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 P0123 (THV_HI): TP SENSOR CIRCUIT LOW INPUT
1998 Subaru Forester L, Standard
DTC P0123 (THV_Hi): TP Sensor Circuit Low Input
1998 Subaru Forester L, StandardSECTION DTC P0123 (THV_Hi): TP Sensor Circuit Low Input
- Turn ignition off. Connect scan tool. Start engine. Observe TP sensor output signal. If displayed voltage is more than 4.9 volts, go to next step. If displayed voltage is 4.9 volts or less, system is normal. Check for poor contact in connectors of TP sensor and PCM.
- Turn ignition off. Disconnect TP sensor connector. Check resistance of harness between ground and TP sensor connector terminal No. 1 (Black wire). If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, check for an open between TP sensor and PCM connectors.
- Turn ignition on. Using voltmeter, measure voltage between ground and TP sensor connector terminal No. 2 (White wire). If voltage is 4.9 volts or less, replace TP sensor. If voltage is more than 4.9 volts, check for short in wiring between TP sensor and PCM connector. Repair as necessary. After repairing short, check PCM operation and replace if necessary. Retest system.
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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.