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Home >> Toyota >> 2000 >> Corolla VE, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P0505: Idle Air Control (IAC) System Circuit >> Diagnosis & Repair (Using OBD-II Scan Tool)
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Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Start engine and warm to normal operating temperature. Turn all accessories off. Ensure A/C is off. Shift transaxle lever into Neutral. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Note engine RPM. Using a jumper wire, connect terminals TE1 and E1 at DLC No. 1 in engine compartment. See Fig 1. Note engine RPM and compare RPM readings. If difference in engine speed is more than 100 RPM, go to step  9. If difference in engine speed is 100 RPM or less, go to next step.
  2. Turn ignition off. Access ECM below stereo, behind instrument panel, just in front of center console. On models with 4A/T transmission, connect an oscilloscope by backprobing between ground and terminal No. 18 (Blue/Black wire) at ECM harness connector E7. See Figure. On models without 4A/T transmission, connect an oscilloscope by backprobing between ground and terminal No. 15 (Blue/Black wire) at ECM harness connector E4. See Figure. On all models, start engine and let idle. Oscilloscope waveform should be as illustrated. See Fig 2. If waveform is as shown, go to step  6. If waveform is not as shown, go to next step.
  3. Turn ignition off. Turn ignition on. Using DVOM, backprobe ECM harness connector. On models with 4A/T transmission, measure voltage between ground and terminal No. 18 (Blue/Black wire) at ECM harness connector E7. On models without 4A/T transmission, measure voltage between ground and terminal No. 15 (Blue/Black wire) at ECM harness connector E4. On all models, voltage should be 9-14 volts. If voltage is as specified, replace ECM. If voltage is not as specified, go to next step.
  4. Turn ignition off. Disconnect IAC valve harness connector. Measure voltage between ground and terminal No. 2 (Black wire) at IAC valve harness connector. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, repair IAC valve power distribution circuit. See WIRING DIAGRAMS article.
  5. Check for open or short in Blue/Black wire between IAC valve and ECM. See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace IAC valve.
  6. Check IAC valve operation. See IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If problem exists, go to next step. If problem does not exist, go to step  8.
  7. Check for open in Brown wire between ground and terminal No. 3 at IAC valve harness connector. See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace IAC valve.
  8. Remove IAC valve from throttle body. Check IAC valve and passages for carbon build-up and blockage. If problem exists, repair or replace as necessary. If problem does not exist, go to next step.
  9. Ensure oil dipstick, oil filler cap, PCV system and all other air induction system components are intact and operating properly. If problem exists, repair as necessary. If problem does not exist, an open or short in A/C switch signal circuit may exist. Check A/C amplifier. See appropriate article in AIR CONDITIONING & HEATING. Repair as necessary.
Fig 1: Installing Jumper Wire Between DLC No. 1 Terminals
G98E11225Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 2: Identifying IAC Valve Waveform
G99H54152Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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