| Table 1: | Resistance of ECT Sensor Unit |
Circuit Description
The engine control module (ECM) applies a voltage, about 5 volts, through a pull-up resistor to the engine coolant temperature (ECT) signal circuit.
When the engine coolant is cold, the sensor or thermistor resistance is high, and the ECM will measure a high signal voltage. As the engine coolant warms, the sensor resistance lowers, and the ECT signal voltage measured at the ECM drops. With a fully warmed engine, the ECT signal voltage should measure about 1.5-2 volts. If the ECM detect a continuous open in the ECT sensor or circuit, then DTC 0023 will set.
Conditions for Setting the DTC
ECT sensor voltage exceeding 4.8 volts or lower than 0.1 volts continues for 1 second.
| • | 4.8 volts = -50°C (122°F) |
| • | 0.1 volts = 110°C (230°F) |
Action Taken When the DTC Sets
| • | Starting: Based on -20°C (-4°F) |
| • | Other: Based on 80°C (176°F) |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
DTC 0023 can be cleared by using the Clear Info on the scan tool or by using the Diag Clear Switch.
Diagnostic Aids
Inspect for the following conditions:
| • | Poor connection at the ECM |
| Inspect the harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection. |
| • | Damaged harness |
| Inspect the wiring harness for damage, shorts to ground, shorts to battery, and open circuits. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the ECT sensor. A change in the ECT scan tool display will indicate the location of the fault. |
| • | Smoke observed when started after warming up |
| • | Excessive white smoke when started in cold weather |
Coolant Temperature | Resistance (kohms) |
|---|---|
20°C (68°F) | About 2.7 (2.5 V) |
40°C (104°F) | 1.3 (1.6 V) |
60°C (140°F) | 0.6 (0.9 V) |
80°C (176°F) | 0.4 (0.65 V) |
Step | Action | Value | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
1 | Does DTC 0023 set with the ignition ON or the engine running? | -- | Go to Step 2 | Go to Diagnostic Aids | ||||
2 |
Important: When voltage is abnormally high, e.g. 12 V, may be short circuit with B+ line. Measure the voltage between pin number 30 of ECM connector C1 and pin number 66 at the ECM connector C2 while the ignition is ON and engine is running. Does the voltage measure within the specified range of 0.65 V when coolant temperature is about 80°C (176°F)? | 0.1-4.8 V | Go to Step 4 | Go to Step 3 | ||||
3 | Inspect for poor connections between the connector and ECT sensor, or a temporarily overheated engine. Did you find a condition? | -- | Go to Step 4 | Go to Step 5 | ||||
4 | Repair the engine cooling system fault such as the radiator, fan, and thermostat. Did you complete the repair? | -- | Go to Step 2 | -- | ||||
5 |
Does the resistance measure less than the specified value? | 2 ohms | Go to Step 6 | Go to Step 9 | ||||
6 | Measure the resistance between pin number 30 of ECM connector C1 and GND on the ECT sensor harness. Does the resistance measure more than the specified value? | 10 M ohms | Go to Step 7 | Go to Step 9 | ||||
7 |
Is resistance near the value on the table? | -- | Go to Step 8 | Go to Step 10 | ||||
8 |
Does DTC 0023 reset? | -- | Go to Step 11 | System OK | ||||
9 | Repair/replace the ECT sensor wiring harness. Did you complete the action? | -- | Go to Step 12 | -- | ||||
10 | Replace the ECT sensor. Did you complete the replacement? | -- | Go to Step 12 | -- | ||||
11 | Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||
12 | Clear all DTCs. Does DTC 0023 reset? | Go to Step 2 | System OK | |||||
