What is Yanmar General Fault Code P0222?

Fault Code P0222 indicates a Throttle Position Sensor/Pedal Position Sensor B Circuit Low Input. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally low voltage signal from the secondary throttle position sensor circuit, typically below 0.17 volts for more than one second.

In Yanmar excavators, the Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APPS) provides critical input to the ECM regarding operator throttle demand. This sensor typically uses two separate circuits (A and B) for redundancy and safety verification. When Circuit B reports voltage outside the expected range, the ECM cannot accurately determine engine load requests, compromising machine performance and potentially triggering limp mode to prevent damage. This is particularly critical in excavators where precise hydraulic control depends on accurate engine speed management.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the instrument panel
• Engine derate or limp mode activation, limiting maximum RPM to approximately 1500-2000 RPM
• Poor throttle response or complete loss of throttle control from the pedal/lever
• Erratic engine behavior, including surging, hesitation, or inability to increase engine speed under load
• Secondary fault codes may appear related to fuel system or governor control

Potential Causes

The most common technical causes for P0222 in used Yanmar excavators include:

• Faulty throttle position sensor or accelerator pedal sensor, particularly due to internal wear, contamination, or potentiometer track degradation
• Damaged or corroded wiring harness, especially at flex points near the pedal assembly or where harnesses route along the chassis
• Loose, corroded, or oil-contaminated electrical connectors at the sensor or ECM
• Broken or chafed wires in Circuit B, often caused by rubbing against sharp edges or movement over time
• Poor ground connection affecting sensor reference voltage
• ECM internal fault (less common, but possible in high-hour machines)
• Low supply voltage from damaged power supply circuits feeding the sensor

How to Troubleshoot and Fix Code P0222

Step 1: Visual Inspection Begin with a thorough visual examination of the throttle/accelerator pedal sensor and its wiring harness. On used excavators, check for obvious damage, worn insulation, oil contamination on connectors, and corrosion. Inspect harness routing for rub points against metal edges, particularly where wires flex during operation.

Step 2: Electrical Testing Using a digital multimeter (DMM), backprobe the sensor connector while connected. Check the supply voltage (typically 5 volts) and ground continuity. Then measure the signal voltage on Circuit B while slowly moving the throttle—it should sweep smoothly from approximately 0.5V to 4.5V. A reading stuck below 0.5V confirms the low input condition.

Step 3: Resistance and Continuity Checks Disconnect the sensor and measure resistance across the potentiometer while moving the throttle (typically 1-5 kΩ range, check Yanmar specifications). Test wire continuity from sensor connector to ECM harness connector. Resistance should be less than 5 ohms; infinite resistance indicates an open circuit.

Step 4: Component Replacement If testing confirms sensor failure, replace the throttle position sensor or pedal assembly with OEM or quality aftermarket parts. For used machines, always replace the connector pigtail if corrosion is present. Clear codes with Yanmar diagnostic software and perform relearn procedures if required.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Yanmar service manual for your specific model and consider professional assistance for complex electrical diagnostics.