1993 Subaru Justy BaseFACTORY OEM SERVICE PROCEDURE

Code 42: Idle Switch

NOTE: Refer to illustration for ECU connector and terminal identification. See Figure .
  1. Turn ignition on. Backprobing ECU connector F120, measure voltage between ground and terminal No. 16 (Green/Red wire) of ECU. With throttle closed, voltage should be less than one volt. With throttle fully open, voltage should be more than 8 volts. If voltage is not as specified, go to next step. If voltage is as specified, check for poor ECU connector contact. Repair connector and/or wiring harness as necessary. If connector and wiring harness are okay, replace ECU.
  2. Turn ignition off. Disconnect throttle switch connector. Measure resistance between terminal No. 2 and terminal No. 3 at throttle switch. See Fig 1 . With throttle closed, resistance should be less than one ohm. With throttle fully open, resistance should be infinite. If resistance is as specified, go to next step. If resistance is not as specified, check throttle switch adjustment. See ADJUSTMENTS article. If throttle switch is adjusted properly, replace throttle switch.
    Fig 1: Identifying Throttle Switch Terminals (Justy)
    G93G80685Courtesy of SUBARU OF AMERICA, INC.
  3. Disconnect ECU connectors. Measure resistance between ECU and throttle switch connectors and between ECU connector and ground. See IDLE SWITCH RESISTANCE SPECIFICATIONS  table. If resistance is as specified, check for poor ECU connector contact. Repair connector and/or wiring harness as necessary. If connector and wiring harness are okay, replace ECU. If resistance is not as specified, repair connector and/or wiring harness as necessary.
IDLE SWITCH RESISTANCE SPECIFICATIONS

Measure Between Terminals Ohms
No. 1 (1) & No. 2 (2) Less Than One
No. 1 (1) & Ground Less Than 10
No. 6 (3) & Ground Infinite
No. 6 (3) & No. 3 (2) Less Than One
No. 10 (3) & Ground Less Than 10
No. 10 (3) & No. 2 (2) Less Than 10
(1) Measure at ECU connector F119.
(2) Measure resistance at throttle switch connector. See Fig 1 .
(3) Measure at ECU connector F120.
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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.