• Perform the Diagnostic System Check prior to using this diagnostic procedure:Diagnostic System Check - Vehicle
• Review the description of Strategy Based Diagnosis:Strategy Based Diagnosis
• An overview of each diagnostic category can be found here:Diagnostic Procedure Instructions

For an overview of the component/system, refer to:Cooling System Description and Operation

• DTCs related to the following system/component = Not Set
• B34 Engine Coolant Temperature Sensor
• B66 Intake Air Temperature Sensor
• B75C Multifunction Intake Air Sensor
• Engine Off Time=For greater than 30 min
• Engine Run Time=30 s to 30 min
• Fuel Alcohol Content=Less than 87%
• Start-Up ECT=−40 to 52°C (−40 to 126°F)

Frequency the DTC runs=Once—Per ignition cycle—After the running conditions are met

Engine Coolant Temperature=Not within a calibrated range

DTCs listed in the DTC Descriptor category=Type B DTC

• A/C Compressor=Off
• Cooling Fan=On
• Engine Coolant Temperature—Gauge=Inoperative

DTCs listed in the DTC Descriptor category=Type B DTC

The parameters for intake air temperature and engine coolant temperature should be within 3°C (5°F) of each other if the ignition has been Off for greater than 8 h.

High resistance in the circuits of the component may set DTC P0128 without setting the DTC for the component:B34 Engine Coolant Temperature Sensor

Engine Controls Schematics

Master Electrical Component List

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Control Module References

1. Verify the condition does not exist:Incorrect fluid level or condition»Refer to:Loss of Coolant
• If a condition exists

  Repair or replace as necessary

• If no condition exists
2. Verify there are no DTCs set related to the following component/system:B34 Engine Coolant Temperature Sensor
• If a related DTC is set

  Refer to:Diagnostic Trouble Code (DTC) List - Vehicle

• If a related DTC is not set
3. Engine»Running@1,800 to 2,200 RPM

   Verify the scan tool parameter:ECT Sensor=Greater than 80°C (176°F)—Within 15 min

• If 80°C (176°F) or colder

  Test or replace the component:Engine Coolant Thermostat

• If warmer than 80°C (176°F)
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

   Verify the DTC does not set.

• If the DTC sets

  Refer to: Circuit/System Testing

• If the DTC does not set
5. All OK.

Note: It may take up to 2 min for all vehicle systems to power down before an accurate ground or low reference circuit continuity test can be performed.

1. Ignition/Vehicle & All vehicle systems » Off
2. Disconnect the electrical connector:B34 Engine Coolant Temperature Sensor
3. Test for less than 10 Ω between the test points:Low Reference circuit terminal 1&Ground
• If 10 Ω or greater
1. Disconnect the appropriate electrical connector:X2@K20 Engine Control Module
2. Test for less than 2 Ω between the test points:Low Reference circuit terminal 1@Component harness&Terminal 2 X2@Control module harness
• If 2 Ω or greater » Repair the open/high resistance in the circuit.
• If less than 2 Ω » Replace the component:K20 Engine Control Module
• If less than 10 Ω
4. Ignition » On / Vehicle » In Service Mode
5. Verify the scan tool parameter:ECT Sensor=Colder than −39°C (−38°F)
• If −39°C (−38°F) or warmer
1. Ignition/Vehicle » Off
2. Disconnect the appropriate electrical connector:X2@K20 Engine Control Module
3. Test for infinite resistance between the test points:Signal circuit terminal 2@Component harness&Ground
• If less than infinite resistance » Repair the short to ground on the circuit.
• If infinite resistance » Replace the component:K20 Engine Control Module
• If colder than −39°C (−38°F)
6. Connect a 3 A fused jumper wire between the test points:Signal circuit terminal 2&Low Reference circuit terminal 1
7. Verify the scan tool parameter:ECT Sensor=Warmer than 149°C (300°F)
• If 149°C (300°F) or colder
1. Ignition/Vehicle » Off & Remove » Jumper wire(s)
2. Disconnect the appropriate electrical connector:K20 Engine Control Module
3. Ignition » On / Vehicle » In Service Mode
4. Test for less than 1 V between the test points:Signal circuit terminal 2@Component harness&Ground
• If 1 V or greater » Repair the short to voltage on the circuit.
• If less than 1 V
5. Ignition/Vehicle » Off
6. Test for less than 2 Ω between the test points:Signal circuit terminal 2@Component harness&Terminal 43 X2@Control module harness
• If 2 Ω or greater » Repair the open/high resistance in the circuit.
• If less than 2 Ω » Replace the component:K20 Engine Control Module
• If warmer than 149°C (300°F)
8. Test or replace the component:B34 Engine Coolant Temperature Sensor

1. Ignition/Vehicle » Off
2. Disconnect the electrical connector:B34 Engine Coolant Temperature Sensor
3. Test the resistance between the test points:Signal circuit terminal 2&Low Reference circuit terminal 1
4. Verify the value is within the range listed in the table:Temperature Versus Resistance - Engine Coolant Temperature Sensor
• If not in the specified range

  Replace the component:B34 Engine Coolant Temperature Sensor

• If in the specified range
5. Test for infinite resistance between the test points:Each terminal of the component&The component's housing
• If less than infinite resistance

  Replace the component:B34 Engine Coolant Temperature Sensor

• If infinite resistance
6. All OK.

Perform the Diagnostic Repair Verification after completing the repair:Diagnostic Repair Verification

• Engine Coolant Temperature Sensor Replacement
• For control module replacement, programming, and setup refer to:Control Module References