TESTING

1985–86 Sedan, Coupe and Wagon

WITH SPFI

1. Switch the ignition OFF.
2. Disconnect the electrical harness from the MAF sensor and remove the rubber cover from the MAF sensor connector.

   WARNING
   Be careful not to short-circuit the power source. Do not apply voltage greater than 12V.

3. Connect a voltage of 12V to the MAF sensor's positive terminal B and negative terminal C.
4. Using a voltmeter, measure the voltage between terminal C and terminal D of the MAF sensor; it should be 0.1–0.5V.
5. Blow air through the MAF sensor's by-pass passage. If the reading does not change, replace the MAF sensor.

1987–89 Sedan, Coupe and Wagon

WITH SPFI

1. Switch the ignition OFF.
2. Disconnect the electrical wiring from the MAF sensor and remove the rubber cover from the MAF sensor connector.
3. Using an ohmmeter, make the following measurements at the MAF sensor connector:
   • Terminal B and ground — less than 10 ohms.

   NOTE: If resistance is greater than 10 ohms, check the harness and internal circuits of the control unit for discontinuity.

4. Switch the ignition ON.
5. Using a voltmeter, measure the voltage between terminal R of the MAF sensor harness and ground; it should be 10V or more.

   NOTE: If the voltage is not within specifications, check the condition of the battery, fuse, control unit harness and/or connector in the power line.

6. Connect the electrical wiring to the MAF sensor.
7. Using a voltmeter, measure the voltage between terminal W and terminal B of the MAF sensor connector; it should be 0.1–0.5V.

   NOTE: If the voltage is not within specifications, replace the mass airflow sensor.

8. Remove the upper section the air cleaner.
9. Blow air through the MAF sensor, from the air cleaner side, while measuring the voltage between terminal W and terminal B of the MAF sensor connector. If the reading is not 0.1–0.5V, replace the mass airflow sensor.

1988–89 STD, DL and GL

WITH MPFI

1. Switch the ignition OFF.
2. Disconnect the electrical wiring from the MAF sensor and remove the rubber cover from the MAF sensor connector.
3. Using an ohmmeter, make the following measurements at the MAF sensor connector:
   • Terminal B and ground — less than 10 ohms.
   • Terminal BR and ground — less than 10 ohms.

   NOTE: If resistance is greater than 10 ohms, check the harness and internal circuits of the control unit for discontinuity and/or the ground terminal on the intake manifold for poor contact.

4. Switch the ignition ON and connect the electrical wiring to the MAF sensor.
5. Using a voltmeter, measure the voltage between the SA terminal of the MAF sensor connector and ground; it should be 10V or more.

   NOTE: If the voltage is not within specifications, check the condition of the battery, fuse, control unit harness and/or connector in the power line.

6. Using a voltmeter, measure the voltage between the SA terminal and the BR terminal of the MAF sensor connector; it should be 1–2V.

   NOTE: If the voltage is not within specifications, replace the mass airflow sensor.

7. Disconnect MAF sensor from air cleaner.
8. Blow air through the MAF sensor, from the air cleaner side, while measuring the voltage between the SA terminal and the BR terminal of the MAF sensor connector. If the reading is not 1–2V, replace the mass airflow sensor.
9. Install the MAF sensor onto the air cleaner.
10. Start and warm the engine.
11. Drive the vehicle at 15 mph for at least 1 minute.
12. Rev the engine above 2000 rpm and allow it to idle.
13. Using a voltmeter, measure the voltage between the light red wire terminal of the MAF sensor and ground; it should be 0V.
14. Turn the ignition switch OFF.
15. Using a voltmeter, measure the voltage, within 1 second after turning the engine OFF, between the light red wire terminal of the MAF sensor and ground; it should be 12V.

    NOTE: If the voltage is not within specifications, check the harness from the control unit to the MAF sensor for discontinuity.

