John Deere 177.04 – CCU, TCU, EPC, PTP, BIF: Transmission Oil Temperature Sensor Voltage Too Low

The control unit detects an abnormally low voltage on the transmission oil temperature sensor circuit (B60), which almost always indicates a short to ground. Because of the shorted circuit, the system receives a false reading indicating that the transmission oil temperature is extremely high (e.g., above 125°C / 257°F).

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6M Series
• 6MC Series
• 6RC Series
• 6090MC
• 6100MC
• 6010 to 6910 Series
• 9030 Series
• 9230
• 9330
• 9430
• 9530
• 9630
• 5G Specialty Tractors
• 210L EP Tractors
• 450J Crawler Dozer
• 550J Crawler Dozer
• 650J Crawler Dozer
• 310G/J/K Backhoe Loader
• 410G/J/K Backhoe Loader
• 710G/J/K Backhoe Loader

1. 1

   Inspect the sensor circuit wiring harness from the transmission oil temperature sensor (B60) back to the control module for pinched wires, melted insulation, or rubbing that could cause a short to ground.

2. 2

   Disconnect the sensor and inspect the connector pins for corrosion, moisture, and debris.

3. 3

   Perform a disconnect test: with the machine on, disconnect the sensor. If the fault code changes from 177.04 (Voltage Too Low) to 177.03 (Voltage Too High / Open Circuit), the wiring harness and control module are functioning correctly, proving the sensor itself is internally shorted.

4. 4

   Measure sensor resistance across the pins using a multimeter. A dead short (0 ohms) confirms a failed sensor. A healthy sensor reads roughly 979 Ohms at 50°C and 670 Ohms at 60°C.

1. 1

   Prepare machine

   Park the machine on a level surface, engage the parking brake, turn off the engine, and remove the key.

2. 2

   Locate sensor

   Locate the Transmission Oil Temperature Sensor (B60) on the transmission housing (consult your specific model's parts diagram for exact placement).

3. 3

   Clean area

   Thoroughly clean the area around the sensor to prevent dirt from entering the transmission.

4. 4

   Disconnect harness

   Disconnect the electrical harness connector from the sensor.

5. 5

   Place drain pan

   Place a clean drain pan directly underneath the sensor. A small amount of hydraulic/transmission oil will likely escape when the sensor is removed.

6. 6

   Remove faulty sensor

   Using a deep socket or wrench, unscrew and remove the faulty sensor.

7. 7

   Prepare new sensor

   Prepare the new sensor. Ensure the sealing O-ring is installed on the new sensor (some part numbers require the O-ring to be purchased separately).

8. 8

   Install new sensor

   Thread the new sensor into the transmission housing and tighten to the OEM torque specification.

9. 9

   Reconnect harness

   Reconnect the electrical harness, ensuring it clicks securely into place.

10. 10

    Check oil level

    Check the transmission oil level via the dipstick or sight glass and top up any fluid lost during the swap.

11. 11

    Verify repair

    Turn the key to the ON position, clear the stored fault codes from the CCU/TCU, and start the machine to verify the code does not return.