Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
- Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Turn on scan tool. Start engine and allow it to idle. Monitor MAF rate. If scan tool reading is 0.0 gm/sec., go to next step. If reading is 160.0 gm/sec. or more once engine is at normal operating temperature, go to step 5.
- Disconnect MAF sensor 5-pin connector. Turn ignition on. Using voltmeter, measure voltage between terminals No. 1 (Black/White) and No. 5 (Brown wire) at MAF sensor wiring harness connector. See Fig 1. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, see 7.
- Access ECM behind glove box. Start engine. Ensure A/C is off. Backprobing ECM connector, measure voltage between ECM connector E9 terminal No. 24 (Red wire) and ECM connector E10 terminal No. 28 (Brown wire). If voltage is .5-3.0 volts, replace ECM and retest system. If voltage is not .5-3.0 volts, go to next step.
- Check for short or open circuits in wiring between ECM and MAF sensor. See WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, replace MAF sensor.
- Access ECM behind glove box. Turn ignition off. Backprobing, check for open circuit between ECM connector E9 terminal No. 32 (Blue/White wire) and ECM connector E10 terminal No. 28 (Brown wire). If resistance is one ohm or less, go to next step. If resistance is not one ohm or less, replace ECM.
- Check for open or short circuit in wiring between ECM and MAF sensor. See WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, replace MAF sensor.
- Disconnect negative battery cable. Disconnect ECM E6 and E9 connectors. Check for open circuit between ECM E6 connector terminal No. 1 (Black/Red wire) and terminal No. 3 of computer relay at relay block. Resistance should be one ohm or less. Disconnect ECM E9 connector. Check for open circuit in Blue/White wire between terminal No. 32 (Blue/White wire) and MAF sensor. Resistance should be one ohm or less. If resistances are to specification, check ECM power source circuit. If resistances are not to specification, check and replace harness and connector. See WIRING DIAGRAMS article.