Massey Ferguson 520390.31 – Engine Control Unit (ECU): Issue With The Air Intake Mass Air Flow Sensor (ECU)

Air mass sensor start test time exceeded or Air mass sensor start test value not plausible. The FMI 31 indicates that a condition exists where the sensor's initialization or self-test parameters are out of the expected range or taking too long to report back to the controller.

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• MF 8727 S
• MF 8730 S
• MF 8732 S
• MF 8735 S
• MF 8737 S
• MF 8740 S
• MF IDEAL 7
• MF IDEAL 8
• MF IDEAL 9
• MF 7370 ST5
• MF Beta 7370 PLI

1. 1

   Check for related MAF sensor codes (e.g., SPN 132 FMI 19, SPN 520384 FMI 14, or SPN 520382/520383 FMI 14) that might pinpoint the failure

2. 2

   Inspect the air intake system for blockages or severe restrictions, and check for code 107 FMI 18 (Air filter pressure below normal) which could indicate a clogged air filter

3. 3

   Inspect the wiring harness between the MAF sensor and the Engine ECU for chafed wires, corrosion in the connector pins, or loose connections

4. 4

   Verify the sensor is receiving the correct 5V reference supply from the ECU (check for codes 3509, 3510, or 3511 FMI 31 indicating 5Vdc supply out of range)

1. 1

   Power Down

   Turn off the machine and remove the key. Allow the engine and ECU to power down completely.

2. 2

   Locate the Sensor

   Locate the Mass Air Flow sensor on the main air intake pipe, typically positioned between the air filter housing and the turbocharger inlet.

3. 3

   Disconnect

   Carefully unplug the electrical connector from the MAF sensor.

4. 4

   Remove

   Loosen the retaining screws or clamps holding the MAF sensor in the intake duct and pull the sensor straight out.

5. 5

   Clean/Inspect

   If the sensor is heavily fouled with dust or oil, it may be cleaned with a dedicated MAF sensor cleaner as a temporary measure. However, if the internal circuitry has failed the start test, replacement is usually required.

6. 6

   Install New Sensor

   Insert the new OEM MAF sensor into the housing, ensuring the O-ring or gasket is seated properly to prevent unmetered air leaks. Secure the fasteners.

7. 7

   Reconnect

   Plug the electrical connector back in until it clicks.

8. 8

   Clear Codes

   Use a compatible diagnostic tool to clear the 520390.31 fault code from the Engine ECU. Start the engine and verify the code does not return during the ECU's start test phase.