What is XCMG QSB4.5 CM2150 B108 Fault Code 124?

Fault Code 124 indicates an Intake Manifold Pressure (Boost Pressure) Sensor circuit voltage is above the normal operating range on the Cummins QSB4.5 CM2150 engine used in XCMG excavators. This code triggers when the Engine Control Module (ECM) detects a signal voltage from the intake manifold pressure sensor that exceeds manufacturer-specified thresholds, typically above 4.8-5.0 volts.

The boost pressure sensor is critical for proper engine performance on turbocharged diesel engines like the CM2150. It monitors intake manifold pressure and sends real-time data to the ECM, which adjusts fuel delivery and turbocharger operation accordingly. When this sensor reports incorrect high voltage, the ECM cannot accurately regulate air-fuel ratios, potentially causing performance issues, increased emissions, and engine protection modes.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the instrument panel
• Engine derate mode activated, limiting power output to 50-75% of normal capacity to protect components
• Black smoke from exhaust due to improper fuel-to-air ratio calculations
• Poor throttle response or hesitation during acceleration under load
• Rough idle or unstable engine RPM, particularly noticeable during hydraulic operations

Potential Causes

The most common technical causes for Code 124 on used XCMG excavators include:

• Open circuit or damaged wiring harness between the boost pressure sensor and ECM—particularly at harness routing points near the engine block where vibration causes wire chafing
• Corroded or loose electrical connectors at the sensor due to moisture intrusion (common on older machines with deteriorated seals)
• Failed intake manifold pressure sensor with internal short circuit causing constant high voltage output
• ECM internal fault affecting the 5-volt reference circuit (less common but possible on high-hour machines)
• Damaged sensor mounting causing vacuum leaks that affect readings

How to Troubleshoot and Fix Code 124

Step 1: Visual Inspection Perform a thorough inspection of the boost pressure sensor (located on the intake manifold near the turbocharger outlet) and its wiring harness. On used excavators, check specifically for connector corrosion, damaged pins, or harness abrasion against metal edges. Inspect the sensor mounting for cracks or loose fittings.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure voltage at the ECM side of the harness. You should see approximately 5.0 volts on the reference wire (with ignition on, engine off). Check for continuity on the ground and signal wires. Resistance testing at the sensor should show 100-300 ohms (consult service manual for exact specifications).

Step 3: Sensor and Harness Replacement If voltage readings are correct but the code persists, replace the intake manifold pressure sensor with an OEM or quality aftermarket unit. For used machines with over 5,000 hours, consider replacing the entire sensor harness section if any signs of wear, heat damage, or previous repairs are evident—this prevents recurring failures.

Step 4: ECM Verification Clear codes using Cummins Insite diagnostic software or compatible scan tool and perform a test run. If Code 124 returns immediately without load, suspect ECM internal circuit failure requiring professional ECM testing or replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult the XCMG service manual and Cummins engine documentation for your specific machine. For complex electrical diagnostics or ECM programming, contact a certified Cummins technician or XCMG dealer.