coolant from the vacuum tank into a suitable container for disposal.

Cooling System Draining and Filling (Static Fill)

Special Tools

1. J 26568 Coolant and Battery Tester
2. J 38185 Hose Clamp Pliers

1. Follow the steps below in order to remove the surge tank fill cap: Slowly rotate the cap counterclockwise. Stop rotating and allow the hissing to stop. After all the hissing stops, continue turning counterclockwise in order to remove the cap.
2. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
3. Place a drain pan under the lower radiator hose and/or drain cock.
4. Using the J 38185 hose clamp pliers, reposition the lower radiator hose clamp.
5. Reposition the lower radiator hose and/or drain cock from the radiator.
6. Drain the cooling system.
7. If a complete engine block drain is required, remove the left and right engine block coolant drain plugs.
8. Remove the engine block coolant heater, if equipped. Refer to «Coolant Heater Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
9. Inspect the coolant.
10. Follow the appropriate procedure based on the condition of the coolant: Normal in appearance-Follow the filling procedure. Discolored-Follow the flush procedure. Refer to «Flushing»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__flushing) .

Filling Procedure

1. Install the lower radiator hose and/or drain cock to the radiator.
2. Using the J 38185 hose clamp pliers, reposition the lower radiator hose clamp.
3. If the left and right engine block coolant drain plugs were removed, perform the following: Apply pipe sealer to the drain plugs. Install the drain plugs. Tighten Tighten the drain plugs to 60 (44 lb ft).
4. Install the engine block coolant heater, if equipped. Refer to «Coolant Heater Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Lower the vehicle.
6. Slowly fill the cooling system with a 50/50 coolant mixture. Refer to «Approximate Fluid Capacities»(/gmc/sierra-2500/2012-2012/remont/lubrication-system/#maintenance-and-lubrication__approximate-fluid-capacities) .
7. Install the coolant pressure cap.
8. Start the engine.
9. Run the engine at 2, 000-2, 500 RPM until the engine reaches normal operating temperature. Engine should reach an operating temperature of 90°C (194°F) and the upper radiator hose should be HOT.
10. Allow the engine to idle for 3 minutes.
11. Shut the engine OFF.
12. Allow the engine to cool.
13. Top off the coolant as necessary.
14. Inspect the concentration of the engine coolant using the J 26568 coolant and battery tester.
15. Rinse away any excess coolant from the engine and the engine compartment.

Cooling System Draining and Filling (Static Fill LGH, LML)

Special Tools

J-26568 Coolant and Battery Tester

For equivalent regional tools, refer to Special Tools .

1. Follow the steps below in order to remove the surge tank fill cap: Slowly rotate the cap counterclockwise. Stop rotating and allow the hissing to stop. After all the hissing stops, continue turning counterclockwise in order to remove the cap.
2. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
3. Remove the right wheelhouse liner. Refer to «Front Wheelhouse Liner Replacement - Right Side (GMC)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) , «Front Wheelhouse Liner Replacement - Right Side (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
4. Place a drain pan under the lower radiator hose and/or drain cock.
5. Remove quick connect snap ring.
6. Reposition the lower radiator hose and/or drain cock from the radiator.
7. Drain the cooling system.
8. If a complete engine block drain is required, remove the left and right engine block coolant drain plugs.
9. Remove the engine block coolant heater, if equipped. Refer to «Coolant Heater Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
10. Inspect the coolant.
11. Follow the appropriate procedure based on the condition of the coolant: Normal in appearance-Follow the filling procedure. Discolored-Follow the flush procedure. Refer to «Flushing»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__flushing) .

1. Install the lower radiator hose and/or drain cock to the radiator.
2. Reposition the lower radiator hose and install quick connect snap ring.
3. If the left and right engine block coolant drain plugs were removed, perform the following: Apply pipe sealer to the drain plugs. Install the drain plugs and tighten to 60 (44 lb ft).
4. Install the engine block coolant heater, if equipped. Refer to «Coolant Heater Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Coolant Heater Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Install the right wheelhouse liner. Refer to «Front Wheelhouse Liner Replacement - Right Side (GMC)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) , «Front Wheelhouse Liner Replacement - Right Side (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
6. Lower the vehicle.
7. Slowly fill the cooling system with a 50/50 coolant mixture. Refer to «Approximate Fluid Capacities»(/gmc/sierra-2500/2012-2012/remont/lubrication-system/#maintenance-and-lubrication__approximate-fluid-capacities) .
8. Slowly continue filling as the level goes down.
9. With radiator cap off, start the engine.
10. Run the engine at 2, 000-2, 500 RPM until the engine reaches normal operating temperature. Engine should reach an operating temperature of 90°C (194°F) and the upper radiator hose should be HOT.
11. Continue to run the engine at 2, 000-2, 500 for 5 more minutes.
12. Allow the engine to idle for 5 minutes, as you slowly add more coolant to the system.
13. Run the engine at 2, 000-2, 500 RPM for another 5 minutes.
14. With the engine in idle, add more coolant until it reaches the top of the bottle.
15. Slowly continue to add coolant so it goes into the overflow side of the bottle until it reaches 1/3 of the capacity.
16. Install radiator cap.
17. Run the engine at 2500 RPM for 3 minutes.
18. Shut off engine and remove key.
19. Inspect the concentration of the engine coolant using the J-26568 tester.
20. Rinse away any excess coolant from the engine and the engine compartment.

Flushing

Radiator Cleaning

1. Some conditions may require the use of warm water and a mild detergent.
2. Clean the A/C condenser fins.
3. Clean between the A/C condenser and radiator.
4. Clean the radiator cooling fins.
5. Straighten any damaged cooling fins.

Scheme 4

Radiator Surge Tank Replacement (Non-HP2)

Removal Procedure

1. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
2. Reposition the surge tank inlet hose clamp from the radiator.
3. Remove the surge tank inlet hose from the radiator.
4. Reposition the surge tank inlet hose clamp at the surge tank.
5. Remove the surge tank inlet hose (1) from the surge tank.

Installation Procedure

1. Install the surge tank inlet hose (1) to the surge tank.
2. Position the surge tank inlet hose clamp to the surge tank.
3. Install the surge tank inlet hose to the radiator.
4. Position the surge tank inlet hose clamp to the radiator.
5. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .

Scheme 5

Radiator Surge Tank Inlet Hose Replacement (LGH, LML)

Scheme 6

Radiator Inlet Hose Replacement (Non-HP2)

Scheme 7

Radiator Inlet Hose Replacement (LGH, LML)

Scheme 8

Radiator Outlet Hose Replacement (Non-HP2)

Radiator Outlet Hose Replacement (LGH, LML)

Special Tools

J-38185 Hose Clamp Pliers

For equivalent regional tools, Refer to Special Tools

1. Remove the right wheelhouse liner. Refer to «Front Wheelhouse Liner Replacement - Right Side (GMC)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) , «Front Wheelhouse Liner Replacement - Right Side (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
2. Remove the engine shield. Refer to «Engine Splash Shield Replacement - Right Side»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
3. Drain the coolant. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill)
4. Remove the air cleaner outlet duct. Refer to «Air Cleaner Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-66l-lgh-lml-repair-instructions)
5. Reposition the radiator outlet hose clamp (1) at the surge tank using J-38185 pliers
6. Remove the radiator outlet hose (2) from the surge tank.
7. Disconnect the quick connect (1) at the radiator.
8. Reposition the radiator outlet hose clamp (2) at the heater outlet hose using J-38185 pliers
9. Remove the radiator outlet hose clip retainers (3) from the brackets.
10. Remove the radiator outlet hose (4) from the radiator.
11. Remove the radiator outlet hose clamp (1) from the engine.
12. Remove the radiator outlet hose clip retainers (2) from the engine shield.
13. Remove the radiator outlet hose (3) from the vehicle.

1. Install the radiator outlet hose (3) to the vehicle.
2. Install the radiator outlet hose clamp (1) to the engine.
3. Install the radiator outlet hose clip retainers (2) to the engine shield.
4. Install the radiator outlet hose (4) from the radiator.
5. Install the radiator outlet hose clip retainers (3) to the brackets.
6. Reposition the radiator outlet hose clamp (2) at the heater outlet hose using J-38185 pliers
7. Disconnect the quick connect (1) at the radiator.
8. Install the radiator outlet hose (2) to the surge tank.
9. Reposition the radiator outlet hose clamp (1) at the surge tank using J-38185 pliers
10. Install the engine shield. Refer to «Engine Splash Shield Replacement - Right Side»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
11. Install the right wheelhouse liner. Refer to «Front Wheelhouse Liner Replacement - Right Side (GMC)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) , «Front Wheelhouse Liner Replacement - Right Side (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
12. Install the air cleaner outlet duct. Refer to «Air Cleaner Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-66l-lgh-lml-repair-instructions)
13. Fill the coolant. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill)

Scheme 9

Engine Coolant Outlet Pipe Replacement (LGH/LML)

1. Using a bent-tip screwdriver or equivalent, pull on one of the open ends of the retaining ring in order to rotate the retaining ring.
2. Rotate the retaining ring (3) around the quick connector until the retaining ring is out of position and can be completely removed.
3. Remove the radiator outlet hose (2) from the quick connector fitting at the radiator (1).

