• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance |
---|---|---|---|---|---|
ECT Sensor Signal | P0117 | P0118 | P0118 | P0118 | P0116, P0119, P0128 |
Low Reference | -- | P0118 | P0118 | P0118 | P0119, P0128 |
Circuit | Short to Ground | Open | Short to Voltage |
---|---|---|---|
Operating Conditions: Engine Running Parameter Normal Range: -39 to +120°C (-38 to +248°F) | |||
ECT Sensor Signal | 143°C (289°F) | -40°C (-40°F) | -40°C (-40°F) |
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F) |
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT sensor signal circuit and a ground for the low reference circuit.
The purpose of this diagnostic is to analyze the performance of the ECT sensor and the thermostat by comparing the measured ECT to the following 2 distinct models:
• | The first model will analyze the performance of the ECT sensor, by using the ECT sensor to determine if the temperature of the engine coolant increases at the correct rate, by comparing it to a modeled ECT under various operating conditions. |
• | The second model will analyze the performance of the thermostat, by using the ECT sensor to determine if the temperature of the engine coolant increases at the correct rate, and then maintains that temperature within a calibrated range of the modeled ECT under various operating conditions. |
The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and then maintains that temperature within a calibrated range of the modeled ECT.
• | DTCs P0100, P0101, P0102, P0103, P0112, P0113, P0114, P0116, P0117, P0118, P0119, or P0502 is not set. |
• | The start-up ECT is colder than 39°C (102°F). |
• | The engine run time is between 30-500 seconds. |
• | The vehicle has traveled greater than 0.8 kilometer (0.5 mile) at greater than 8 km/h (5 mph). |
• | The mass air flow (MAF) average is greater than 1 g/s |
• | This model of the DTC runs once per ignition cycle within the enabling conditions. |
AND |
• | DTCs P0100, P0101, P0102, P0103, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0502, or P0503 is not set. |
• | The start-up ECT is colder than 70°C (158°F). |
• | The estimated ambient air temperature is between -11 and +70°C (+12 and +158°F). |
• | The model calculated ECT is colder than 89°C (192°F) |
• | The engine speed is greater than 960 RPM. |
• | The vehicle has traveled greater than 0.8 kilometer (0.5 mile) at greater than 15 km/h (9 mph). |
• | The accumulated MAF is greater than 3,000 g. |
• | This model of the DTC runs continuously within the enabling conditions. |
• | The ECM detects that the ECT is 10°C (18°F) colder than the first modeled ECT. |
AND/OR |
• | The ECM detects that the ECT is 11°C (20°F) colder than the second modeled ECT. |
DTC P0128 is a Type B DTC.
DTC P0128 is a Type B DTC.
• | DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation. |
• | Corrosion on the ECT sensor terminals or the ECT harness connector results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. |
• | 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. |
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information.
Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.
⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
⇒ | If warmer than the specified range, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If colder than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
Measure and record the resistance of the ECT sensor at various ambient temperatures, then compare those measurements to the Temperature Versus Resistance table.
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for ECM replacement, setup, and programming |