JCB P2138 – ECU: Hand Pedal Signal Correlation Fault

The Engine Control Unit (ECU) has detected a discrepancy between the two separate position signals generated by the hand throttle position sensor. In this electronic throttle system, the ECU continuously compares the voltage signals from these independent sensors for redundancy and safety. If the signals do not match a pre-defined expected correlation, the ECU flags the inconsistency, preventing it from accurately determining the desired throttle position and triggering a fail-safe mode to prevent unintended acceleration.

• Tier 4i engines
• Tier 4 Final (T4i/T4F) engines
• JS Series Tracked Excavators
• JZ Series Tracked Excavators
• 806X Mini Excavators
• 808X Mini Excavators
• EcoMAX engine range
• JS130
• JS200
• JS220
• JS230

1. 1

   Carefully inspect the wiring harness and connectors associated with the hand throttle position sensor. Look for any signs of damage, such as chafing, pinching, or stretching of the wires. Check for loose connector pins, corrosion, or water/debris inside the connector terminals, which can occur from pressure washing or exposure to the elements.

2. 2

   Use a compatible diagnostic tool, such as JCB Service Master, to check for any other active or stored fault codes. Repairing other related faults first may resolve the P2138 code.

3. 3

   With the machine's ignition on, gently wiggle the connectors and wiring harness for the hand throttle sensor while observing the live data on a scan tool. If the signal fluctuates or drops out, it indicates an intermittent connection or wiring fault.

4. 4

   Verify if any manufacturer service bulletins or recalls exist for the specific machine model related to this fault code.

1. 1

   Safety First and Connector/Wiring Service

   Stop the engine and allow it to cool. Disconnect the machine's battery before starting any electrical repairs. Disconnect the hand throttle position sensor connector. Clean the connector pins and terminals using a suitable electrical contact cleaner. Check for any backed-out pins or poor crimps. After cleaning, apply dielectric grease to the connector seal to prevent future moisture ingress. Repair any damaged sections of the wiring harness.

2. 2

   Sensor Voltage Test

   With the ignition on and the engine off, use a multimeter to measure the voltage of the two signal wires from the hand throttle sensor. Both signals should show a smooth and proportional change in voltage as the hand throttle is moved from the minimum to the maximum position. While the two signals will not be identical, they should maintain a consistent correlation. Any sudden spikes, drops, or flat spots in the voltage reading indicate a faulty sensor.

3. 3

   Component Replacement

   If the sensor is determined to be faulty, it must be replaced. Ensure the replacement part is a genuine OEM component or a high-quality equivalent.

4. 4

   Throttle Calibration

   After replacing the hand throttle sensor or throttle motor, a calibration procedure is often necessary to teach the ECU the new sensor's range of motion. Ensure the throttle dial is at its minimum position. Turn the ignition key to the 'ON' position without starting the engine. On some models, you may need to enter a specific calibration mode through the machine's display unit. Slowly and smoothly cycle the hand throttle from its minimum to maximum position and back again. This may need to be repeated two or more times. Turn the ignition off for at least 30 seconds to allow the ECU to save the new calibration settings.

5. 5

   Final Verification

   After completing the repair and calibration, clear all fault codes and start the machine. Operate the hand throttle to ensure smooth and correct engine response. Re-scan for any returning fault codes to confirm the repair was successful.