1. Hook one of the open ends of the retaining ring (3) in one of the slots in the quick connector.
2. Rotate the retaining ring (3) around the connector until the retaining ring is positioned with all 3 ears through the 3 slots.
3. Ensure the 3 retaining ring ears can be seen from the inside of the connector and the retaining ring can move freely in the slots.
4. Install the radiator outlet hose (2) onto the radiator quick connector fitting until a click is heard or felt. Pull back on the radiator outlet hose (2) to ensure a proper connection.

Scheme 10

Radiator Vent Inlet Hose Replacement (Non-HP2)

Scheme 11

Engine Oil Cooler Connector Replacement

1. Disengage the plastic caps from the quick connect fittings. Pull the caps back along the pipe.
2. Using a bent-tip screwdriver or equivalent, pull on one of the open ends of the retaining ring in order to rotate the retaining ring.
3. Rotate the retaining ring around the quick connector until the retaining ring is out of position and can be completely removed. Discard the retaining rings.
4. Remove the engine oil cooler line from the quick connector fitting at the radiator. Refer to «Engine Oil Cooler Hose/Pipe Quick-Connect Fitting Disconnection and Connection»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__engine-oil-cooler-hosepipe-quick-connect-fitting) . Pull the lines straight out from the connectors.
5. Clean all of the components in a suitable solvent, and dry them with compressed air.
6. Inspect the fittings, the connectors, the cooler lines, and the cooler for damage, distortion, or restriction. Replace parts as necessary.

1. Install a new retaining ring into each quick connector fitting.
2. Hook one of the open ends of the retaining ring in one of the slots in the quick connector.
3. Rotate the retaining ring around the connector until the retaining ring is positioned with all 3 ears through the 3 slots.
4. Ensure the 3 retaining ring ears can be seen from the inside of the connector and the retaining ring can move freely in the slots.
5. Install the engine oil cooler line into the quick connector fitting until a click is heard or felt. Pull back on the engine oil cooler lines to ensure a proper connection.
6. Snap the plastic cap onto the quick connect fitting.
7. Ensure that the plastic cap is fully seated against the fitting.
8. Ensure that no gap is present between the cap and the fitting.
9. Inspect and fill the engine oil to the proper level.

Engine Oil Cooler Hose/Pipe Quick-Connect Fitting Disconnection and Connection

Special Tools

1. DT-47731 1/2 in Line Quick Release Tool
2. J 28585 Universal Snap Ring Remover for the 5/8 in Line

1. Remove the plastic caps from the quick connect fittings by pulling the caps back along the pipe before installation.
2. Install the DT-47731 quick release tool onto the engine oil cooler (EOC) pipe, or use the J 28585 universal snap ring remover.
3. Slide the DT-47731 quick release tool toward the EOC pipe fitting, or use the J 28585 universal snap ring remover.
4. Connect the DT-47731 quick release tool onto the EOC pipe fitting.
5. Rotate the DT-47731 quick release tool or use the J 28585 universal snap ring remover until the retainer clip (1) rises above the fitting retainer seat.
6. Pull back on the EOC pipe to disengage the pipe from the EOC pipe fitting.
7. Remove the DT-47731 quick release tool or the J 28585 universal snap ring remover from the EOC pipe.

1. Install the EOC pipe into the EOC pipe fitting. A distinct snap should be heard or felt when assembling the EOC pipe to the fitting.
2. To ensure the cooler line is properly installed, give the cooler pipe a gentle pull.

The optional oil cooler is either an integral part of the radiator or a separate unit placed in front of the radiator. The cooler lines and hoses are serviceable.

1. Disconnect the engine oil cooler quick connect fittings. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. If equipped with regular production option (RPO) L76 (6.0L) engine, perform the following. Open the oil cooler hose clip located on the lower fan shroud. Remove the oil cooler hoses from the clip.
3. Raise and suitably support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
4. If equipped with RPO LY6 (6.0L) engine, remove the oil cooler hoses from the clip.
5. Place a jack or utility stands at the rear of the vehicle.
6. If equipped, remove the engine protection shield. Refer to «Engine Shield Replacement»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
7. If equipped remove the oil pan skid plate. Refer to. «Oil Pan Skid Plate Replacement (2500/3500 with RPO NZZ)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody)
8. For both 1500 and 2500 series, support the front differential carrier with a suitable adjustable jack.
9. For 1500 series vehicles, remove the differential carrier right side nuts.
10. Remove the differential carrier left side bolts.
11. Lower the differential carrier.
12. For 2500 series vehicles, remove the differential carrier right side nuts.
13. Remove the differential carrier upper mounting bolt and nut.
14. Remove the differential carrier lower mounting bolt and nut.
15. If equipped with RPO L76 (6.0L) engine, perform the following: Lower the differential carrier. Remove the oil cooler hose adapter bolts (2). Remove the oil cooler hose assembly and gasket. Discard the gasket. Inspect the fittings, connectors, and cooler hoses for damage or distortion.
16. If equipped with RPO LY6 (6.0L) engine, perform the following: Remove the oil cooler hose bracket bolt. (1) Remove the oil cooler hose adapter bolts. (2) Remove the oil cooler hose assembly. Discard the gasket. Inspect the fittings, connectors, and cooler hoses for damage or distortion.

1. If equipped with RPO LY6 (6.0L) engine, perform the following: Install the oil cooler hose assembly and a NEW gasket. Install the oil cooler hose adapter bolts (2). Tighten Tighten the bolts to 12 N.m (106 lb in). Install the oil cooler hose bracket bolt. Tighten Tighten the bolt to 25 N.m (18 lb ft).
2. If equipped with a RPO L76 (6.0L) engine, perform the following. Install the oil cooler hose assembly and a NEW gasket. Install the oil cooler hose adapter bolts (2). Tighten Tighten the bolts to 12 N.m (106 lb in). Install the oil cooler hose bracket bolt (1). Tighten Tighten the bolt to 25 N.m (18 lb ft).
3. For 2500 series vehicles, raise the differential carrier into position.
4. Install the differential carrier left side upper bolt and nut until snug.
5. Install the differential carrier left side lower bolt and nut until snug.
6. Install the differential carrier right side nuts. Tighten Tighten the bolt to 100 N.m (74 lb ft).
7. For 1500 series vehicles, raise the differential carrier into position.
8. Install the differential carrier right side nuts.
9. Install the differential carrier left side bolts. Tighten Tighten the bolts/nuts to 100 N.m (74 lb ft).
10. If equipped, install the engine protection shield. Refer to «Engine Shield Replacement»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
11. If equipped remove the oil pan skid plate. Refer to. «Oil Pan Skid Plate Replacement (2500/3500 with RPO NZZ)»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody)
12. Remove the jack or utility stand from the rear of the vehicle.
13. Lower the vehicle.
14. If equipped with RPO LY6 (6.0L) engine, install the oil cooler hoses to the clip.
15. If equipped with RPO L76 (6.0L) engine, perform the following: Install the oil cooler hoses to the hose clip on the fan shroud. Snap the oil cooler hose clip shut.
16. Install the oil cooler lines to the radiator. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

Fan Replacement (Mechanical)

Special Tools

1. J 41240-5A Fan Clutch Wrench
2. J-48460 Fan Clutch Remover and Installer Kit

1. Remove the upper fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Install the J-48460 Fan Clutch Remover and Installer Kit (1).
3. Install the J 41240-5A Fan Clutch Wrench (2).
4. Remove the fan hub nut from the water pump in a counterclockwise rotation.
5. Remove the fan clutch bolts from the rear of the fan blade.
6. Separate the fan clutch from the fan blade.

1. Install the fan clutch onto the fan blade.
2. Install the fan clutch bolts. Tighten Tighten the bolts to 23 (17 lb ft).
3. Install the fan assembly.
4. Install the J-48460 Fan Clutch Remover and Installer Kit (1) and J 41240-5A Fan Clutch Wrench (2). Tighten Tighten the nut clockwise to 56 (41 lb ft).
5. Install the upper fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

Fan Replacement (Diesel)

Special Tools

EN-46406-A Fan Clutch Remover and Installer

1. Remove the radiator air upper baffle. Refer to «Radiator Air Upper Baffle and Deflector Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the upper engine cooling fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Disconnect the electro-viscous fan clutch connector.
4. Use EN-46406-A fan clutch remover and installer to hold the water pump pulley and turn the fan hub nut counterclockwise to remove the fan clutch assembly.
5. Remove the 2 upper engine cooling fan shroud bolts (1).
6. Lift the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
7. Remove the engine shield. Refer to «Engine Shield Replacement»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
8. Remove the 2 lower engine cooling fan shroud bolts (1).
9. Lower the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
10. Remove the fan and clutch assembly, and the engine cooling fan shroud as an assembly.
11. Remove the fan and clutch assembly from the shroud.
12. Remove the fan clutch assembly nuts (1) from the rear of the fan blade (2).
13. Remove the fan clutch assembly (3) from the fan blade (2).

