Diagnostic Instructions
| • | Perform the Powertrain On Board Diagnostic (OBD) System Check prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provide an overview of each diagnostic category. |
DTC Descriptors
DTC 14: Engine Coolant Temperature (ECT) Sensor Circuit Low Temperature IndicatedDTC 15: Engine Coolant Temperature (ECT) Sensor Circuit High Temperature Indicated
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Varies with ambient temperature | |||
ECT Sensor Signal | 214°C (417°F) | -40°C (-40°F) | -40°C (-40°F)* |
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)* |
* Internal ECM or sensor damage may occur if the circuit is shorted to B+. | |||
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 signal circuit and supplies a ground to the low reference circuit.
The following table illustrates the difference between temperature, resistance, and voltage:
ECT | ECT Resistance | ECT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
Diagnostic Aids
| • | After starting the engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens. |
| • | Test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition. |
| • | If the vehicle has set overnight, the ECT sensor and the IAT sensor values should display within 3°C (5°F). |
Reference Information
Schematic Reference
Connector End View Reference
Engine Control Module Connector End Views
Electrical Information Reference
Scan Tool Reference
Engine Control Module Scan Tool Information
Circuit/System Verification
Engine idling, observe the DTC information with a scan tool. DTC 14 or 15 should not set.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the ECT sensor.
- Test for less than 5 ohms between the low reference circuit terminal A and ground.
- Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal B and ground.
- If all circuits test normal, test or replace the ECT sensor.
| ⇒ | 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 less than the specified range, test the signal circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
Component Testing
- Ignition OFF, disconnect the harness connector at the ECT sensor.
- Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.
Important: A thermometer can be used to test the sensor off the vehicle.
| ⇒ | If not within the specified range, replace the ECT sensor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Engine Control Module Replacement for ECM replacement, setup, and programming |
