Yale 177-4 – TCU (Transmission Control Unit) or VSM (Vehicle System Manager): Transmission Oil Temperature Sensor OORL (Out Of Range Low)

This fault code indicates that the signal voltage from the transmission oil temperature sensor is falling below the normal operating range. The underlying condition is typically an open circuit, a short to ground in the wiring, an internal sensor failure, or a controller input failure.

• Yale and Hyster Forklifts
• Yale VX series
• GLC050VX
• GLP080VX
• GDP40VX
• Hyster FT series

1. 1

   Inspect the transmission oil temperature sensor wiring harness and connectors for physical damage, corrosion, or exposed wires (especially right at the connector).

2. 2

   Check the wiring for an open circuit or a short to ground.

3. 3

   Test the sensor's resistance and signal voltage under operating temperatures using a multimeter or diagnostic equipment to check for internal failure.

4. 4

   Check the transmission fluid level and condition, and ensure the transmission case breather is clean to rule out overheating causes.

1. 1

   Repair Wiring

   If the diagnostic inspection reveals exposed wires or corrosion at the sensor connector, repair the wiring harness or replace the pigtail connector.

2. 2

   Replace Sensor

   If the wiring is intact but the sensor fails the resistance/voltage test, drain the transmission fluid (if required by the sensor location) and replace the Transmission Oil Temperature Sensor.

3. 3

   Test Controller

   If both the wiring and the sensor are confirmed to be in good working order, use diagnostic tools to test the controller's sensor input circuitry. If the controller is failing to read the signal, the TCU/VSM may need to be repaired or replaced.

4. 4

   Service Transmission

   If the forklift is near its transmission service interval (e.g., 2,000 hours), perform a full transmission fluid and filter service.

5. 5

   Clear Codes

   Once the repair is complete, use the onboard dash menu or diagnostic software (such as Jaltest) to clear the fault code and test-operate the forklift to ensure the code does not return.