1. Install the fan clutch assembly (3) onto the fan blade (2).
2. Install the fan clutch assembly nuts (1) Tighten Tighten the nuts to 23 (17 lb ft).
3. Install the fan clutch assembly and the engine cooling fan shroud as an assembly onto the vehicle.
4. Install the 2 upper engine cooling fan shroud bolts (1) and loosely tighten the bolts.
5. Use EN-46406-A fan clutch remover and installer to hold the water pump pulley and turn the fan hub nut clockwise to install the fan and clutch assembly onto the water pump pulley. Tighten 56 (41 lb ft)
6. Lift the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
7. Install the 2 lower engine cooling fan shroud bolts (1) and loosely tighten the bolts.
8. Lower the vehicle.
9. Center the engine cooling fan shroud to the fan blade in 3 different locations (1) of the cooling fan shroud.
10. Make sure the orientation of the cooling fan shroud (1) and rubber seal (2) are installed correctly.
11. Tighten the 2 upper engine cooling fan shroud bolts (1). Tighten 8 (71 lb in)
12. Lift the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
13. Tighten the 2 lower engine cooling fan shroud bolts (1). Tighten 8 (71 lb in)
14. Install the engine shield. Refer to «Engine Shield Replacement»(/gmc/sierra-2500/2012-2012/remont/frames-subframes-crossmembers/#frame-and-underbody) .
15. Lower the vehicle.
16. Connect the electro-viscous fan clutch connector.
17. Install the upper engine cooling fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
18. Install the radiator air upper baffle assembly. Refer to «Radiator Air Upper Baffle and Deflector Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

Fan Clutch Replacement (Diesel)

Special Tools

J 41240-5A Fan Clutch Wrench

1. Remove the upper fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the 3 engine cooling fan shroud bolts (1).
3. Position the engine cooling fan shroud (1) forward to the radiator.
4. Install a long pin bar into the fan hub (1).
5. Use a J 41240-5A fan clutch wrench to remove the fan hub nut (2) from the hub in a counterclockwise rotation.
6. Remove the fan and the engine cooling fan shroud as an assembly.
7. Remove the fan clutch bolts from the rear of the fan blade.
8. Separate the fan clutch from the fan blade.

1. Install the fan clutch onto the fan blade.
2. Install the fan clutch bolts. Tighten Tighten the bolts to 23 (17 lb ft).
3. Install the fan and engine cooling fan shroud assembly to the fan hub.
4. Use a J 41240-5A fan clutch wrench on the fan clutch hub nut (2) to install a long pry bar to the fan clutch hub (1). Tighten Tighten the nut clockwise to 56 (41 lb ft).
5. Position the engine cooling fan shroud on the 3 mounting brackets (1).
6. Install the bolts. Loosely tighten the top mounting bolt at the oil filler neck.
7. Center the engine cooling fan shroud to the fan blade in 3 places (1).
8. Make sure the orientation of the cooling fan shroud (1) and rubber seal (2) are installed correctly
9. Fully tighten the 3 engine cooling fan shroud bolts (1). Tighten Tighten the bolts to 9 (80 lb in).
10. Install the upper fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Remove the drive belt. Refer to «Drive Belt Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) .
2. Remove the fan clutch. Refer to «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel) .
3. Disconnect the camshaft position (CMP) sensor electrical connector.
4. Remove the fan pulley bolts/nuts.
5. Remove the fan pulley.

1. Install the fan pulley.
2. Install the fan pulley bolts/nuts. Tighten Tighten the bolts/nuts to 41 N.m (30 lb ft).
3. Connect the CMP sensor electrical connector.
4. Install the fan clutch. Refer to «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel) .
5. Install the drive belt. Refer to «Drive Belt Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) .

1. Remove the cooling fan and shroud. Refer to «Cooling Fan and Shroud Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the cooling fan blade retainers.
3. Remove the cooling fan blades.

Note. The electric cooling fan assembly uses a 5-blade fan and a 7-blade fan. It does not matter which side the fan blades are installed on. DO NOT install two 5-blade assemblies or two 7-blade assemblies, as this would cause a noise issue.

1. Install the cooling fan blades.
2. Install the cooling fan blade retainers.
3. Install the cooling fan and shroud. Refer to «Cooling Fan and Shroud Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Remove the cooling blade(s). Refer to «Engine Coolant Fan Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the cooling fan motor bolts.
3. Remove the cooling fan motor(s).

1. Install the cooling fan motor(s).
2. Install the cooling fan motor bolts. Tighten Tighten the bolts to 10 N.m (89 lb in).
3. Install the cooling fan blades. Refer to «Engine Coolant Fan Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill)
2. Remove air inlet duct.
3. Disconnect upper radiator hose from radiator.
4. Disengage the radiator inlet hose clip (2) at the fan shroud.
5. If necessary, reposition the surge tank inlet hose clamp at the radiator.
6. If necessary, remove the surge tank inlet hose from the radiator.
7. Disconnect the electrical connectors from the cooling fans.
8. Remove the clip attaching the wiring harness to the shroud.
9. Remove transmission cooler lines bolts from fan shroud.
10. If necessary, open the engine oil cooler line clip and remove the cooler lines from the clip.
11. Remove the cooling fan shroud bolts.
12. Remove the cooling fan and shroud.

1. Install the cooling fan and shroud.
2. Install the cooling fan shroud bolts. Tighten Tighten the bolts to 9 N.m (80 lb in).
3. If equipped, install the cooler lines to the clip and close the clip.
4. Connect the electrical connectors to the cooling fans.
5. Install the clip attaching the wiring harness to the shroud.
6. Install the transmission cooling line bolts to fan shroud. Tighten Tighten the bolts to 4 N.m (35 lb in).
7. If necessary, install the surge tank inlet hose to the radiator.
8. If necessary, reposition the surge tank inlet hose clamp at the radiator.
9. Engage the radiator inlet hose clip (2) at the fan shroud.
10. Connect upper radiator hose from radiator.
11. Install air inlet duct.
12. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill)

Scheme 12

Engine Coolant Fan Resistor Replacement (Right HP2)

Scheme 13

Engine Coolant Fan Resistor Replacement (Left HP2)

Scheme 14

Turbocharger Coolant Hoses/Pipes Replacement (Feed-LGH/LML)

Scheme 15

Turbocharger Coolant Hoses/Pipes Replacement (Return to Turbocharger-LGH/LML)

1. Remove the cooling fan clutch. Refer to «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel) .
2. Remove the generator. Refer to «Generator Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system)
3. Remove the turbocharger. Refer to «Turbocharger Replacement (LGH)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) , «Turbocharger Replacement (LML)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) .
4. Remove the exhaust gas recirculation (EGR) cooler assembly. Refer to «Exhaust Gas Recirculation Valve Cooler Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Reposition the hose clamp and move the turbocharger coolant return hose (1) away from the turbocharger coolant return pipe (2).
6. Remove the turbocharger coolant return pipe retainer bolt(1).
7. Remove the turbocharger coolant return pipe retainer bolt (1) attached to the right front valve cover.
8. Remove the turbocharger coolant return pipe retainer bolt (1) on top of the engine.
9. Remove the turbocharger coolant return pipe (3)and hose (2) from the engine.
10. Replace any worn or damaged hoses.

1. Position the turbocharger coolant return pipe onto engine.
2. Install the turbocharger coolant return pipe retainer bolt (1). Tighten Tighten the bolt to 25 N.m (18 lb ft).
3. Install the turbocharger coolant return hose (2) onto the turbocharger coolant return pipe (2).
4. Install the turbocharger coolant return to the pipe retainer bolt (1) onto the right front valve cover. Tighten Tighten the bolt to 25 N.m (18 lb ft).
5. Install the turbocharger coolant return pipe retainer bolt (1). Tighten Tighten the bolt to 25 N.m (18 lb ft).
6. Install the turbocharger. Refer to «Turbocharger Replacement (LGH)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) , «Turbocharger Replacement (LML)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle)
7. Install the EGR cooler assembly. Refer to «Exhaust Gas Recirculation Valve Cooler Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
8. Install the generator. Refer to «Generator Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system)
9. Install the cooling fan clutch. Refer to «Fan Clutch Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement-diesel) .

Scheme 16

Exhaust Gas Recirculation Valve Cooler Replacement

Scheme 17

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (Cooler to Cooler Hose-LGH)

Scheme 18

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (Cooler to Cooler Hose-LML)

Scheme 19

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (EGR Manifold Return Hose-LGH, LML)

Scheme 20

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (Manifold Feed Pipe/Hose to Cooler-LGH)

Scheme 21

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (Manifold Feed Hose to Cooler-LML)

Scheme 22

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (EGR Bypass Pipe-LML)

Scheme 23

Exhaust Gas Recirculation Coolant Hoses/Pipes Replacement (Manifold Feed Pipe to Cooler Hose-LML)

Scheme 24

Exhaust Gas Recirculation Cooler Water Bypass Outlet Hose Replacement

1. Remove the air cleaner outlet resonator duct. Refer to «Air Cleaner Outlet Resonator Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-43l-repair-instructions) .
2. Remove the radiator inlet hose. Refer to «Radiator Inlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Radiator Inlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the water outlet bolts.
4. Remove the water outlet.
5. Remove and discard the gasket.

