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Home >> Geo >> 1997 >> Metro Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes 1.0 & 1.3L >> Diagnostic Trouble Code Tests >> DTC P0505 - Idle Control System >> Diagnosis & Repair

Diagnosis & Repair

  1. Connect scan tool to DLC. Start engine and allow to reach normal operating temperature. Clear DTC. Using scan tool, select RPM output control parameter. Observe ISC plunger while attempting to raise and lower idle speed with scan tool. If ISC plunger extends during increase in RPM and retracts during decrease in RPM, go to next step. If ISC plunger does not operate as specified, go to step 3).
  2. Turn ignition on. Review freeze frame data. Using scan tool, clear DTC information. Operate vehicle within freeze frame conditions. If DTC P0505 sets, go to next step. If DTC P0505 does not set, go to DIAGNOSTIC AIDS. Check for an intermittent problem. See the TESTS W/O CODES article.
  3. Turn ignition off. Disconnect ISC motor relay, located in engine compartment relay/fuse box. Turn ignition on. Using a test light connected to ground, probe ISC relay connector terminal No. 1 (White/Blue wire). If test light illuminates, go to next step. If test light does not illuminate, repair open in White/Blue wire between ISC relay and main relay. After repair is completed, go to step 11).
  4. Check continuity between ISC motor relay terminals No. 3 (Gray wire) and No. 4 (Gray/Yellow wire). If continuity does not exist, go to next step. If continuity exists, replace ISC motor relay. After repair is completed, go to step 11).
  5. Measure resistance between ISC motor relay terminals No. 1 (White/Blue wire) and No. 2 (Gray/Black wire). If resistance is 75-95 ohms, go to next step. If resistance is not as specified, replace ISC motor relay. After repair is completed, go to step 11).
  6. Turn ignition off. Disconnect PCM connectors. Using a fused jumper wire, connect ISC motor relay connector terminal No. 2 (Gray/Black wire) to battery voltage. Using a voltmeter, measure voltage at PCM 26-pin connector terminal No. 16 (Gray/Black wire). If battery voltage is exists, go to next step. If battery voltage does not exist, repair open or short in Gray/Black wire between ISC motor relay and PCM. After repair is completed, go to step 11).
    CAUTION: In next steps, DO NOT  apply 6 volts to ISC control circuit for longer than one second, or a fault condition may occur.
    NOTE: In next steps, using scan tool, ensure CTP switch is on and parameter indicates IDLE. If parameter does not indicate IDLE, move ISC actuator until CTP switch is on and parameter indicates IDLE.
  7. Turn ignition off. Disconnect PCM 26-pin connector. Backout PCM 26-pin connector terminals No. 11 (Gray/Yellow wire), No. 16 (Gray/Black wire), and No. 24 (Gray/Red wire). Reconnect PCM connector with specified wire terminals removed. Using a fused jumper wire, connect Gray/Black wire to ground. Turn ignition on. Ensure ISC motor actuator plunger contacts throttle lever. Connect 4, new 1.5 volt batteries in series. Connect Gray/Red wire to negative side of batteries. Momentarily connect Gray/Yellow wire to positive side of batteries. If ISC motor plunger extends out, go to next step. If ISC motor plunger does not extend out, go to step 10).
  8. Turn ignition on. Ensure ISC motor actuator plunger contacts throttle lever. Connect Gray/Yellow wire to negative side of batteries. Momentarily connect Gray/Red wire to positive side of batteries. If ISC motor plunger retracts, go to next step. If ISC motor plunger does not retract, go to step 10).
  9. Turn ignition off. Disconnect batteries and reinstall wire terminals into correct PCM 26-pin connector positions. Reconnect PCM connector. Turn ignition on. Disconnect ISC motor connector. Using a test light connected to battery voltage, probe ISC motor connector terminal No. 5 (Black/Blue wire). If test light illuminates, replace PCM. If test light does not illuminate, repair open in Black/Blue wire. After repair is completed, go to step 11).
  10. Check for an open or short in ISC motor control circuits (Gray/Yellow, Gray/Red and Gray wires) between ISC motor relay, ISC motor and PCM. Repair as necessary. If wires are okay, replace ISC motor. After repair is completed, go to next step.
  11. After repairs, using scan tool, clear DTC information. Road test vehicle within freeze frame conditions that set DTC. Check for DTCs. If no DTCs are stored, repair is complete. If any DTCs are set, go to appropriate DTC diagnostic test.
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