Signal Too High. Permanent Fault

Checking Power Ground
- Ignition OFF.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Disconnect mass air flow (MAF) sensor.
- Connect an ohmmeter between mass air flow sensor connector terminal 1 and ground.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to: Checking Signal Ground section below.

If reading is incorrect:
^ Proceed to: Checking Engine Control Module Connector section below.





Checking Engine Control Module Connector
- Ignition OFF.
- Mass air flow sensor disconnected.
- Check engine control module (ECM) connector for contact resistance and oxidation.
- Engine control module connected.
- Connect an ohmmeter between mass air flow sensor connector terminal 1 and ground.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to: Checking Signal Ground section below.

If reading is incorrect:
^ Check cable between mass air flow sensor terminal 1 and engine control module # A3 for an open-circuit.
^ Proceed to: Verification section below.





Checking Signal Ground
- Ignition OFF.
- Mass air flow sensor disconnected.
- Connect an ohmmeter between mass air flow sensor connector terminal 2 and ground.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to: Checking Signal Cable section below.

If reading is incorrect:
^ Proceed to: Checking Engine Control Module Connector section below.





Checking Engine Control Module Connector
- Ignition OFF.
- Mass air flow sensor disconnected.
- Check engine control module connector for contact resistance and oxidation and remedy.
- Engine control module connected.
- Connect an ohmmeter between mass air flow sensor connector terminal 2 and ground.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to: Checking Signal Cable section below.

If reading is incorrect:
^ Check cable between mass air flow sensor terminal 2 and engine control module # A5 for an open-circuit.
^ Proceed to: Verification section below.





Checking Signal Cable
- Ignition ON.
- Mass air flow sensor disconnected.
- Connect a voltmeter between mass air flow sensor connector terminal 4 and ground.
- The voltmeter should read 0 - 1 Volts.

If reading is OK:
^ Proceed to: Checking Mass Air Flow Sensor Signal section below.

If reading is incorrect:
^ Check cable between mass air flow sensor terminal 4 and engine control module # A4 for a short-circuit to supply voltage.
^ After remedying fault, Proceed to: Checking Mass Air Flow Sensor section below.





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

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

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





Checking Mass Air Flow Sensor
The mass air flow sensor may fail if there has been a short-circuit to supply voltage in the signal cable. Check mass air flow sensor as follows:

- Ignition OFF.
- Connect mass air flow sensor.
- Ignition ON.
- Connect a voltmeter between mass air flow sensor connector terminals 2 and 4.
- The voltmeter should read 0.1 - 0.2 Volts.

If reading is OK:
^ Mass air flow sensor is OK.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Try a new mass air flow sensor.
^ 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 minute.
- Read off any diagnostic trouble codes.
- If EFI-121 is stored, it should have intermittent fault status.

If reading is OK:
^ Fault corrected

If reading is incorrect:
^ Proceed to: Fault-tracing Information section below.

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

- Do you want to exit fault-tracing?

Yes:
^ Fault not corrected.

No:
^ Proceed to: Checking Power Ground section above.