Yale 177-3 – Transmission Control Unit (TCU) / Transmission ECM: Transmission Oil Temperature Sensor OORH (Out Of Range High)

This fault code indicates that the controller has detected the signal voltage from the transmission oil temperature sensor is above the normal operating range. This condition is typically caused by an open circuit in the wiring harness, a signal wire shorted to a 5V reference or battery voltage, or an internal failure of the sensor itself due to heat or wear.

• Yale and Hyster Forklifts
• Yale and Hyster forklifts (2005 and newer models)
• Yale VX series (e.g., GDP070VXNY)
• Hyster FT series (e.g., S30FT, H3.0FT)

1. 1

   Inspect the transmission wiring harness, the lower cab wiring harness, and the sensor connectors for physical damage, corrosion, or loose connections.

2. 2

   Compare the cluster gauge reading to an infrared thermometer pointed directly at the transmission sump to verify actual temperature.

3. 3

   Use a multimeter to perform open and short-circuit tests at each wiring harness connection, checking for shorts between the sensor signal wire and a 5V or battery voltage source.

4. 4

   Use diagnostic tools to check the sensor's resistance and signal voltages at operating temperatures to see if it is internally shorted.

1. 1

   Secure the Machine

   Park the forklift on a level surface, engage the parking brake, and disconnect the battery to prevent electrical shorts during repair.

2. 2

   Clean and Reseat Connectors

   Disconnect the transmission oil temperature sensor, clean the pins with contact cleaner, and securely reconnect it. Re-test to see if the code clears.

3. 3

   Repair Wiring

   If your multimeter tests reveal an open circuit or a short to a power source in the transmission or lower cab harness, repair or replace the affected section of the wiring.

4. 4

   Replace the Sensor

   If the wiring harness tests good but the sensor resistance is out of specification, remove the faulty transmission oil temperature sensor (sometimes referred to by technicians as the "whip transmission temperature sensor") and install a new OEM replacement.

5. 5

   Test the Controller

   If both the wiring and the sensor are in good working order, the fault lies within the controller's input circuitry. Test the TCU sensor inputs and repair or replace the controller as necessary.

6. 6

   Clear Codes

   Reconnect the battery, clear the diagnostic codes from the system, and monitor the live sensor data while running the machine to verify the fix.