1. Install a NEW gasket to the water outlet.
2. Lubricate the O-ring seal with clean engine coolant.
3. Install the water outlet.
4. Install the water outlet bolts. Tighten Tighten the bolts to 25 N.m (18 lb ft).
5. Install the radiator inlet hose. Refer to «Radiator Inlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Radiator Inlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
6. Install the air cleaner outlet resonator duct. Refer to «Air Cleaner Outlet Resonator Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-43l-repair-instructions) .

1. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
2. Remove the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
3. Reposition the radiator outlet hose clamp at the water pump inlet.
4. Remove the radiator outlet hose from the water pump inlet.
5. Remove the water pump inlet bolts (1).
6. Remove the water pump inlet from the water pump.
7. Remove and discard the water pump inlet seal.

1. Install a NEW water pump inlet seal to the water pump inlet.
2. Position the water pump inlet to the water pump.
3. Install the water pump inlet bolts (1) and tighten to 15 N.m (11 lb ft).
4. Install the radiator outlet hose to the water pump inlet.
5. Position the radiator outlet hose clamp at the water pump inlet.
6. Install the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
7. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .

1. Remove the thermostat housing. Refer to «Engine Coolant Thermostat Housing Replacement (LFA, LH6, LMG, LY2, LY5, LY6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the thermostat.

1. Install the thermostat.
2. Install the thermostat housing. Refer to «Engine Coolant Thermostat Housing Replacement (LFA, LH6, LMG, LY2, LY5, LY6)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
2. Remove the upper fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the intake manifold tube. Refer to «Intake Manifold Tube Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) .
4. Remove the radiator inlet hose. Refer to «Radiator Inlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Radiator Inlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Disconnect the turbocharger coolant feed pipe retaining bracket bolt. Refer to «Turbocharger Coolant Hoses/Pipes Replacement (Feed-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Turbocharger Coolant Hoses/Pipes Replacement (Return to Bypass Pipe-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Turbocharger Coolant Hoses/Pipes Replacement (Return to Turbocharger-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
6. Remove the fuel pressure valve bracket bolts (1) and reposition the fuel pressure valve (2).
7. Remove the thermostat bolts (1) from the engine coolant outlet pipe (2).
8. Remove thermostat (1) and thermostat (2) from the thermostat housing.

Inspection Procedure

1. Inspect the thermostats for sticking, cracks, and/or leakage of wax.
2. Replace the thermostats if damage is found.
3. Clean the thermostat housing and thermostat housing cover sealing surfaces.

1. Install thermostat (1) and thermostat (2) with seals, to the thermostat housing.
2. Position the thermostat housing (2) and install the bolts (1). Tighten to 25 (18 lb ft).
3. Connect the turbocharger coolant feed pipe retaining bracket bolt. Refer to «Turbocharger Coolant Hoses/Pipes Replacement (Feed-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Turbocharger Coolant Hoses/Pipes Replacement (Return to Bypass Pipe-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Turbocharger Coolant Hoses/Pipes Replacement (Return to Turbocharger-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Position the fuel pressure valve (2) to the thermostat housing and tighten the bolts (1) to 25 (18 lb ft).
5. Connect the radiator inlet hose. Refer to «Radiator Inlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Radiator Inlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
6. Install the intake manifold tube. Refer to «Intake Manifold Tube Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) .
7. Connect the turbocharger coolant feed pipe retaining bracket bolt. Refer to «Turbocharger Coolant Hoses/Pipes Replacement (Feed-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Turbocharger Coolant Hoses/Pipes Replacement (Return to Bypass Pipe-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Turbocharger Coolant Hoses/Pipes Replacement (Return to Turbocharger-LGH/LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
8. Install the upper fan shroud. Refer to «Engine Coolant Fan Upper Shroud Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Engine Coolant Fan Upper Shroud Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
9. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .

1. Remove the radiator fan. Refer to «Fan Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement-mechanical) , «Fan Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement-diesel) .
2. Remove the radiator outlet hose. Refer to «Radiator Outlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__radiator-outlet-hose-replacement-lgh-lml) , «Radiator Outlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the drive belt tensioner. Refer to «Drive Belt Tensioner Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle) .
4. Remove the generator bracket. Refer to «Generator Bracket Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Bracket Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Bracket Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) .
5. Remove the air conditioning compressor bracket. Refer to «Air Conditioning Compressor Bracket Replacement (HP2)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) , «Air Conditioning Compressor Bracket Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) , «Air Conditioning Compressor Bracket Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
6. Remove the fuel pressure service valve bolt (1) and reposition the fuel pressure service valve (2).
7. Disconnect the engine coolant temperature sensor (1).
8. Remove the EGR manifold cooling return hose (2) and the turbocharger coolant feed hose (3).
9. Unclip the fuel return dampener (1) and set aside.
10. Remove the oil fill tube bolt (3); the oil fill tube retainer bracket bolt (2); the oil fill tube (5) and the seal (4).
11. Remove the turbocharger coolant return hose (1) from the turbocharger coolant return pipe (2).
12. Remove the bolts (2) from the thermostat bypass pipe (3).
13. Remove the thermostat housing crossover bolts (1) and nuts (2).
14. Remove the thermostat housing crossover pipe (4) and gaskets (3).

1. Position the thermostat housing crossover with NEW gaskets.
2. Install the thermostat housing crossover bolts (1) and nuts (2). Tighten to 25 N.m (18 lb ft).
3. Install the thermostat bypass bolts (2) to the water pump and tighten to 25 N.m (18 lb ft).
4. Connect the turbocharger coolant return hose (1) to the thermostat bypass pipe (3).
5. Clip the fuel return dampener (1) back into the retainer on top of the engine coolant outlet pipe.
6. Install the oil fill tube bolt (3) and tighten to 25 N.m (18 lb ft).
7. Install the oil fill tube bracket bolt (2) and tighten to 25 N.m (18 lb ft)
8. Install the EGR manifold cooling return hose (2); the turbocharger coolant feed hose (3) and the engine coolant temperature sensor connector (1).
9. Install the fuel pressure service valve bolts (1) and tighten to 25 N.m (18 lb ft)
10. Install the air conditioning bracket. Refer to «Air Conditioning Compressor Bracket Replacement (HP2)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) , «Air Conditioning Compressor Bracket Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) , «Air Conditioning Compressor Bracket Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
11. Install the generator bracket. Refer to «Generator Bracket Replacement (V6)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Bracket Replacement (V8)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) , «Generator Bracket Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/charging-system/#battery-charging-system-and-starting-system) .
12. Install the drive belt tensioner. Refer to «Drive Belt Tensioner Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle)
13. Install the radiator fan. Refer to «Fan Replacement (Mechanical)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement-mechanical) , «Fan Replacement (Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement-diesel) .

1. If replacing the rear coolant air bleed covers, remove the intake manifold. Refer to «Intake Manifold Replacement (Without AFM)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) , «Intake Manifold Replacement (With AFM)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) . Otherwise proceed to the next step.
2. Remove the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
3. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
4. Reposition the radiator vent inlet hose clamp (1) at the coolant air bleed pipe fitting.
5. Remove the radiator vent inlet hose (2) from the coolant air bleed pipe fitting.
6. Remove the coolant air bleed pipe bolts (309) (intake manifold shown removed for clarity).
7. Remove the coolant air bleed pipe (307) and seals (308).
8. Remove the coolant air bleed cover bolts (312), if required.
9. Remove the coolant air bleed covers (313) and seals (308), if required.
10. Remove the seals (308) from the coolant air bleed pipe and/or covers.
11. Discard the seals.

1. Install the seals onto the coolant air bleed pipe and/or covers.
2. Install the coolant air bleed pipe (307) and seals (308) onto the cylinder heads.
3. Install the coolant air bleed pipe bolts (309). Tighten Tighten the bolts to 12 N.m (106 lb in).
4. Install the coolant air bleed covers (313) and seals (308), if required.
5. Install the coolant air bleed cover bolts (312), if required. Tighten Tighten the bolts to 12 N.m (106 lb in).
6. Install the radiator vent inlet hose (2) to the coolant air bleed pipe fitting.
7. Position the radiator vent inlet hose clamp (1) at the coolant air bleed pipe fitting.
8. Install the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
9. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
10. If the rear coolant air bleed covers were replaced, install the intake manifold. Refer to «Intake Manifold Replacement (Without AFM)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) , «Intake Manifold Replacement (With AFM)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) .

1. Remove the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
2. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
3. Reposition the radiator vent inlet hose clamp (1) at the coolant air bleed pipe fitting.
4. Remove the radiator vent inlet hose (2) from the coolant air bleed pipe fitting.
5. Remove the coolant air bleed pipe bolts (309) (intake manifold shown removed for clarity).
6. Remove the coolant air bleed pipe (307) and seals (308).
7. Remove the coolant air bleed cover bolts (312), if required.
8. Discard the seals.

