1-2-3 (Engine Temperature Sensor Signal Absent Or Faulty)
- Connect measuring unit to fuel injection ECU. See MEASURING UNIT under SELF-DIAGNOSTIC SYSTEM. Turn ignition on. Connect voltmeter between measuring unit terminals No. 14 and 15. Voltmeter should indicate about 1.8 volts at 68°F (20°C) and about 250 millivolts when engine is at operating temperature.
- If voltage is not to specification, check output voltage from fuel injection ECU. Disconnect temperature sensor connector. Turn ignition on. Connect voltmeter between measuring unit terminals No. 14 and 15. About 5 volts should be present.
- If voltage is not to specification, check circuit between temperature sensor and ECU for an open or short circuit. If circuit is okay, repeat test using new ECU. If circuit is not okay, go to next step.
- Ensure ignition is off. Repair circuit between temperature sensor and ECU, ensuring sensor terminal No. 14 is grounded. Connect ohmmeter between measuring unit terminals No. 20 and 14. Ohmmeter should indicate about zero ohms. If resistance is not to specification, repeat test using new fuel injection ECU.
- If resistance is to specification, check resistance between measuring unit terminals No. 14 and 15. Refer to the TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table. If resistances are not to specification, replace sensor or repair wiring as necessary. Clear any codes in other systems.
TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS
| Temperature °F (°C) | Ohms |
|---|---|
| 68 (20) | 2800 |
| 140 (60) | 560 |
| 194 (90) | 206 |