1985–86 Sedan, Coupe, Wagon and XT With MPFI

1. Switch the ignition to ON.
2. Using a voltmeter, measure the voltage between the LY terminal of the MAF and ground.
   1. If the voltage is approximately 5.0V, go to Step 3.
   2. If the voltage is not approximately 5.0V, go to Step 6.
3. Using a voltmeter, make sure the MAF sensor flap is fully closed and measure the voltage between the YR terminal of the MAF and ground.
   1. If the voltage is approximately 1.0V, go to Step 4.
   2. If the voltage is not approximately 1.0V, go to Step 5.
4. Using a voltmeter, make sure the MAF sensor flap is fully opened and measure the voltage between the YR terminal of the MAF and ground.
   1. If the voltage is approximately 5.0V, replace the control unit.
   2. If the voltage is not approximately 5.0V, replace the MAF sensor.
5. Turn the ignition switch OFF and disconnect the electrical wiring from the MAF sensor. Using a ohmmeter, make sure the MAF sensor flap is fully closed and measure the resistance between the YR terminal of the MAF sensor and ground.
   1. If the resistance is approximately 50 ohms, repair YR (US) wire between the MAF sensor and the control unit.
   2. If the resistance is not approximately 50 ohms, replace the MAF sensor.
6. Using a voltmeter, measure the voltage between the G terminal of the MAF and ground.
   1. If the voltage is approximately 8.0V, go to Step 8.
   2. If the voltage is not approximately 8.0V, go to Step 7.
7. Turn the ignition switch OFF. Disconnect the electrical wiring from the control unit. Using a ohmmeter, measure the resistance between the G terminal of the MAF sensor and ground.
   1. If the resistance is 0 ohms, repair G (UB) wire between the MAF sensor and the control unit and/or replace the control unit.
   2. If the resistance is not 0 ohms, replace the control unit.
8. Turn the ignition switch OFF. Disconnect the electrical wiring from the MAF sensor. Using an ohmmeter, make the following measurements at the MAF sensor connector:
   • Resistance between terminal G and ground — approximately 300 ohms
   • Resistance between terminal LY and ground — approximately 200 ohms
   • Resistance between terminal YR and ground (from flaps closing to opening) — approximately 50–300 ohms
   1. If all of the above resistance's are met, go to Step 9.
   2. If all of the above resistance's are not met, replace the MAF sensor.
9. Using an ohmmeter, measure the resistance between terminal YL of the MAF sensor connector and ground.
   1. If the resistance is 0 ohms, go to Step 10.
   2. If the resistance is not 0 ohms, repair the ground wire.
10. Disconnect the electrical wiring from the control unit. Using an ohmmeter, measure the resistance between terminal LY of the MAF sensor connector and ground.
    1. If the resistance is 0 ohms, repair the shorted wiring harness.
    2. If the resistance is not 0 ohms, go to Step 11.
11. Using an ohmmeter, measure the resistance between terminal LR of the MAF sensor connector and ground.
    1. If the resistance is 0 ohms, repair the shorted wiring harness.
    2. If the resistance is not 0 ohms, repair the wiring harness between the MAF sensor and the control unit.
12. Reconnect the electrical harness connectors between the control unit and the MAF sensor.

1987 Sedan, Coupe and Wagon With MPFI, 1987–89 XT and 1988–89 XT6

1. Switch the ignition OFF.
2. Disconnect the electrical wiring from the MAF sensor and remove the rubber cover from the MAF sensor connector.
3. Using an ohmmeter, make the following measurements at the MAF sensor connector:
   • Terminal B and ground — less than 10 ohms.
   • Terminal BR and ground — less than 10 ohms.

   NOTE: If resistance is greater than 10 ohms, check the harness and internal circuits of the control unit for discontinuity and/or the ground terminal on the intake manifold for poor contact.

4. Switch the ignition ON and connect the electrical wiring to the MAF sensor.
5. Using a voltmeter, measure the voltage between the R terminal of the MAF sensor connector and ground; it should be 10V or more.

   NOTE: If the voltage is not within specifications, check the condition of the battery, fuse, control unit harness and/or connector in the power line.

6. Using a voltmeter, measure the voltage between the W terminal and the BR terminal of the MAF sensor connector; it should be 1–2V.

   NOTE: If the voltage is not within specifications, replace the mass airflow sensor.

