2010 Cadillac Truck Escalade/ESV RWD V8-6.2L Page 1783
Diagnostic Aids
* DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation.
* DTC P0128 occurring causes the Engine Coolant Temperature Gage to default to cold.
* Inspect the ECT sensor terminals and the ECT harness connector for corrosion. This condition results in a greater voltage on the ECT sensor
signal circuit, which is interpreted by the ECM as a colder ECT.
* This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures between -7 to
+80掳C (+19 to +176掳F), then compare those measurements to the Temperature Versus Resistance (See: Powertrain Management/Computers
and Control Systems/Specifications/Temperature Versus Resistance) table.
* A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a
greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.
Reference Information
Schematic Reference
Engine Controls Schematics (See: Diagrams/Electrical Diagrams/Powertrain Management/System Diagram)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Electrical Information Reference
* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit
Testing/Circuit Testing)
* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic
Procedures/Connector Repairs/Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General
Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring
Repairs/Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (See: Diagnostic Trouble Code Descriptions/Powertrain Diagnostic Trouble Code
(DTC) Type Definitions)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Cooling System Leak Testing (See: Engine,
Cooling and Exhaust/Cooling System/Testing and Inspection/Component Tests and General Diagnostics) and Cooling System Draining and
Filling (Static Fill) (See: Engine, Cooling and Exhaust/Cooling System/Service and Repair/Cooling System Draining and Filling (Static Fill)
).
2. Ignition OFF for 8 h or greater.
3. Ignition ON, observe the scan tool IAT Sensor and ECT Sensor parameters. The ECT, IAT, and ambient temperatures should be within 6掳C
(11掳F) of each other.
4. Use the scan tool to verify the proper operation of the engine cooling system fans.
Note: A critical analysis of the operation of the thermostat is necessary to properly diagnose these DTC.
5. Verify the proper heat range and the operation of the thermostat. Refer to Thermostat Diagnosis (See: Engine, Cooling and Exhaust/Cooling
System/Testing and Inspection/Symptom Related Diagnostic Procedures/Thermostat Diagnosis).
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.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the B34 ECT sensor.
2. Ignition OFF for 90 s, test for less than 5 ohm between the low reference circuit terminal A and ground.
瀚慖f greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20
ECM.
3. Ignition ON, verify the scan tool ECT Sensor parameter is less than -39掳C (-38掳F).
瀚慖f warmer than the specified range, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the K20
