Massey Ferguson D191 – Instrument Panel / Dash (Module X55): Pneumatic brake system pressure sensor (Sensor X168) - Electrical signal too high.

The controller is receiving a voltage signal from the air brake pressure sensor that exceeds the normal operating range, typically pointing to a short circuit to power (VCC), a broken ground wire, or an internally shorted sensor.

• MF 8650
• MF 8680
• Interim Tier 4 (2012-2015)
• 7615
• 5613
• MF 8480
• MF 8450
• 7616
• 7618
• 5608
• 7619
• 7626
• MF 8660
• 7624
• MF 8690
• 7614
• MF 8470
• 5610
• 7620
• MF 8600
• MF 8460
• MF 8670
• 5612
• 7622
• 5611
• 5609
• MF 7600 Series
• MF7600
• MF 7700 / 7700S Series Tier 4
• 7714
• 7715
• 7716
• 7718
• 7719
• 7720
• 7722
• 7724
• 7726
• MF 8600 Series
• 8670
• 8690
• Dyna-4 and Dyna-6 Transmission Models
• 5400 series
• 6400 series

1. 1

   Visually inspect the pneumatic brake pressure sensor (X168) housing and wiring harness connector for physical damage, moisture ingress, or corrosion.

2. 2

   Check the signal wire for a short to voltage (VCC) by disconnecting the sensor, turning the key ON, and measuring the voltage on the signal wire to ensure it isn't shorted to the 5V reference or 12V battery power.

3. 3

   Verify the sensor has a solid ground connection back to the instrument panel/chassis, as a broken or highly resistant ground wire will cause the signal voltage to default high.

4. 4

   If the reference voltage, signal, and ground wiring test good from the sensor connector back to the X55 Instrument Panel, bench test the sensor to confirm if it has failed internally and is bleeding reference voltage into the signal circuit.

1. 1

   Depressurize the System

   Turn off the tractor and safely bleed all compressed air from the pneumatic brake system reservoirs to prevent injury when removing the sensor.

2. 2

   Disconnect the Sensor

   Unplug the electrical connector from the X168 air brake pressure sensor.

3. 3

   Remove the Sensor

   Using a wrench, unthread the faulty pressure sensor from the air line/valve block.

4. 4

   Install the New Sensor

   Apply a thread sealant (if not pre-applied to the new sensor) and thread the new sensor into the port. Tighten to the manufacturer's specified torque (do not over-tighten, as this can damage the pneumatic block).

5. 5

   Reconnect and Test

   Plug the electrical harness back in. Start the tractor, allow the air compressor to build system pressure, and check for air leaks with soapy water.

6. 6

   Clear Codes

   Use the tractor's DOT Matrix keyboard/diagnostic menu or a dealer diagnostic tool to clear the stored D191 fault code from the Instrument Panel (X55) memory.