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Diagnosis & Repair (Using OBD-II Scan Tool)

WARNING: This page is about a different car, the 2000 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
  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 behind passenger's side kick panel. Using an oscilloscope, backprobe between ground and terminal No. 26 (Green/Black wire) at ECM harness connector E4. 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 and measure voltage between ground and terminal No. 26 (Green/Black wire) at ECM harness connector E4. See Figure. If voltage is 9-14 volts, replace ECM. If voltage is not 9-14 volts, go to next step.
  4. Turn ignition off. Disconnect IAC valve harness connector. Measure voltage between ground and terminal No. 2 (Black/White 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 Green/Black wire between terminal No. 1 at IAC valve harness connector and terminal No. 26 at ECM harness connector E4. 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 - V6 & V8 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 MANUAL or AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. Repair as necessary.
Fig 1: Installing Jumper Wire Between DLC No. 1 Terminals
G99D52830Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 2: Identifying IAC Valve Waveform
G99H54152Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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