1. Install the seals onto the coolant air bleed pipe and/or covers.
2. Install the coolant air bleed pipe (307) and seals (308) onto the cylinder heads.
3. Install the coolant air bleed pipe bolts (309). Tighten Tighten the bolts to 12 N.m (106 lb in).
4. Install the coolant air bleed covers (313) and seals (308), if required.
5. Install the coolant air bleed cover bolts (312), if required. Tighten Tighten the bolts to 12 N.m (106 lb in).
6. Install the radiator vent inlet hose (2) to the coolant air bleed pipe fitting.
7. Position the radiator vent inlet hose clamp (1) at the coolant air bleed pipe fitting.
8. Install the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
9. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
10. If the rear coolant air bleed covers were replaced, install the intake manifold. Refer to «Intake Manifold Replacement (Without AFM)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) , «Intake Manifold Replacement (With AFM)»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) .

Scheme 25

Thermostat Bypass Pipe Replacement (LGH, LML)

Scheme 26

Heater Water Bypass Inlet Hose Replacement (EGR Bypass Valve to Cooler-LML)

Heater Water Bypass Inlet Hose Replacement (EGR Valve to Heater Hose-LML)

Heater Water Bypass Inlet Hose Replacement (EGR Valve to Heater Hose-LML)

1. Remove the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .
2. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
3. Reposition the radiator vent inlet hose clamp (1) at the coolant air bleed pipe fitting.
4. Remove the radiator vent inlet hose (2) from the coolant air bleed pipe fitting.
5. Reposition the radiator inlet hose clamp (3) at the water pump.
6. Remove the radiator inlet hose from the water pump.
7. Reposition the radiator inlet hose and vent inlet hose out of the way.
8. Remove the accessory drive belt. Refer to «Drive Belt Replacement - Accessory»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) .
9. Reposition the radiator outlet hose clamp at the water pump.
10. Remove the radiator outlet hose from the water pump.
11. Reposition the outlet hose out of the way.
12. Reposition the radiator surge tank outlet hose clamp at the water pump (1).
13. Remove the radiator surge tank outlet hose (2) from the water pump.
14. Reposition the outlet hose out of the way.
15. Reposition the heater inlet hose clamp (1) at the water pump.
16. Remove the heater inlet hose (2) from the water pump.
17. Reposition the inlet hose out of the way.
18. Remove the water pump bolts (301).
19. Remove the water pump (300) and gaskets (309). Discard the gaskets.

Note. All gaskets surfaces are to be free of oil or other foreign material during assembly.

1. Inspect the drained coolant for sand or other debris, flush the system as needed. Refer to «Flushing»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__flushing) .
2. Inspect and clear the radiator vent hose fitting, if necessary. There is a small 2.0 mm (0.080 in) orifice (vent hose fitting) in the neck of the radiator where the coolant vent hose from the engine attaches to the radiator.
3. Position the water pump (300) and NEW gaskets (306) to the engine block.
4. Install the water pump bolts (301). Tighten Tighten the bolts a first pass to 15 N.m (11 lb ft). Tighten the bolts a final pass to 30 N.m (22 lb ft).
5. Position and install the heater inlet hose (2) to the water pump.
6. Position the heater inlet hose clamp (1) at the water pump.
7. Position and install the radiator surge tank outlet hose (2) to the water pump.
8. Position the radiator surge tank outlet hose clamp at the water pump (1).
9. Position and install the radiator outlet hose to the water pump.
10. Position the radiator outlet hose clamp at the water pump.
11. Install the accessory drive belt. Refer to «Drive Belt Replacement - Accessory»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-48l-53l-60l-62l-repair-instructions-on-vehicle) .
12. Position the radiator inlet hose and vent inlet hose to the correct position.
13. Install the radiator inlet hose to the water pump.
14. Position the radiator inlet hose clamp (3) at the water pump.
15. Install the radiator vent inlet hose (2) to the coolant air bleed pipe fitting.
16. Position the radiator vent inlet hose clamp (1) at the coolant air bleed pipe fitting.
17. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
18. Install the air cleaner outlet duct. Refer to «Air Cleaner Resonator Outlet Duct Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-48l-53l-60l-62l-repair-instructions) .

1. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
2. Remove the fan pulley. Refer to «Fan Pulley Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the radiator outlet pipe. Refer to «Radiator Outlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__radiator-outlet-hose-replacement-lgh-lml) , «Radiator Outlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Remove the thermostat housing crossover. Refer to «Thermostat Housing Crossover Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Remove the crankshaft balancer. Refer to «Crankshaft Balancer Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle__crankshaft-balancer-replacement) .
6. Remove the water pump to water pump outlet pipe nuts (1) from the studs (2).
7. Remove the water pump nut (1) and bolts (2).
8. Remove the water pump (5).
9. Remove and discard the water pump O-ring (3) and the water pump outlet pipe gasket (4).

1. Lubricate the water pump O-ring (3) with engine oil.
2. Install the water pump outlet pipe gasket (4) and the lubricated water pump O-ring (3).
3. Install the water pump nut (1) and bolts (2). Ensure the correct length bolt is used in the proper location and tighten to 25 N.m (18 lb ft).
4. Install the water pump to water pump outlet pipe nuts (1) to the studs (2) and tighten to 25 N.m (18 lb ft).
5. Install the crankshaft balancer. Refer to «Crankshaft Balancer Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-66l-lgh-lml-repair-instructions-on-vehicle__crankshaft-balancer-replacement) .
6. Install the thermostat housing crossover. Refer to «Thermostat Housing Crossover Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
7. Install the fan pulley. Refer to «Fan Pulley Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
8. Install the radiator outlet pipe. Refer to «Radiator Outlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__radiator-outlet-hose-replacement-lgh-lml) , «Radiator Outlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
9. Perform the crankshaft position reluctor wheel learn procedure. Refer to «Crankshaft Position Reluctor Wheel Learn»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-66l-lgh-lml-repair-instructions) .

Water Pump Replacement (V6)

Special Tools

J 41240 Fan Clutch Remover and Installer

1. Remove the air cleaner outlet duct. Refer to «Air Cleaner Outlet Resonator Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-43l-repair-instructions) .
2. Remove the drive belt. Refer to «Drive Belt Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-43l) .
3. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
4. Reposition the radiator outlet hose clamps at the surge tank and water pump.
5. Remove the radiator outlet hose from the surge tank.
6. Remove the radiator outlet hose from the water pump.
7. Reposition the water pump inlet hose clamps.
8. Remove the water pump inlet hose.
9. Using J 41240 fan clutch remover and installer, hold the water pump pulley, remove the water pump pulley bolts.
10. Remove the water pump bolts.
11. Remove the water pump.
12. Remove and discard the water pump gaskets.
13. Clean and inspect the water pump for damage.

1. If reusing the old fasteners, apply sealant GM P/N 12346004, (Canadian P/N 10953480), or equivalent to the threads of the water pump bolts.
2. Install NEW water pump gaskets and the water pump.
3. Install the water pump bolts. Tighten Tighten the bolts to 45 (33 lb ft).
4. Using J 41240 fan clutch remover and installer, hold the water pump pulley, install the water pump pulley bolts. Tighten Tighten the bolts to 25 (18 lb ft).
5. Install the water pump inlet hose.
6. Position the water pump inlet hose clamps.
7. Install the radiator outlet hose to the water pump.
8. Install the radiator outlet hose to the surge tank.
9. Position the radiator outlet hose clamps at the surge tank and water pump.
10. Install the drive belt. Refer to «Drive Belt Replacement»(/gmc/sierra-2500/2012-2012/remont/mechanical/#engine-mechanical-43l) .
11. Install the air cleaner outlet duct. Refer to «Air Cleaner Outlet Resonator Replacement»(/gmc/sierra-2500/2012-2012/remont/testing-diagnostics/#engine-controlsfuel-43l-repair-instructions) .
12. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
13. Inspect the cooling system for leaks.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
2. If equipped with 4WD, remove the front differential. Refer to «Differential Carrier Assembly Replacement (2500 4WD)»(/gmc/sierra-2500/2012-2012/remont/differentials-drive-axles/#front-drive-axle) .
3. Remove the oil separator drain hose and pipe bracket bolt (5).
4. Remove the oil separator drain bolt (4) and reposition oil separator drain pipe (6).
5. Remove the water pump to water pump outlet pipe nuts (1) from the studs (2).
6. Remove the water pump to water pump outlet pipe studs (2) and discard the gasket (3).
7. Remove the water pump outlet pipe (1).
8. Remove and discard the water pump outlet pipe O-ring (2).

