Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSUBARU1998FORESTER L, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODESDIAGNOSTIC TESTSDTC P0117 (TW_HI): ECT SENSOR CIRCUIT HIGH INPUT (LEGACY)
1998 Subaru Forester L, Standard
DTC P0117 (TW_Hi): ECT Sensor Circuit High Input (Legacy)
1998 Subaru Forester L, StandardSECTION DTC P0117 (TW_Hi): ECT Sensor Circuit High Input (Legacy)
- Turn ignition off. Connect scan tool. Start engine. Observe coolant temperature display. If displayed value is more than -40°F (-40°C), repair poor contact in connectors or wiring of ECT sensor connector or PCM connector. If displayed value is less than -40°F (-40°C), go to next step.
- Turn ignition off. Remove idle air control solenoid valve by-pass air hose. Disconnect ECT sensor connector. Using a voltmeter connected to ground, measure voltage at ECT sensor connector terminal No. 1 (Black/Yellow wire). If voltage reading is more than 10 volts, repair short circuit in wiring between ECT sensor connector and PCM connector. If voltage reading is 10 volts or less, leave voltmeter connected and go to next step.
- Turn ignition on. If voltage reading is more than 10 volts, repair short circuit in wiring between ECT sensor connector and PCM connector. If voltage reading is 4 volts or less, repair poor contact in connectors or wiring of ECT sensor connector or PCM connector. If voltage reading is 4-10 volts, go to next step.
- Turn ignition off. Using an ohmmeter, measure resistance of wiring between ground and ECT sensor connector terminal No. 2 (Black wire). If resistance is 5 ohms or less, replace ECT sensor. If resistance is more than 5 ohms, check for an open in harness between PCM and ECT sensor or for poor connection at PCM or ECT sensor connectors.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.