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Home >> Ford >> 1988 >> Bronco II 4WD, Standard, M5OD-R1 >> Repair and Diagnosis >> Engine Performance >> System >> EEC-IV CEC System >> Quick Test >> Test B3 - Mass Airflow Sensor (MAF)
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Test B3 - Mass Airflow Sensor (MAF)

NOTE: Perform this test when Service Code 26, 56, or 66 in generated in the QUICK TESTS or when directed here by test charts.
Fig 1: Mass Airflow Sensor (MAF) Circuits
G54774

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: air cleaner element, inlet air duct, or throttle body.

  1. Voltage Check at MAF Sensor  - Turn key off and disconnect MAF sensor from vehicle harness. Set DVOM on 20-volt scale. Measure voltage between MAF Signal pin connector and battery negative terminal. If voltage is greater than 1.5 volts, service short. Reconnect MAF sensor and rerun QUICK TEST  . If voltage is less than 1.5 volts, replace MAF sensor and rerun QUICK TEST.
  2. Checking Continuity of Power Ground Circuit  - Set DVOM on 200-ohm scale. With key off and MAF sensor disconnected, measure resistance between PWR ground circuit pin at MAF sensor connector and battery negative (-) terminal. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair circuit. Reconnect MAF, and rerun QUICK TEST  .
  3. Checking MAF Signal Return Circuit  - With key off and MAF sensor disconnected, set DVOM on 200-ohm scale. Disconnect ECA 60 pin connector, inspect connector and terminals. Install breakout box. Measure resistance between MAF signal return, at MAF sensor, and Test Pin No. 9. If resistance is less than 5 ohms go to next step. If resistance is more than 5 ohms, repair circuit and rerun QUICK TEST  .
  4. Engine Running: Code 26  - Check voltage to VPWR. Set DVOM to 20-volt scale. With key off, disconnect MAF sensor connector. With KOEO, measure voltage between VPWR at MAF sensor and battery negative (-) terminal. If voltage is greater than 10.5 volts go to next step. If voltage is less than 10.5 volts, go to TEST A2  , step 1).
  5. Checking MAF Sensor Ground  - Set DVOM on 20-volt scale. With KOEO and MAF sensor disconnected, measure voltage between VPWR circuit and PWR ground circuit at MAF sensor connector. If voltage is greater than 10.5 volts, go to next step. If voltage is lower than 10.5 volts, service open in PWR ground circuit and rerun QUICK TEST  .
  6. Checking MAF SIG and VPWR Circuit Continuity  - With key off and MAF sensor disconnected, set DVOM on 20-volt scale. Disconnect ECA 60-pin connector, inspect pins and install breakout box. Measure resistance between MAF signal, at sensor connector, and Test Pin No. 50 at breakout box. Measure resistance between VPWR, at the MAF sensor connector, and Test Pins No. 37 and 57 at breakout box. If resistance is less than 5 ohms but vehicle does not start, or starts and stalls, go to step 2) of this test. If vehicle starts, go to next step. If resistance is more than 5 ohms, remove breakout box. Service open circuit an rerun QUICK TEST  .
  7. Checking MAF SIG For Shorts  - With key off and breakout box installed, disconnect MAF sensor and ECA. Set DVOM on 200K-ohm scale. Measure resistance between Test Pin No. 50 and Pins No 40, 9, and 60 at breakout box. If resistances are greater than 10K ohms, go to Step 2) of this test. If resistances are less than 10K ohms, remove breakout box and service open circuit.
  8. MAF Sensor Resistance  - With key off, breakout box installed, and ECA disconnected, reconnect MAF sensor. Set DVOM on 20K-ohm scale. Measure resistance between Test Pin No. 50 and Test Pins No. 9, 40, and 60 at the breakout box. If all resistances are less than 10K ohms, remove breakout box. Replace ECA and rerun QUICK TEST  . If resistances are greater than 10K ohms, remove breakout box and replace MAF sensor. Reconnect ECA and run QUICK TEST.
  9. KOEO Self Test With MAF Disconnected  - With key off and MAF sensor disconnected, rerun KEY ON/ENGINE OFF (KOEO) SELF-TEST  . If code 66 is displayed, replace MAF sensor and rerun QUICK TEST  . If no code 66 is displayed, go to next step.
  10. Checking MAF Signal for Short to Power  - With key off, install breakout box and disconnect MAF sensor and ECA. Set DVOM on 200K-ohm scale. Measure resistance between MAF signal and VPWR at MAF sensor connector. If resistance is greater than 10K ohms, remove breakout box. Reconnect MAF sensor, replace ECA, and rerun QUICK TEST  . If resistance is less than 10K ohms, repair circuit short and rerun QUICK TEST.
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