What is Komatsu PC210-7 Fault Code E306?

Fault Code E306 on the Komatsu PC210-7 excavator indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically a CAN (Controller Area Network) bus communication error between the engine controller and the monitor panel. This code signals that the ECM is unable to properly transmit or receive data packets across the CAN network, which is the digital communication backbone that allows various electronic control units to share critical operational data.

This fault is particularly critical for the PC210-7 because it can prevent the operator from receiving accurate engine parameters, hydraulic system temperatures, and diagnostic information on the monitor display. When CAN bus communication fails, the machine may enter a protective derate mode or display incomplete operational data, compromising both productivity and safety on the jobsite.

Common Symptoms

When Code E306 is active on your Komatsu PC210-7, you may experience:

• Monitor panel displays intermittent or no engine data (RPM, fuel level, coolant temperature readings become erratic or freeze)
• Warning lights flash simultaneously or illuminate without corresponding actual faults
• Engine may enter limp mode or refuse to start despite cranking normally
• Diagnostic functions become unavailable through the standard monitor interface
• Intermittent loss of throttle response or unexpected engine speed variations during operation

Potential Causes

The most common technical causes for E306 on used PC210-7 excavators include:

• CAN bus wiring harness damage at known rub points near the engine mount brackets and behind the operator cab (vibration wear is common on machines with 5,000+ hours)
• Corroded or loose connector pins at the ECM C1 connector or the monitor panel connector, especially on machines operated in coastal or high-moisture environments
• Failed terminating resistor within the CAN network (typically located at network endpoints)
• ECM internal circuit failure due to voltage spikes from alternator irregularities or jump-starting procedures
• Aftermarket component interference such as improperly installed telematics systems or non-OEM monitor replacements
• Damaged shielding on CAN wiring allowing electromagnetic interference from starter motor or hydraulic solenoids

How to Troubleshoot and Fix Code E306

Step 1: Visual Inspection of CAN Bus Harness Begin by physically inspecting the CAN-H and CAN-L wiring (typically twisted-pair yellow and green wires) from the ECM to the monitor panel. On used PC210-7s, check the harness routing behind the battery box and along the right-side frame rail where contact with hydraulic lines commonly causes abrasion. Look for exposed copper, melted insulation, or previous repair attempts with electrical tape.

Step 2: Connector Pin Integrity Check Disconnect the ECM connector C1 and the monitor panel connector. Inspect all pins for corrosion, bent contacts, or moisture intrusion. Use electrical contact cleaner and a small wire brush on corroded pins. Check for proper pin tension—connectors on older machines often have weakened spring tension causing intermittent contact. Measure continuity between ECM pins and monitor panel using a digital multimeter (should read less than 5 ohms resistance).

Step 3: CAN Bus Voltage Testing With the key in the ON position (engine off), use a multimeter to measure voltage between CAN-H and CAN-L terminals at the ECM connector. You should read approximately 2.5V on each line relative to ground when the network is idle. The differential voltage between CAN-H and CAN-L should fluctuate between 1-3V during communication. Readings outside this range indicate a short to ground, open circuit, or terminating resistor failure.

Step 4: Terminating Resistor Verification The PC210-7 CAN network requires 120-ohm terminating resistors at both network ends. With the key OFF and all controllers disconnected, measure resistance between CAN-H and CAN-L—you should read approximately 60 ohms (two 120-ohm resistors in parallel). If you read infinite resistance, a terminating resistor has failed or been accidentally removed during previous repairs.

Step 5: Use Komatsu KOMTRAX or Diagnostic Software For comprehensive diagnosis, connect Komatsu diagnostic software (KTEC)—aftermarket tools like Jaltest or Nexiq with Komatsu coverage also work. Check for additional stored codes that may indicate which specific controller has dropped off the network. Monitor live CAN bus traffic to identify which node is not responding.

Critical Note for Used Excavators: Before replacing the expensive ECM (often $2,000+ for genuine Komatsu units), thoroughly check all wiring and connectors. Approximately 80% of E306 faults on higher-hour machines stem from harness wear and connector corrosion rather than controller failure. Pay special attention to areas where harnesses pass through metal grommets or contact moving components.

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Disclaimer: This guide provides general diagnostic procedures for Code E306. Always consult the official Komatsu PC210-7 service manual for model-specific specifications and torque values. If you're uncomfortable performing electrical diagnostics, or if the fault persists after addressing wiring issues, consult a certified Komatsu technician or qualified heavy equipment diesel mechanic. Improper electrical work can cause additional ECM damage or create safety hazards.