JCB P2138 – Engine ECU: Hand Pedal Signal Mapping Failure

The system has detected a failure in the mapping of the hand pedal signal, indicating a correlation fault between the two position signals generated by the hand throttle position sensor. Modern electronic throttle systems use this dual-signal setup for redundancy and safety. When these signals do not agree or are not properly interpreted by the system, the Engine ECU cannot verify the true throttle position and logs this fault. This typically forces the machine into a 'limp home' mode, resulting in reduced engine power or limiting the engine to idle speed only.

• Loadall Telescopic Handlers
• 3CX Backhoe Loader
• 4CX Backhoe Loader
• 5CX Backhoe Loader
• Tracked Excavators
• Wheeled Excavators

1. 1

   Stop the engine, allow it to cool, and visually inspect the hand throttle wiring harness for chafing, cuts, or heat damage.

2. 2

   Check the harness connectors for physical damage and ensure they are securely connected.

3. 3

   Disconnect the sensor and inspect the connector terminals for debris, corrosion, or water ingress, which can result from pressure washing or poor seals.

4. 4

   Verify that machine earth points are secure and clean.

5. 5

   Check sensor power supply at the connector (harness disconnected, ignition on): Pins 1 and 4 should read 5 volts; Pins 3 and 6 should be at ground (0 volts). If the voltage is incorrect, check the wiring harness for continuity and inspect the ECU pins for dirt or corrosion.

6. 6

   Check signal voltage (ignition on): Pin 2 should read between 4.0 to 4.5 volts; Pin 5 should read between 2.2 to 2.5 volts.

7. 7

   Use a diagnostic tool (e.g., JCB ServiceMaster) to graph live data for both sensor signals while operating the hand throttle. Voltage should rise smoothly and proportionally from approximately 0.5V to 4.5V. A sudden spike or drop in one of the signals indicates a fault with the sensor or wiring.

1. 1

   Confirm fault

   Use the diagnostic checks to confirm that the hand throttle sensor or its wiring is the root cause, ruling out intermittent connection issues.

2. 2

   Disconnect power

   Disconnect the machine's battery to prevent electrical shorts during repair.

3. 3

   Access the sensor

   Locate the hand throttle position sensor under the front console in the operator's cab. Remove any necessary panels or covers for access.

4. 4

   Remove faulty sensor

   Disconnect the electrical connector from the hand throttle assembly and remove the mounting bolts or screws securing it to the console.

5. 5

   Install new assembly

   Mount the new hand throttle assembly, ensure it is securely fastened, and reconnect the electrical connector.

6. 6

   Clear codes

   Reconnect the battery and use a diagnostic scanner to clear the P2138 fault code from the Engine ECU.

7. 7

   Test operation

   Start the machine and test the hand throttle to ensure it functions correctly and the fault code does not reappear.