1. Install a NEW water pump outlet pipe O-ring (2) onto the pipe.
2. Lubricate the O-ring seal with engine coolant.
3. Position a NEW water pump outlet pipe gasket (3) to the water pump. Install the water pump to water pump outlet pipe studs (1) and tighten to 25 N.m (18 lb ft).
4. Install the water pump to water pump outlet pipe nuts (1) and tighten to 25 N.m (18 lb ft).
5. Install the oil separator drain pipe (6) with bolt (4) and the retainer bracket bolt (5).
6. If equipped with 4WD, install the front differential. Refer to «Differential Carrier Assembly Replacement (2500 4WD)»(/gmc/sierra-2500/2012-2012/remont/differentials-drive-axles/#front-drive-axle) .
7. Lower the vehicle.

1. Loosen the air cleaner outlet duct clamps from the throttle body.
2. Loosen the air cleaner outlet duct clamps from the mass airflow sensor (2).
3. Remove the air cleaner outlet duct.
4. If equipped remove the throttle body heater hose retainer from the fan shroud.
5. If equipped remove the inlet radiator hose retainer from the fan shroud.
6. Remove the fan shroud retainers.
7. Remove the fan shroud bolts
8. Remove the upper fan shroud.

1. Install the upper fan shroud.
2. Install the fan shroud bolts. Tighten Tighten the bolts to 9 N.m (80 lb in).
3. Install the fan shroud retainers.
4. If equipped install the inlet radiator hose retainer to the fan shroud
5. If equipped install the throttle body heater hose retainer to the fan shroud.
6. Install the air cleaner outlet duct.
7. Tighten the air cleaner outlet duct clamp at the throttle body. Tighten Tighten the clamp to 4 N.m (35 lb in).
8. Tighten the air cleaner outlet duct clamp at the mass airflow sensor (2). Tighten Tighten the clamp to 4 N.m (35 lb in).

1. Remove the air cleaner outlet duct.
2. Remove the A/C line retainer from the fan shroud.
3. Remove the transmission control module (TCM) retainer (1).
4. Remove TCM from the fan shroud and reposition.
5. Remove the fan shroud retainers (1).
6. Remove the fan shroud bolts (2).
7. Remove the upper fan shroud.

1. Install the upper fan shroud.
2. Install the fan shroud retainers (1).
3. Install the fan shroud bolts (2). Tighten Tighten the bolts to 9 N.m (80 lb in).
4. Install the transmission control module (TCM) (2).
5. Install the transmission control module (TCM) retainer (1).
6. Install the A/C line retainer to the fan shroud.
7. Install the air cleaner outlet duct.

1. Remove the radiator. Refer to «Radiator Replacement (4.3L, 4.8L, 5.3L, and 6.0L)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Radiator Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Disengage the two clips from the radiator.
3. If equipped with engine oil cooler, remove the oil cooler hose clip from the lower fan shroud.
4. Remove the shroud from the vehicle.

1. Install the lower fan shroud and ensure it is centered over lower radiator support.
2. Engage the two clips from the radiator.
3. If equipped with the engine oil cooler, Install the oil cooler hose clip to the lower fan shroud.
4. Install the radiator. Refer to «Radiator Replacement (4.3L, 4.8L, 5.3L, and 6.0L)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) , «Radiator Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Remove the cooling fan and shroud. Refer to «Cooling Fan and Shroud Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the radiator outlet hose for the 4.3L engine, or the 4.8L, 5.3L and 6.0L engines. Refer to «Radiator Outlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__radiator-outlet-hose-replacement-lgh-lml) , «Radiator Outlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Disconnect the engine oil cooler lines from the radiator, If Equipped. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Disconnect the transmission oil cooler lines from the radiator, If Equipped. Refer to «Transmission Fluid Cooler Hose/Pipe Quick-Connect Fitting Disconnection and Connection»(/gmc/sierra-2500/2012-2012/remont/automatic-trans/#automatic-transmission-4l60-e-repair-instructions-on-vehicle) .
5. Remove the radiator bolts.
6. Remove the radiator.

1. Install the radiator.
2. Install the radiator bolts. Tighten Tighten the bolts to 25 N.m (18 lb ft).
3. Connect the transmission oil cooler lines to the radiator, If Equipped. Refer to «Transmission Fluid Cooler Hose/Pipe Quick-Connect Fitting Disconnection and Connection»(/gmc/sierra-2500/2012-2012/remont/automatic-trans/#automatic-transmission-4l60-e-repair-instructions-on-vehicle) .
4. Connect the engine oil cooler lines to the radiator, If Equipped. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting Replacement»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Install the radiator outlet hose for the 4.3L engine, or the 4.8L, 5.3L and 6.0L engines. Refer to «Radiator Outlet Hose Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__radiator-outlet-hose-replacement-lgh-lml) , «Radiator Outlet Hose Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .
6. Install the cooling fan and shroud. Refer to «Cooling Fan and Shroud Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system) .

Scheme 27

Radiator Replacement (LGH, LML)

1. Remove the radiator air upper baffle retainers (Qty 8).
2. Remove the radiator air upper baffle.

1. Install the radiator air upper baffle.
2. Install the radiator air upper baffle retainers (Qty 8).

1. Drain the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
2. Disconnect the heater cord from the coolant heater (4).
3. Loosen the coolant heater bolt.
4. Remove the coolant heater from the engine block.
5. Do not score the machined surface of the hole.
6. Grasp the plug with pliers.
7. Pull the plug from the engine block.
8. Clean the core plug hole in order to remove the following substances: Burrs Compound Paint Rough spots

1. Coat the O-ring seal and the cleaned surface of the plug opening with water resistant high-temperature grease lubricant GM P/N 9985164 (Canadian P/N 10953480), or the equivalent.
2. Tightly push the coolant heater (1) into the engine block.
3. Tighten the coolant heater bolt until both of the locking wings draw tightly against the inner wall of the engine block. Tighten the bolt to 2 N.m (18 lb in).
4. Connect the heater cord to the coolant heater (4).
5. Fill the cooling system. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
6. Inspect the cooling system for leaks.

1. Drain the cooling system/engine block. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .
2. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
3. For 1500 series vehicles, remove the oil pan skid plate bolts and plate, if equipped.
4. For 2500 series vehicle, remove the front 2 oil pan skid plate bolts, loosen the 2 rear bolts and remove the skid plate, if equipped.
5. For vehicles with regular production option (RPO) LY6 (6.0L) perform the following steps otherwise proceed to step 10.
6. Remove the oil cooler hose bracket bolt (1).
7. Remove the oil cooler hose adapter bolts (2).
8. Remove and discard the oil cooler hose adapter gasket.
9. Reposition the oil cooler hose adapter end out of the way.
10. Disconnect the coolant heater cord electrical connector.
11. Remove the coolant heater from the engine block.
12. Remove any burrs, sealer, or other rough spots.

1. If reusing the old coolant heater, apply thread sealant GM P/N 12346004 (Canadian P/N 10953480), or equivalent to the threads.
2. Install the coolant heater to the engine block and tighten to 50 N.m (37 lb ft).
3. Connect the coolant heater cord electrical connector.
4. For vehicles with RPO LY6 (6.0L) perform the following steps otherwise proceed to step 9.
5. Position the oil cooler hose adapter end.
6. Install a NEW oil cooler hose adapter gasket.
7. Install the oil cooler hose adapter bolts (2) and tighten to 12 N.m (106 lb in).
8. Install the oil cooler hose bracket bolt (1) and tighten to 25 N.m (18 lb ft).
9. If applicable, for 2500 series vehicles, position the oil pan skid plate and install the 2 front bolts and tighten the 2 rear bolts and tighten to 20 N.m (15 lb ft).
10. If applicable, for 1500 series vehicles position and install the oil pan skid plate and bolts and tighten to 20 N.m (15 lb ft).
11. Lower the vehicle.
12. Fill the cooling system/engine block. Refer to «Cooling System Draining and Filling (Vac-N-Fill Gasoline)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) , «Cooling System Draining and Filling (Static Fill)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Static Fill LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-static) , «Cooling System Draining and Filling (Vac-N-Fill Diesel)»(/gmc/sierra-2500/2012-2012/remont/cooling-system-mechanical/#engine-cooling-system__cooling-system-draining-and-filling-vac-n-fill) .

Scheme 28

Coolant Heater Replacement (Diesel)

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
2. Remove the oil pan skid plate bolts and plate, if equipped.
3. Disconnect the coolant heater cord electrical connector.
4. Remove the coolant heater cord retainer (5) from the frame.
5. Remove the coolant heater cord clip (6) from the front brake front pipe.
6. Lower the vehicle.
7. Remove the coolant heater cord bolt (4) from the frame.
8. Remove the coolant heater cord clip (2) from the chassis harness.
9. Remove the coolant heater cord clip (1) from the front spring stud.
10. Remove the coolant heater cord from the vehicle.