7. Disconnect MAF sensor from air cleaner.
8. Blow air through the MAF sensor, from the air cleaner side, while measuring the voltage between the W terminal and the BR terminal of the MAF sensor connector. If the reading is not 1–2V, replace the mass airflow sensor.
9. Install the MAF sensor onto the air cleaner.
10. Start and warm the engine.
11. Drive the vehicle at 15 mph for at least 1 minute.
12. Rev the engine above 2000 rpm and allow it to idle.
13. Using a voltmeter, measure the voltage between the light red wire terminal of the MAF sensor and ground; it should be 0V.
14. Turn the ignition switch OFF.
15. Using a voltmeter, measure the voltage, within 1 second after turning the engine OFF, between the light red wire terminal of the MAF sensor and ground; it should be 12V.

    NOTE: If the voltage is not within specifications, check the harness from the control unit to the MAF sensor for discontinuity.

Loyale

1. Remove the MAF sensor. Inspect the air boot and check for leaks.
2. Inspect for obvious signs of contamination such as dust, dirt, water and other foreign matter. Clean out any contamination found.
3. Install the MAF sensor and unplug the connector. Switch the ignition OFF.
4. Measure the resistance between terminal BR and ground. If resistance exceeds 10 ohms, check the harness for proper continuity and ground terminal on the intake manifold for poor contact.
5. Switch the ignition ON but do not start the engine.
6. Plug the MAF sensor connector back in and measure voltage between terminal SA and ground. It should be at least 10 volts. If not, check the power feed circuit for poor connections, melted fuses, etc.
7. Connect voltmeter positive (+) lead to terminal SA and voltmeter negative (-) lead to terminal BR. Measure the voltage; it should be 1–2 volts. Replace the MAF sensor if not within 1–2 volts.

Impreza

1. Turn the ignition ON.
2. Backprobe ECU connector terminal B5 with a high-impedance voltmeter.
3. If the voltage is more than 0.3 volt, check the wiring between terminal B5 and the MAF sensor.
4. If the voltage is less than 0.3 volt, substitute a known good ECU and retest.
5. Backprobe ECU terminal C1 with a high-impedance voltmeter. The voltage should be 0 volts.
6. If the voltage is more than 0 volts, check for a short between C1 and a voltage carrying wire.
7. If no short is present, substitute a known good ECU and retest.
8. Start the engine and backprobe terminal B5 on the ECU. The voltage should be between 0.8–1.2 volts.
9. If the voltage is not within 0.8–1.2 volts, repair wiring between terminal B5 of the ECU and the MAF sensor.
10. If voltage is within 0.8–1.2 volts, continue testing to next step.
11. Backprobe terminal C1 on the ECU. The voltage should be 0 volts.
12. If voltage is present, inspect terminal C1 wiring to the MAF sensor for a short to voltage.
13. If no short is present, substitute a known good ECU and retest.
14. Turn the ignition switch OFF and unplug the MAF sensor. Turn the ignition switch ON and check for system voltage at terminal 1 of the MAF connector.
15. If voltage is not present, repair wiring.
16. If voltage is present, continue testing to next step.
17. Turn the ignition switch OFF and unplug the ECU connector. Check all wiring between the ECU and the MAF sensor for shorts, opens and ground. Repair as required.
18. If the wires check out OK, replace the MAF sensor.

Legacy

1. Unplug the MAF sensor connector.
2. Measure the resistance between the MAF sensor terminals and chassis ground.
3. Terminals 1, 2 and 4 should have 1 mega-ohm of resistance to ground.
4. Terminal 3 should have 0 ohms to ground.
5. Replace the MAF sensor if any of the resistance readings are out of range.

SVX

1. Switch the ignition ON.
2. Take the following voltage readings:
3. Measure the voltage between terminal 10 and body ground; it should be between 10–13 volts.
4. Measure the voltage between terminal 5 and body ground; it should be between 0–0.3 volt.
5. Measure the voltage between terminal 6 and body ground; it should be 0 volts.
6. Start the engine and take the following readings:
7. Measure the voltage between terminal 11 and body ground; it should be 13–14 volts.
8. Measure the voltage between terminal 5 and body ground; it should be 0.8–1.2 volts.
9. Measure the voltage between terminal 6 and body ground; it should be 0 volts.
10. If any of the MAF readings is out of range, check the harness and power supply. If the readings are still out of range, replace the MAF sensor.