Yale 522120-1 – VSM or TCU: Engine RPM Higher than XMSN Limit

The system is detecting an engine speed that exceeds the allowable limit for the transmission's current state. This is typically caused by a faulty Engine RPM sensor, a faulty Transmission Speed Sensor, or a wiring issue causing a mismatch in speed readings.

• Yale and Hyster Forklifts
• 2005 and newer Yale and Hyster forklifts
• Yale VX series
• Yale GC135VX
• Yale GDP155VX
• Hyster FT series
• Hyster S155FT
• Hyster H40FTS
• Hyster S30FT
• Hyster S40FTS

1. 1

   Inspect the wiring harnesses for the Engine RPM sensor and the Transmission Speed Sensor (TISS/TOSS) for open circuits, bad crimps, or loose pins.

2. 2

   Perform a wiggle test with the key on near the sensors and the VSM/TCU to check for dropping connections or clicking components.

3. 3

   Use a multimeter to check sensor circuits for an open circuit in the 5V supply, signal open/short to ground, or signal shorted to battery.

4. 4

   If sensors and wiring test good, check for a functional failure within the VSM or TCU controller.

1. 1

   Power Down

   Turn off the forklift and disconnect the battery to ensure safety and prevent electrical shorts.

2. 2

   Locate the Sensors

   Locate the Engine RPM sensor on the engine block and the Transmission Speed Sensor (TISS/TOSS) on the transmission housing.

3. 3

   Repair Wiring

   If your diagnostic checks revealed a short, open circuit, or bad crimp, repair the damaged section of the wiring harness or replace the connector.

4. 4

   Replace the Sensor

   If the wiring is intact, replace the suspect sensor. For the transmission speed sensor, remove the capscrew and lock washer, then pull the sensor from the transmission. Install the new sensor and secure the hardware.

5. 5

   Reassemble and Power Up

   Reconnect the sensor plugs and reconnect the battery.

6. 6

   Clear Codes

   Clear the fault history logs using the DSC (Display Switch Cluster) or the appropriate diagnostic software.

7. 7

   Test Operation

   Start the forklift and test drive it through its forward and reverse ranges to ensure the engine RPM and transmission speed synchronize correctly and the code does not return.