1. Install the coolant heater cord to the vehicle.
2. Install the coolant heater cord clip (1) to the front spring stud.
3. Install the coolant heater cord clip (2) to the chassis harness.
4. Position the coolant heater cord clip to the frame and install the coolant heater cord bolt (4). Tighten Tighten the bolt to 8 N.m (71 lb in).
5. Raise the vehicle.
6. Install the coolant heater cord clip (6) to the front brake front pipe.
7. Position the coolant heater cord clip to the frame and install the coolant heater cord retainer (5).
8. Connect the coolant heater cord electrical connector.
9. Position and install the oil pan skid plate and bolts, if equipped. Tighten Tighten the bolts to 20 N.m (15 lb ft).
10. Lower the vehicle.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
2. Remove the front 2 oil pan skid plate bolts, loosen the 2 rear bolts and remove the skid plate, if equipped.
3. Disconnect the coolant heater cord electrical connector.
4. Remove the coolant heater cord clip (1) from the front brake front pipes.
5. Remove the coolant heater cord clip retainer (2) from the frame.
6. Lower the vehicle.
7. Remove the coolant heater cord bolt (3) from the frame.
8. Remove the coolant heater cord from the vehicle.

1. Install the coolant heater cord to the vehicle.
2. Position the coolant heater cord clip to the frame and install the coolant heater cord bolt (3). Tighten Tighten the bolt to 8 N.m (71 lb in).
3. Raise the vehicle.
4. Install the coolant heater cord clip retainer (2) to the frame.
5. Install the coolant heater cord clip (1) to the front brake front pipes.
6. Connect the coolant heater cord electrical connector.
7. Position the oil pan skid plate and install the 2 front bolts and tighten the 2 rear bolts, if equipped. Tighten Tighten the bolts to 20 N.m (15 lb ft).
8. Lower the vehicle.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#general-information__lifting-and-jacking-the-vehicle) .
2. Remove the oil pan skid plate bolts and plate, if equipped.
3. Disconnect the coolant heater cord electrical connector.
4. Remove the coolant heater cord clip (3) from the engine harness channel.
5. Remove the coolant heater cord clip (1) from the power steering gear outlet hose.
6. Lower the vehicle.
7. Remove the coolant heater cord bolt (2) from the frame.
8. Remove the coolant heater cord from the vehicle.

1. Install the coolant heater cord to the vehicle.
2. Position the coolant heater cord clip to the frame and install the coolant heater cord bolt (2). Tighten Tighten the bolt to 8 N.m (71 lb in).
3. Raise the vehicle.
4. Install the coolant heater cord clip (1) to the power steering gear outlet hose.
5. Install the coolant heater cord clip (3) to the engine harness channel.
6. Connect the coolant heater cord electrical connector.
7. Position and install the oil pan skid plate and bolts, if equipped. Tighten Tighten the bolts to 20 N.m (15 lb ft).
8. Lower the vehicle.

Scheme 29

Coolant Heater Cord Replacement (LGH/LML)

Cooling Fan Control w/o HP2

System Overview

The engine cooling fan system consists of 2 electric cooling fans and 3 fan relays. The cooling fan relays are arranged in a series/parallel (S/P) configuration. This allows the engine control module (ECM) to operate both fans together at low or high speeds using 2 fan control circuits. The cooling fans receive positive voltage from the cooling fan relays, which receive battery positive voltage from the underhood fuse block. The cooling fans are supplied a ground at G100 and G101.

Low Speed Operation

The ECM applies ground to the coil side of the cooling fan low speed relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low speed relay. The left cooling fan is connected in series to the right cooling fan through the de-energized series/parallel (S/P) cooling fan speed control relay. The result is a series circuit that operates both fans at low speed.

High Speed Operation

The ECM applies a ground to the coil side of the cooling fan low speed relay, the S/P cooling fan speed control relay, and the cooling fan high speed relay. When energized, the high speed fan relay applies voltage directly to the right cooling fan through the switch side of the relay. Simultaneously, the low speed fan relay and the S/P speed control relay provide ignition voltage and a direct path to ground for the left cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans operating at high speed.

Cooling Fan Control w/ HP2

System Overview

The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.

Low Speed Operation

The ECM applies a ground to the fan 1 control circuit for the low fan relay. This energizes the low fan relay coil, closes the relay contacts, and supplies battery positive voltage from the fan 1 fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the de-energized fan control relay, through the right cooling fan in-line resistor, and right cooling fan. The result is a series circuit with both fans running at a reduced speed.

Medium Speed Operation

The ECM applies a ground to the fan 2 control circuit, which energizes a bank of three relays consisting of the FAN Mid 1 relay, the fan control relay, and the FAN Mid 2 relay. When these three relays are energized the Mid 1 relay supplies battery voltage to the left cooling fan through the left cooling fan resistor. A direct ground path is provided for the left fan through the energized fan control relay. At the same time the Mid 2 relay is energized which applies battery voltage to the right cooling fan through the right cooling fan resistor. The result is a parallel circuit where each fan has voltage applied through a separate resistor, causing each fan to operate at a medium speed.

High Speed Operation

The ECM applies a ground to the fan 1, fan 2, and fan 3 relay control circuits simultaneously, which activates all five relays. This allows battery voltage to be applied directly to the right cooling fan from the Fan High relay, and battery voltage to be applied directly to the left fan from the Fan Low relay. The left fan is supplied a direct path to ground through the energized fan control relay. This arrangement provides each fan with direct battery voltage and its own ground path. The result is a parallel circuit with both fans running at full speed. When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage.

Cooling Fan Control

The purpose of the electro-viscous (EV) fan clutch is to maintain powertrain cooling requirements. The engine control module (ECM) monitors the following sensors to regulate the fan speed

1. Engine coolant temperature sensor
2. A/C refrigerant pressure sensor
3. Vehicle speed sensor
4. Intake air temperature sensor
5. Transmission fluid temperature sensor
6. Ambient air temperature sensor
7. Cooling fan speed sensor

The ECM controls the EV fan clutch operation. The ECM regulates a 12-volt pulse width modulated signal (PWM) to the cooling fan relay. The PWM signal determines the ON time of the relay. As the ECM command increases, so does the ON time of the relay. The relay ON time directly controls the amount of time the solenoid, which is internal to the fan clutch, is energized. When the solenoid in the fan clutch is energized, it opens the spring loaded valve and allows fluid to flow from the storage chamber to the fluid coupling of the cooling fan clutch, which increases the fan speed. When the solenoid is de-energized, the spring loaded valve closes, and allows the fluid in the coupling of the fan clutch to drain back to the storage chamber, which reduces fan speed. The rapid modulation of the fan clutch solenoid valve gives the ECM the ability to precisely control the amount of fluid that remains in the fluid coupler, allowing more effective regulation of the fan speed and powertrain cooling requirements.

The fan clutch supplies a feedback signal to the ECM, as an actual fan speed input. The fan speed sensor is a hall effect sensor which is internal to the fan clutch. The ECM supplies a 5-volt reference and a low reference to the hall effect sensor. The hall effect sensor returns a signal pulse through the cooling fan speed signal circuit in response to the reluctor track passing by the magnetic field of the hall effect sensor.

The scan tool can operate the cooling fan clutch. This is done through the controls function menu screen. Cooling fan clutch engagement can take up to 2 minutes with a 100 percent command and the engine speed at 2, 000 RPM. The lower the engine speed, the longer it will take for the fan to engage. Cooling fan disengagement can take up to 2 minutes with the engine speed at 2, 000 RPM. The lower the engine speed, the longer it will take to disengage. In lower ambient air temperatures the cooling fan will engage in less time, however, it will take longer to disengage due to the properties of the fluid vs. temperature.

Under certain conditions the cooling fan may be engaged at engine start. The cooling may have been engaged at the time the engine was turned off. Or, fluid may bleed from the storage chamber into the fluid coupling of the cooling fan clutch while the engine is off. Although the fan clutch is commanded off during a cold start, this is the most likely time a vehicle driver will notice that the fan noise is excessive in comparison to engine starts when the fan clutch is disengaged.

Engine Coolant Indicators

ENGINE COOLANT HOT

The instrument panel cluster (IPC) displays ENGINE COOLANT HOT message when the IPC receives a class 2 message from the powertrain control module (PCM) requesting illumination of this driver warning.

ENGINE OVERHEATED

The IPC displays ENGINE OVERHEATED message when the IPC receives a class 2 message from the PCM requesting illumination of this driver warning.

LOW COOLANT LEVEL B

The IPC displays LOW COOLANT LEVEL message when the IPC receives a class 2 message from the PCM requesting illumination of this driver warning.

REDUCED ENGINE POWER

The IPC displays REDUCED ENGINE POWER message when the IPC detects a reduced engine power condition from the PCM. The IPC receives a class 2 message from the PCM requesting illumination when the engine temperature exceeds a calibrated value.

Cooling Fan Control - Two Fan System

The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

The PCM commands the low speed cooling fans ON under the following conditions

1. Engine coolant temperature exceeds a calibrated value.
2. A/C refrigerant pressure exceeds a calibrated value.
3. After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 101°C (214°F) the low speed fans will run for a minimum of 60 seconds After 60 seconds, if the coolant temperature drops below 101°C (214°F) the fans will shut OFF. The fans will automatically shut OFF after 3 min. regardless of coolant temperature.

