LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Subaru >> 1994 >> Legacy Alpine >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Code Testing >> Code 42 - Idle Switch
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Code 42 - Idle Switch

NOTE: Refer to illustration for ECU connector and terminal identification. See Figure .
  1. Turn ignition on. Measure voltage between ECU connector B56, terminal No. 6 (backprobe) and ground. Zero volts should be present with throttle fully closed. About 5 volts should be present with throttle open. If voltages are not to specification, go to next step. If voltages are to specification, check ECU terminals for poor contact or replace ECU.
  2. Disconnect throttle sensor connector. Measure resistance between throttle sensor idle switch Brown wire and Black wire terminals. With throttle closed, zero ohms should be present. With throttle open, minimum of one megohm should be present. If resistances are not to specification, adjust switch as necessary. See information in ADJUSTMENTS article. If resistances are to specification, go to next step.
  3. Disconnect ECU and throttle sensor connectors. Measure resistance between ECU connector B56, terminal No. 6 and throttle sensor connector terminal No. 1 (Brown wire), then measure resistance between ECU connector B58, terminal No. 1 and throttle sensor connector terminal No. 2 (Black wire). If zero ohms are present in both cases, go to next step. If zero ohms are not present in both cases, repair harness or connector.
  4. Check resistance between ground and idle switch terminals No. 1 and 2. At least one megohm resistance should be present. If at least one megohm resistance is not present, replace idle switch. If at least one megohm is present and zero ohms were present in previous step, check ECU terminals for poor contact or replace ECU
scientia non olet · About LEMON Manuals