Signal Too Low. Permanent Fault

Checking Fresh Air Intake
- Ignition off.
- Check that the fresh air intake is intact and properly connected.
- Is the fresh air intake intact?

Yes:
^ Proceed to test step below.

No:
^ Remedy as necessary.
^ Then proceed to Verification section below.





Checking Power Cable
- Ignition off.
- Disconnect mass air flow (MAF) sensor.
- Ignition on.
- Connect a voltmeter between mass air flow sensor connector terminal 3 and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between mass air flow sensor terminal 3 and main relay (2/32) terminal 3 for an open-circuit.
^ Then proceed to Verification section below.





Checking Signal Cable
- Ignition off.
- Wait approx. 150 seconds.
- Mass air flow sensor disconnected.
- Connect an ohmmeter between mass air flow sensor connector terminal 4 and ground.
- The ohmmeter should read approx. 9 - 11K ohms.

If reading is OK:
^ Proceed to test step below.

If value is lower:
^ Check cable between mass air flow sensor terminal 4 and engine control module (ECM) # A4 for a short-circuit to ground.
^ Then proceed to Verification section below.

If value is higher:
^ Check cable between mass air flow sensor terminal 4 and engine control module # A4 for an open-circuit.
^ Then proceed to Verification section below.





Checking Mass Air Flow Sensor Signal
- Ignition off.
- Connect the mass air flow sensor.
- Ignition on.
- Connect a voltmeter between mass air flow sensor connector terminals 4 and 2.
- The voltmeter should read approx. 0.1 - 0.2 Volts.

If reading is OK:
^ The cause of the diagnostic trouble code (DTC) is poor contact in the mass air flow sensor and/or the engine control module connector. Check connectors for contact resistance and oxidation and remedy.
^ Then proceed to Verification section below.

If reading is incorrect:
^ Try a new mass air flow sensor.
^ Then proceed to Verification section below.





Verification
- After carrying out the repair, check that the fault has been remedied as follows.
- Ignition off.
- Reconnect connectors, reinstall components etc.
- Start the engine and idle it for a few minutes.
- Read off diagnostic trouble codes.
- If EFI-121 is stored it should have the status intermittent fault.

If reading is OK:
^ Fault corrected.

If reading is incorrect:
^ Proceed to test step below.

Fault-tracing Information
The verification result shows that the fault persists.

- Do you want to exit fault-tracing?

Yes:
^ Fault not corrected.

No:
^ Return to Checking Fresh Air Intake section above.