What is Komatsu PC240LC-8 Fault Code CA155?

Komatsu PC240LC-8 Fault Code CA155 indicates a malfunction in the aftertreatment diesel particulate filter (DPF) differential pressure sensor circuit. This code specifically signals that the Engine Control Module (ECM) has detected an abnormal voltage or signal from the sensor that monitors pressure differences across the diesel particulate filter.

The differential pressure sensor measures the buildup of soot and particulate matter within the DPF by comparing inlet and outlet pressures. On the PC240LC-8, this sensor is critical for determining when regeneration cycles should occur and for protecting the aftertreatment system from excessive backpressure. When this sensor fails or provides incorrect readings, the ECM cannot properly manage DPF regeneration, potentially leading to reduced engine performance, increased fuel consumption, or even engine shutdown to prevent damage.

Common Symptoms

• Yellow engine warning light illuminated on the dashboard with possible DPF indicator light activation
• Reduced engine power or derate mode, limiting maximum RPM to protect the aftertreatment system
• Incomplete or failed automatic regeneration cycles, resulting in continued soot accumulation
• Increased exhaust backpressure causing sluggish throttle response and black smoke during operation
• Frequent forced regeneration requests or inability to initiate manual regeneration through the monitor panel

Potential Causes

The most common technical causes for Code CA155 on used PC240LC-8 excavators include:

• Failed differential pressure sensor due to carbon buildup, internal sensor diaphragm failure, or sensor element degradation (common after 5,000+ hours)
• Damaged or corroded wiring harness at connector pins, particularly where the harness routes near the exhaust system and experiences heat cycling
• Blocked or kinked pressure sensing tubes connecting the sensor to the DPF inlet and outlet ports
• ECM internal fault or corrupted calibration data affecting sensor signal interpretation
• Compromised connector seals allowing moisture intrusion into sensor electrical connections, especially on machines operated in wet or humid conditions
• Previous DPF service work where technicians improperly reconnected pressure lines or damaged sensor threads during filter cleaning

How to Troubleshoot and Fix Code CA155

Step 1: Visual Inspection of Sensor and Connections Locate the DPF differential pressure sensor mounted on the aftertreatment canister. Inspect the sensor body for physical damage, carbon deposits blocking pressure ports, or corroded electrical connectors. Check the pressure sensing tubes for kinks, cracks, or carbon plugging. For used excavators, pay special attention to harness routing where wire insulation may have rubbed against frame components or been damaged by heat exposure.

Step 2: Electrical Circuit Testing Using a digital multimeter, disconnect the sensor harness connector and measure resistance across sensor terminals (typically 3-wire sensor with signal, ground, and 5V reference). Consult Komatsu specifications, but expect approximately 1-5 kΩ depending on temperature. Check for 5V reference voltage from the ECM with key on, engine off. Inspect harness continuity between sensor connector and ECM pins, checking for values below 5Ω resistance and no shorts to ground.

Step 3: Pressure Line Verification and Sensor Replacement Remove both pressure sensing tubes and verify they are clear by blowing compressed air through them (maximum 30 PSI). Inspect tube fittings at DPF ports for carbon buildup that could restrict pressure signal transmission. If electrical and pressure lines test correctly, replace the differential pressure sensor with a genuine Komatsu part. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) and perform a stationary regeneration cycle to verify proper sensor operation.

Step 4: Post-Repair Validation Monitor live data through diagnostic software during engine operation, verifying the differential pressure sensor reads 0-2 inches H₂O at idle and increases appropriately under load. On used machines with unknown service history, consider inspecting the actual DPF condition, as excessive soot loading from deferred maintenance may have damaged the sensor or related components.

---

Disclaimer: This guide provides general troubleshooting information for Code CA155. Always consult the official Komatsu service manual for your specific machine serial number and seek assistance from certified Komatsu technicians for complex repairs involving emission control systems.