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Diagnosis & Repair

  1. Connect scan tool to DLC. Start engine and allow to reach normal operating temperature. Ensure vehicle is in closed loop operation. Monitor IAC duty cycle on scan tool. If duty cycle is 27-43 percent, go to next step. If duty cycle is not as specified, go to step 3).
  2. Select CLEAR INFORMATION function. Using scan tool, place vehicle into CHECK MODE. Operate vehicle within FREEZE FRAME conditions. If DTC P0505 resets, go to next step. If DTC P0505 does not reset, check for an intermittent problem. See TESTS W/O CODES article.
  3. Turn ignition on. Using a test light connected to ground, backprobe IAC valve connector cavity No. 2 (Black/Red wire). If test light comes on, go to next step. If test light does not come on, go to step 10).
  4. Using a voltmeter, backprobe between ground and PCM connector C3, terminal No. 10 (Black/Blue wire). If reading is 10-12 volts, go to step 6). If reading is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a voltmeter, measure voltage between ground and PCM connector C3, terminal No. 10 (Black/Blue wire). If reading is 10-12 volts, replace PCM. Retest system. If reading is not as specified, go to step 11).
  6. Using a voltmeter, backprobe between ground and PCM connector C3, terminal No. 9 (Black/White wire). If reading is 0.5 volt, go to step 8). If reading is not as specified, go to next step.
  7. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a voltmeter, measure voltage between ground and PCM connector C3, terminal No. 9 (Black/White wire). If reading is 12 volts, replace PCM. If reading is not as specified, go to step 12).
  8. Turn ignition off. Disconnect IAC valve harness connector. Remove IAC valve. Using a fused jumper wire, connect terminal No. 2 (Black/Red wire) of IAC valve to battery voltage. Connect terminal No. 3 (Black/White wire) to ground. If IAC valve closes, go to next step. If IAC valve does not close, replace IAC valve. Retest system.
  9. With jumper wire still connected to terminal No. 2, remove jumper wire from terminal No. 3 and connect to remaining terminal. If IAC valve opens, go to step 13). If IAC valve does not open, replace IAC valve. Retest system.
  10. Repair open or short in power feed circuit (Black/Red wire) between IAC valve and EFI F-HTR relay, located in engine compartment relay/fuse box. Retest system.
  11. Check for open or short in IAC valve open control circuit (Black/Blue wire) between IAC valve and PCM. Repair as necessary. If wire is okay, replace IAC valve. Retest system.
  12. Check for an open or short in IAC close control circuit (Black/White wire) between IAC valve and PCM. Repair as necessary. If wire is okay, replace IAC valve. Retest system.
  13. Turn ignition on. Using a voltmeter, measure voltage between ground and PCM connector C1, terminal No. 10 (Yellow/Blue wire). If reading is 10-12 volts, go to step 16). If reading is not as specified, go to next step.
  14. Turn ignition off. Disconnect PCM connector C1. Using a test light connected to battery voltage, probe PCM connector C1, terminal No. 10 (Yellow/Blue wire). If test light comes on, go to next step. If test light does not come on, replace PCM. Retest system.
  15. Check for a short in A/C ON signal circuit between A/C amplifier and PCM. (A/C ON signal wire is Red/White from A/C amplifier and turns to Yellow/Blue at PCM). Repair as necessary. If wire is okay, replace A/C amplifier. Retest system.
  16. Turn ignition on. Using a voltmeter, backprobe between ground and A/C amplifier connector terminal No. 3 (Red/Yellow wire). If reading is 10-12 volts, go to step 19). If reading is not as specified, go to next step.
  17. Backprobe between ground and PCM connector C1, terminal No. 21 (Red/Yellow wire). If reading is 10-12 volts, check for an intermittent problem. See TESTS W/O CODES article. If reading is not as specified, go to next step.
  18. Check for an open or short in A/C cut-out control circuit (Red/Yellow wire) between A/C amplifier and PCM. Repair as necessary. If wire is okay, replace PCM. Retest system.
  19. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on. Using a voltmeter, measure voltage between ground and PCM connector C1, terminal No. 21 (Red/Yellow wire). If reading is greater than 10 volts, replace IAC valve. If reading is not as specified, go to next step.
  20. Check for an open or short in A/C cut-out control circuit (Red/Yellow wire) between A/C amplifier and PCM. Repair as necessary. If wire is okay, replace A/C amplifier. Retest system.
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