What is Sany Excavator Fault Code P108?

Fault Code P108 indicates a manifold air pressure (MAP) sensor circuit voltage is too high or out of expected range. This diagnostic trouble code (DTC) is triggered when the engine control module (ECM) detects an abnormally high voltage signal from the MAP sensor, which monitors intake manifold absolute pressure to optimize fuel injection and engine performance.

The MAP sensor is critical for Sany excavators because it provides real-time data to the ECM about engine load conditions. When this sensor fails or sends incorrect voltage readings, the ECM cannot accurately calculate air-fuel ratios, leading to reduced performance, increased emissions, and potential engine damage. In used excavators, this code often appears due to sensor degradation, wiring issues, or connector corrosion from years of exposure to harsh construction environments.

Common Symptoms

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the dashboard
• Noticeable loss of engine power or throttle response, especially under heavy loads
• Rough idling or unstable engine RPM at startup or during operation
• Black smoke from the exhaust indicating overly rich fuel mixture
• Difficulty starting the engine, particularly in cold weather conditions

Potential Causes

The most common technical causes for P108 in Sany excavators include:

• Damaged or corroded MAP sensor connector due to moisture intrusion or age-related wear
• Failed MAP sensor itself, often caused by internal diaphragm rupture or electronic component failure
• Shorted or damaged wiring harness between the MAP sensor and ECM, particularly at rub points near the engine block
• Faulty ECM ground connection causing voltage reference issues
• Vacuum hose leaks or blockages affecting manifold pressure readings
• Previous aftermarket repairs using incorrect sensor specifications

How to Troubleshoot and Fix Code P108

Step 1: Visual Inspection Locate the MAP sensor (typically mounted on the intake manifold). Inspect the electrical connector for corrosion, bent pins, or moisture. Check the wiring harness for visible damage, especially where it contacts hot engine components or sharp edges—common wear points in used equipment.

Step 2: Voltage Testing Using a digital multimeter, backprobe the MAP sensor connector with the ignition on but engine off. Check for proper 5-volt reference signal from the ECM. Compare readings against Sany service manual specifications (typically 4.5-5.2 volts). Test the ground circuit for continuity and ensure less than 0.1-ohm resistance.

Step 3: Sensor Output Testing With the engine running, measure the MAP sensor output voltage at idle (should read approximately 1-2 volts) and under load. If voltage remains above 4.5 volts regardless of engine condition, replace the sensor.

Step 4: Harness and ECM Verification If sensor tests normal, inspect the entire wiring harness for shorts to positive voltage. Check ECM connector terminals for corrosion. For used excavators, remove protective loom and physically examine wires for insulation breakdown—a frequent issue after 5,000+ operating hours.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with high-voltage systems.