DTC p0128
Diagnostic Instructions
| • | 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. |
DTC Descriptor
Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
Diagnostic Fault Information
| 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 |
Typical Scan Tool Data
ECT Sensor Temperature
| 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) |
Circuit/system Description
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.
Conditions for Running the DTC
| • | 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 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. |
| • | 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. |
Conditions for Setting the DTC
| • | The ECM detects that the ECT is 10°C (18°F) colder than the first modeled ECT. |
| • | The ECM detects that the ECT is 11°C (20°F) colder than the second modeled ECT. |
Action Taken When the DTC Sets
DTC P0128 is a Type B DTC.
Conditions for Clearing the Mil/dtc
DTC P0128 is a Type B DTC.
Diagnostic Aids
| • | 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. |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference (Except Opel Gt)
| • | Testing for Intermittent Conditions and Poor Connections |
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information.
Circuit/system Verification
- Turn OFF the ignition.
- Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .
- If the ignition has been OFF for 8 hours or greater, the IAT sensor, the IAT sensor 2 and the ECT sensor should be within 9°C (16°F) of each other and also the ambient temperature. Ignition ON, observe the scan tool IAT Sensor, IAT Sensor 2, and the ECT Sensor parameters. Compare those sensor parameters to each other and also to the ambient temperature to determine if the ECT sensor is skewed colder.
- Engine running, observe the ECT Sensor parameter. The reading should be between -39 to +120°C (-38 to +248°F) depending on the current ambient temperature and the vehicle operating conditions.
- Use the scan tool to verify the proper operation of the engine cooling system fans.
- Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis .
- 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
- Ignition OFF, disconnect the harness connector at the ECT sensor.
- Inspect the ECT sensor terminals and the harness connector for corrosion.
- Ignition OFF for 90 seconds, test for less than 5 ohms between the low reference circuit terminal A and ground.
- Ignition ON, verify the scan tool ECT Sensor parameter is colder than -39°C (-38°F).
- Install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool ECT Sensor parameter is warmer than 142°C (288°F).
- If the circuits test normal, test or replace the ECT sensor.
Component Testing
Measure and record the resistance of the ECT sensor at various ambient temperatures, then compare those measurements to the Temperature Versus Resistance table.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Engine Coolant Temperature Sensor Replacement |
| • | Engine Coolant Thermostat Replacement |
| • | Control Module References for ECM replacement, setup, and programming |
