Diagnosis & Repair Procedure
NOTE:
For better performance and results of this diagnostic procedure, usage of appropriate wiring diagram is recommended. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS
article in ELECTRICAL.
NOTE:
Perform all voltage and resistance tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use an ohmmeter to isolate wiring harness shorts or opens.
- If engine system check has been performed, go to next step. If engine system check has not been performed, perform A-4: ENGINE SYSTEM CHECK under SYSTEM TESTS, then go to next step.
- Start engine and allow it to reach normal operating temperature. Using scan tool, read MAF sensor values at idle speed and at 2500 RPM. MAF sensor value should be 1.5-4.0 grams/second at idle speed, and 5-10 grams/second at 2500 RPM. If MAF sensor values are not as specified, go to next step. If MAF sensor values are as specified, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. After repair, repeat DTC CONFIRMATION TEST .
- Turn ignition switch to LOCK position. Disconnect MAF sensor 3-pin harness connector C32, located between air cleaner box and intake hose. See Figure . Turn ignition switch to ON position. Measure voltage between ground and MAF sensor harness connector C32 terminal No. 3 (Blue/Black wire). See Fig 1 . If voltage is 10-14 volts, go to next step. If voltage is less than 10 volts, repair open circuit in Blue/Black wire between ECM and MAF sensor. After repair, repeat DTC CONFIRMATION TEST .
- Turn ignition switch to LOCK position. Remove ECM, see ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article. Check ECM and harness connector terminals for corrosion or poor connection. If connector terminals are faulty, repair as necessary and repeat DTC CONFIRMATION TEST . If connector terminals are okay, reconnect ECM harness connectors. Turn ignition to ON position. Backprobe and measure voltage between ECM harness connector C51-3 terminals No. 5 (Purple/Green wire) and No. 10 (Purple/White wire). See Figure . If voltage is 1.0-1.6 volts, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST . If voltage is not 1.0-1.6 volts, check MAP sensor and harness connector for proper connection. Also check Purple/White wire for open circuit between ECM and MAP sensor. If MAP sensor connection and circuit are faulty, repairs necessary and repeatDTC CONFIRMATION TEST . If MAP sensor connection and circuit are okay, replace MAF sensor. See MASS AIR FLOW SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION article. After repair, repeatDTC CONFIRMATION TEST .