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 MANUALSSUBARU1994LEGACY L, 4D SEDAN, FWD, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODESDIAGNOSTIC CODE TESTINGCODE 31 - THROTTLE POSITION SENSOR
1994 Subaru Legacy L, 4D Sedan, FWD, Standard
Code 31 - Throttle Position Sensor
1994 Subaru Legacy L, 4D Sedan, FWD, StandardSECTION Code 31 - Throttle Position Sensor
NOTE:
Refer to illustration for ECU connector and terminal identification. See Figure
.
- Turn ignition on. Measure voltage between ECU connector B58, terminal No. 2 (backprobe) and ground with throttle fully open and fully closed. With throttle open, .7-1.6 volts should be present. With throttle closed, 4.4-4.8 volts should be present. Voltage should smoothly increase/decrease as throttle is opened/closed. Backprobe ECU connector B58, terminals No. 1 and 3 with voltmeter to ground. Terminal No. 1 should be zero volts. Terminal No. 3 should be 5 volts.
- If voltages are to specification, check ECU terminals for poor contact. If terminals are okay, replace ECU. If voltages are not to specification, go to next step.
- Turn ignition off. Disconnect throttle position sensor connector. Measure resistance between throttle position sensor terminals No. 2 (Black wire) and No. 3 (Red wire). Ohmmeter should indicate 12,000 ohms.
- Measure resistance between throttle position sensor terminals No. 2 (Black wire) and No. 4 (White wire). With throttle fully closed, 10,000-12,000 ohms should be present. With throttle fully open, 3000-5000 ohms should be present. If resistances are not to specification, replace throttle position sensor. If resistances are to specification, go to next step.
- Disconnect ECU and throttle position sensor connectors. Measure resistance between ECU connector B58, terminal No. 1 and throttle position sensor connector terminal No. 2 (Black wire). Measure resistance between ECU connector B58, terminal No. 2 and throttle position sensor connector terminal No. 4 (White wire). Measure resistance between ECU connector B58, terminal No. 3 and throttle position sensor connector terminal No. 3 (Red wire). Zero ohms should be present in all cases. If resistance readings are not zero ohms, repair harness as necessary.
- Measure resistance between throttle position sensor connector terminals No. 2 (Black wire), No. 4 (White wire), No. 3 (Red wire), and ground. Minimum of one megohm resistance should be present in all cases. If minimum of one megohm resistance is not present, replace throttle position sensor.
- If resistances are to specification, repair poor terminal contact at ECU. If terminal contact is okay, replace ECU.
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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.