The PCM commands the high speed fans ON under the following conditions

1. Engine coolant temperature exceeds a calibrated value.
2. A/C refrigerant pressure exceeds a calibrated value.
3. When certain DTCs set.

At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed if required. This insures idle stability by preventing the fans from cycling between high and low speed.

Coolant Level Control (If Equipped)

The engine cooling system contains an engine coolant level switch to alert the driver in the event of a coolant loss. The powertrain control module (PCM) sends out a coolant loss signal over the coolant level switch signal circuit. When the engine coolant level switch reads a low coolant level in the fill tank, the switch opens. The message center receives its power from engine wiring harness junction block on the battery positive voltage circuit. Ground is provided by the ground circuits via the body wiring harness junction block and the engine wiring harness junction block. The cluster receives the class 2 message from the PCM indicating Low Coolant and displays the LOW COOLANT LEVEL message on the driver information center (DIC).

Coolant Heater

The optional engine coolant heater (RPO K05) operates using 110-volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather -18°C (0°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the plug when not in use.

Auxiliary Coolant Pump (w/HP2)

The auxiliary coolant pump circulates coolant through the engine and heater core when HVAC requires heating and the engine is HOT and OFF. The hybrid control module (HCM) will turn on the auxiliary coolant pump when the HVAC control module commands it to do so by sending a class 2 signal to the HCM.

The cooling system's function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly.

Cooling Cycle

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Coolant will then be pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders, where it absorbs heat.

Some coolant is also pumped from the water pump to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the throttle body. There it circulates through passages in the casting. During initial start up, the coolant assists in warming the throttle body. During normal operating temperatures, the coolant assists in regulating the throttle body temperature.

Cooling Cycle (6.6L Diesel Engine)

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. The coolant flows to the heater core while the engine is running. This provides the passenger compartment with heat and defrost.

Coolant is then pumped through the water pump outlet and through the coolant pipe to the engine oil cooler. The coolant flows around the oil cooler element and to the rear engine cover. The rear engine cover distributes the coolant flow to both banks of the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the turbocharger. There it circulates through passages in the center housing. During engine warm-up cycle the bypass valve located in the turbocharger inlet hose at the outlet pipe prevents coolant flow. During normal operating temperatures, the coolant assists in keeping the turbocharger cool.

From the cylinder heads, the coolant flows to the thermostats. The coolant flows from the thermostat housing to the water pump through the bypass pipe until the engine reaches 85°C (185°F).

Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components

Coolant

The engine coolant is a solution made up of a 50-50 mixture of DEX-COOL and suitable drinking water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere.

Radiator

The radiator is a heat exchanger. It consists of a core and two tanks. The aluminum core is a tube and fin crossflow design that extends from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer to the atmosphere.

The inlet and outlet tanks are a molded, high temperature, nylon reinforced plastic material. A high temperature rubber gasket seals the tank flange edge to the aluminum core. The tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core.

The radiator also has a drain cock located in the bottom of the left hand tank. The drain cock unit includes the drain cock and drain cock seal.

The radiator removes heat from the coolant passing through it. The fins on the core transfer heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.

Surge Tank

The surge tank is a plastic tank with a threaded pressure cap. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system that allows the coolant to expand and contract. The surge tank provides a coolant fill point and a central air bleed location.

During vehicle use, the coolant heats and expands. The increased coolant volume flows into the surge tank. As the coolant circulates, any air is allowed to bubble out. Coolant without air bubbles absorbs heat much better than coolant with bubbles.

Surge Tank (6.6L Diesel Engine)

This surge tank is actually two chambers connected together, (a surge tank and an overflow bottle). The front chamber (closest to the engine) is the surge tank and is the highest point of the coolant system. It uses a threaded pressure cap, similar to the one used on a radiator or engine fill system. The rear chamber (closest to the fender) is the overflow bottle. This is the air space in the cooling system where the coolant can expand into and contract from.

During vehicle use, the coolant heats and expands. The increased coolant volume can in some conditions push past the pressure cap and through a channel into the overflow bottle. As the coolant circulates, air is allowed to bubble out. This air is then transferred to the overflow bottle, through the surge tank cap, where it returns to the atmosphere. Coolant without air bubbles absorbs heat much better than coolant with bubbles. When the engine cools, the coolant, without air bubbles, contracts back into the surge tank from the bottom of the overflow bottle.

Pressure Cap

The pressure cap seals the cooling system. It contains a blow off or pressure relief valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring, which protects the radiator from excessive cooling system pressure. The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, might cause the radiator and/or coolant hoses to collapse.

The pressure cap allows cooling system pressure to build up as the temperature increases. As the pressure builds, the boiling point of the coolant increases. Engine coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat transfers from the radiator to the cooler, passing air.

The pressure in the cooling system can get too high. When the cooling system pressure exceeds the rating of the pressure cap, it raises the pressure valve, venting the excess pressure.

As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the surge tank. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator and coolant hoses from collapsing.

Cooling Fan and Clutch

The engine cooling fan and clutch are driven by the crankshaft via the drive belt. The cooling fan draws air through the radiator to improve the transfer of heat from the coolant to the atmosphere. As the fan blades spin, they pull cool, outside air past the radiator core. The fan clutch drives the cooling fan. The fan clutch controls the amount of torque that is transmitted from the crankshaft to the fan blades. The clutch allows more torque to engage on the fan when the engine operating temperature increases and/or the vehicle speed is low. As the torque increases, the fan turns more quickly. The fan clutch decreases the torque applied to the cooling fan when the engine temperature decreases and/or the vehicle speed is high. As the torque decreases, the fan speed decreases.

Air Baffles and Seals

The cooling system uses deflectors, air baffles and air seals to increase cooling system capability. Deflectors are installed under the vehicle to redirect airflow beneath the vehicle and through the radiator to increase engine cooling. Air baffles are also used to direct airflow through the radiator and increase cooling capability. Air seals prevent air from bypassing the radiator and A/C condenser, and prevent recirculation of hot air for better hot weather cooling and A/C condenser performance.

Special Tools

Illustration Tool Number/Description GE 47716 Vac-N-Fill Coolant Refill Tool J 24460-1 Cooling System Pressure Tester J 24731 Tempil Stick J 26568 Coolant and Battery Fluid Tester J 38185 Hose Clamp Pliers J 41240 or J 46406-A Fan Clutch Remover and Installer Kit includes (36mm) Wrench J 41240-2 Fan Clutch Wrench (36mm) J 41240-5A Fan Clutch Wrench (47mm) J 42401 Radiator Cap/Surge Tank Test Adapter J 43244 Relay Puller Pliers J 46406-1 Fan Clutch Remover and Installer

Scheme 30

Scheme 31

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Scheme 33

Scheme 34

Scheme 35

Scheme 36

Scheme 37

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Control Module References
• Diagnostic Repair Verification
• Electrical Center Identification Views
• Relay Replacement (Within an Electrical Center)
• Relay Replacement (Attached to Wire Harness)
• Diagnostic Trouble Code (DTC) List - Vehicle
• DTC P0641, P0651, P0697, P06A3, P06D2, or P06D6
• Instrument Cluster Description and Operation
• Audible Warnings Description and Operation
• Coolant in Combustion Chamber
• Coolant in Engine Oil
• Hybrid Modes of Operation Description
• Engine Coolant Temperature Sensor Replacement
• Engine Oil and Oil Filter Replacement
• Engine Coolant/Water in Transmission
• Lifting and Jacking the Vehicle
• Fastener Caution
• Approximate Fluid Capacities
• Front Wheelhouse Liner Replacement - Right Side (GMC)
• Air Cleaner Assembly Replacement
• Special Tools
• Oil Filler Tube Replacement
• Air Cleaner Assembly Replacement
• Generator Replacement (Diesel)
• Hot Exhaust System Warning
• Exhaust Pipe Heat Shield Replacement (Exhaust Manifold Outlet Pipe-Left)
• Air Cleaner Outlet Resonator Replacement
• Crankshaft Balancer Replacement
• Drive Belt Replacement
• Differential Carrier Assembly Replacement (2500 4WD)
• Transmission Fluid Cooler Hose/Pipe Quick-Connect Fitting Disconnection and Connection
• Transmission Fluid Cooler Hose/Pipe Replacement
• DTC P0480 (LGH/LML)
• Fan Clutch Replacement (Diesel)
• Cooling System Draining and Filling (Vac-N-Fill Gasoline)
• Cooling System Draining and Filling (Static Fill)
• Thermostat Diagnosis
• Engine Overheating
• Water Pump Replacement (V6)
• Loss of Coolant
• Engine Fails To Reach Normal Operating Temperature
• Fan Clutch Diagnosis
• Cooling System Leak Testing
• Pressure Cap Testing
• Fastener Tightening Specifications
• Fan Replacement (Mechanical)
• Fan Replacement (Diesel)
• Flushing
• Special Tools
• Engine Oil Cooler Hose/Pipe Quick-Connect Fitting Disconnection and Connection
• Radiator Outlet Hose Replacement (LGH, LML)