What is Yanmar General Fault Code P0222-4?

Fault Code P0222-4 indicates a Throttle Position Sensor B (TPS B) Circuit Low Voltage condition with specific severity level 4. This diagnostic trouble code means the Engine Control Module (ECM) has detected an abnormally low voltage signal from the secondary throttle position sensor circuit, falling below the manufacturer's specified threshold (typically below 0.2-0.5 volts).

In Yanmar diesel engines, the throttle position sensor provides critical feedback to the ECM regarding accelerator pedal position and engine load demand. The "B" designation refers to the redundant or secondary TPS circuit, which Yanmar employs for fail-safe operation and signal validation. When this sensor reports voltage outside normal parameters, the ECM cannot accurately determine operator intent, leading to performance limitations and potential derate modes to protect the engine. For used excavators, this code is particularly concerning as it directly affects throttle response, power output, and overall machine productivity.

Common Symptoms

• Reduced engine power or activation of limp mode, limiting machine to idle or low RPM operation
• Erratic throttle response where the engine doesn't respond proportionally to accelerator pedal input
• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Intermittent stalling or failure to increase RPM under load during digging or lifting operations
• Error messages displayed on the machine's monitor indicating throttle system malfunction

Potential Causes

• Damaged or corroded wiring harness connections at the TPS connector, especially common in used machines exposed to moisture and vibration
• Failed Throttle Position Sensor B, often due to internal wear, contamination, or component age exceeding service life
• Chafed or pinched wiring along the harness routing points where cables contact frame members or move with the pedal linkage
• Poor ground connection at the sensor or ECM, creating voltage drop and false low readings
• ECM internal fault (less common) where the input circuit itself has failed or sustained damage
• Corroded connector pins at the TPS plug, particularly in machines operated in wet, muddy, or marine environments

How to Troubleshoot and Fix Code P0222-4

Step 1: Visual Inspection of Sensor and Harness Begin by locating the throttle position sensor assembly on the fuel injection pump or electronic throttle body. Inspect the electrical connector for corrosion, bent pins, moisture intrusion, or physical damage. On used excavators, pay special attention to harness routing—check for wire chafing against brackets, evidence of previous repairs with electrical tape, or heat damage near engine components.

Step 2: Perform Voltage and Resistance Testing Disconnect the TPS connector and use a digital multimeter to measure resistance across the sensor B circuit terminals (consult Yanmar wiring diagrams for specific pin identification). Typical resistance should range between 1-5 kΩ depending on throttle position. With ignition ON and sensor connected, backprobe the signal wire to measure voltage—it should read approximately 0.5-4.5 volts and change smoothly as the throttle is actuated. A reading stuck near zero volts confirms low voltage condition.

Step 3: Check Wiring Continuity and Ground Integrity Test continuity between the TPS connector and the ECM harness connector to identify any open circuits or high-resistance connections. Measure voltage drop on the ground circuit with the ignition on—it should be less than 0.1 volts. For used machines, remove connectors and apply dielectric grease after cleaning to prevent future corrosion.

Step 4: Component Replacement and Verification If sensor and wiring tests confirm failure, replace the Throttle Position Sensor B with a genuine Yanmar part or quality OEM equivalent. After installation, clear fault codes using Yanmar diagnostic software or a compatible scan tool. Perform a throttle relearn procedure if required by the system, then test under load to verify proper operation and confirm code does not return.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Yanmar service manual for your specific model and serial number. If you're uncomfortable performing electrical diagnostics, contact a certified Yanmar technician or qualified diesel mechanic to prevent further damage to your excavator's electronic systems.