Diagnostic Instructions
DTC Descriptor
DTC P2181 00: Engine Cooling System Performance
Circuit/System Description
The engine control module (ECM) controls the pulse width modulated (PWM) engine coolant thermostat heater. The thermostat controls coolant flow and regulates the engine operating temperature. Ignition voltage is supplied directly to the engine coolant
thermostat heater. The ECM controls the engine coolant thermostat heater by grounding the control circuit with a solid state device called a driver.
Conditions for Running the DTC
| • | DTCs P00B3 00, P00B4 00, P0101 00, P0102 00, P0103 00, P0112 00, P0113 00, or P0114 00 are not set. |
| • | The engine run time is between 70 s and 22 m. |
| • | The engine coolant temperature (ECT) sensor at start-up is between -20°C to +75°C (19 to 140°F). |
| • | The intake air temperature (IAT) sensor is between -7°C to +75°C (-4°F to +167°F). |
| • | The engine coolant thermostat heater command is greater than 50%. |
| • | The airflow into the engine is between 11 to 100 g/s. |
| • | The DTC runs once per ignition cycle when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects the engine coolant heated thermostat is stuck open for 160 s.
Action Taken When the DTC Sets
DTC P2181 00 is a Type B DTC
Conditions for Clearing the DTC
DTC P2181 00 is a Type B DTC
Diagnostic Aids
| • | Insufficient vehicle interior heating is an indication of improper thermostat operation. |
| • | The scan tool Desired ECT Sensor and the ECT Sensor parameters should be within 5°C (9°F) when the engine is at operating temperature. |
| • | A resistance condition in the ECT sensor circuits may cause this DTC. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. |
| • | The engine coolant thermostat heater has a mechanical fail-safe in case of an electrical condition with the thermostat heater. The mechanical thermostat will open at approximately 104°C (220°F). The mechanical thermostat will cycle from approximately
104°C (220°F) to approximately 98°C (208°F). |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, observe the DTC information with a scan tool. DTC P00B3 00, P00B4 00, P00B6 00, P0117 00, P0118 00, P0480 00, P0481 00, P0597 00, P0598 00, or P0599 00 should not
be set.
- Verify the coolant in the radiator surge tank is at the correct level and there are no engine coolant leaks. Refer to
Cooling System Draining and Filling and
Loss of Coolant.
- Engine idling for 15 m with the A/C OFF. Verify the engine cooing fan is not ON at all times. Refer to
Cooling Fan Always On.
Note: Depending on ambient temperature, it may take up to 4 m for the temperature to increase greater than the specified value.
- Command the Engine Coolant Thermostat Heater to 0% with a scan tool. Increase the engine speed to 3000 RPM. Observe the scan tool ECT sensor parameter. The temperature should increase to greater than 102°C (215°F).
| ⇒ | If less than the specified value, replace the E41 Engine Coolant Thermostat Heater. |
- 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.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
Engine Coolant Thermostat Replacement.
