Massey Ferguson 171.04 – Engine Control Unit (ECU): Ambient Temperature Sensor Voltage Issue (ECU)

Ambient temperature sensor voltage below normal. The input voltage in the ambient air temperature sensor circuit drops to a level outside its normal operating range, most likely due to a short to ground in the sensor or its wiring harness.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724

1. 1

   Visual Inspection: Inspect the wiring harness leading to the ambient temperature sensor (usually located near the front intake/grille area). Look for chafed wires, melted insulation, or pinched lines that could cause a short to ground.

2. 2

   Connector Check: Disconnect the sensor and inspect the pins on both the sensor side and the harness side for corrosion, moisture, or bent pins.

3. 3

   Voltage/Ground Test: With the sensor disconnected and the key ON, use a multimeter to check the reference voltage from the ECU at the harness connector. Test the ground circuit for continuity.

4. 4

   Sensor Resistance Test: Measure the internal resistance of the ambient temperature sensor. If it reads as a dead short (zero or near-zero ohms), the sensor has failed internally and must be replaced.

1. 1

   Turn off the tractor ignition and disconnect the negative battery terminal to protect the ECU.

2. 2

   Locate the ambient temperature sensor at the front of the machine.

3. 3

   Depress the locking tab and disconnect the electrical pigtail from the sensor.

4. 4

   If the diagnostic checks revealed a wiring short, repair the damaged section of the harness using heat-shrink butt connectors and re-loom the wire.

5. 5

   If the sensor itself is internally shorted, unbolt or unclip the faulty sensor from its mounting bracket.

6. 6

   Install the new OEM ambient temperature sensor and secure it.

7. 7

   Reconnect the electrical harness, ensuring the weather-pack seal clicks firmly into place.

8. 8

   Reconnect the battery.

9. 9

   Turn the key to the ON position and use a diagnostic scan tool to clear the 000171.04 code from the Engine ECU.

   Start the tractor and verify the code does not return.