Engine Coolant Temperature Sensor - Diagnosis
Group: ENGINE ELECTRICALNumber: 98-36-006
Date: AUGUST, 1998
Model: ALL
Subject
ENGINE COOLANT TEMPERATURE SENSOR DIAGNOSIS
DESCRIPTION:
The engine coolant temperature sensor is located in the coolant passage of the cylinder head. It detects engine coolant temperature and sends signals to the powertrain control module (PCM). The engine coolant temperature sensor uses a thermistor which is sensitive to changes in temperature. The electric resistance of a thermistor decreases in response to a rise in temperature. Thus, when the temperature increases, the output voltage decreases The PCM determines engine coolant temperature by the sensor output voltage and provides optimum fuel enrichment when the engine is cold.
This bulletin provides diagnosis and repair procedures for engine coolant temperature sensors.
DIAGNOSTIC PROCEDURES:
DTC: Diagnostic Trouble Code
PCM: Powertrain Control Module
ECT: Engine Coolant Temperature
DIAGNOSTIC HINTS:
1. If the fast idle speed is not high enough or if the engine produces dark smoke during engine warm-up operation, a malfunctioning engine coolant temperature sensor might be the cause.
2. If the thermostat opening state is abnormal and causes overcooling, the Diagnostic Code (DTC) for the engine coolant temperature sensor can be set.
3. The Malfunction Indicator Lamp (MIL) is on or the DTC is set under the following conditions:
a. When the engine coolant temperature is detected by the sensor as below -40°C or above 120°C.
b. If the engine coolant temperature does not increase at least 5°C, even though 130 seconds or more have elapsed after starting the engine.
USING A VOLTMETER:
USING A SCAN TOOL:
HARNESS INSPECTION PROCEDURES:
SENSOR INSPECTION:
1. Remove the ECT sensor from the intake manifold.
2. With the temperature sensing portion of the ECT sensor immersed in hot water, check resistance.
3. If the resistance deviates from the standard value (as shown on the chart), replace the sensor.
INSTALLATION:
1. Apply sealant (LOCTITE962T or equivalent) to the threaded portion of the sensor.
2. Install ECT sensor and torque to 11-15 lb.ft.
3. Reconnect the harness connector securely.