Yanmar 4TN107 Fault Code P167C (SPN 3609 FMI 10): Complete Diagnostic Guide

What is Yanmar 4TN107 Fault Code P167C?

Fault Code P167C (SPN 3609 FMI 10) indicates an abnormal update rate or data transmission failure from the aftertreatment diesel exhaust fluid (DEF) dosing unit to the engine control module (ECM). This code is specific to Yanmar's emissions control system and signals that the DEF injector or its control circuit is not communicating properly with the ECM.

SPN 3609 refers to the aftertreatment fuel enable actuator, while FMI 10 designates an abnormal update rate — meaning the ECM is receiving data too slowly, intermittently, or not at all. In the Yanmar 4TN107 engine, this directly impacts the selective catalytic reduction (SCR) system's ability to control NOx emissions. If left unresolved, this fault can trigger engine derate or prevent the machine from meeting emission compliance, especially critical in used excavators operating under strict environmental regulations.

Common Symptoms

When fault code P167C is active, operators typically experience:

• Yellow or amber engine warning light illuminated on the instrument cluster
• Engine power derate after a grace period (typically 1-4 hours of operation)
• DEF system malfunction indicator displayed on the monitor
• Intermittent loss of communication between the DEF doser and ECM, visible in diagnostic software
• No visible exhaust smoke, but potential for increased NOx emissions during testing

Potential Causes

The most common technical causes for P167C on used Yanmar 4TN107 engines include:

• Corroded or damaged wiring harness at the DEF dosing unit connector — particularly common in machines exposed to road salt or coastal environments
• Failed DEF injector solenoid due to crystallized DEF buildup or internal electrical failure
• Loose or corroded ground connection on the aftertreatment system harness
• ECM software version incompatibility or corrupted calibration files (especially in machines with aftermarket ECM replacements)
• Intermittent open circuit caused by harness rubbing against frame rails or hydraulic lines near the exhaust system
• Water intrusion into the DEF doser connector from improper sealing or damaged connector boot

How to Troubleshoot and Fix Code P167C

Step 1: Visual Inspection

Begin by inspecting the DEF dosing unit located on the exhaust system. Check the electrical connector for corrosion, bent pins, or DEF crystal buildup. On used excavators, pay special attention to the wiring harness routing — look for signs of abrasion where the harness crosses metal brackets or comes near heat sources. Verify the connector boot is intact and properly sealed.

Step 2: Electrical Testing

Using a digital multimeter, check the DEF injector circuit. With the ignition off, disconnect the DEF doser connector and measure resistance across the solenoid terminals (typically 3-8 ohms for Yanmar units). Next, verify supply voltage at the connector with ignition on — you should see approximately 12V on the power supply pin. Check ground circuit continuity to ensure less than 0.5 ohms resistance to chassis ground.

Step 3: Communication Verification

Connect Yanmar diagnostic software (or compatible J1939 scan tool) to read live data from the DEF system. Monitor the DEF injector command signal versus actual response rate. An abnormal update rate will show delayed response times or missing data frames. Clear the fault code and perform a DEF injector activation test through the diagnostic software to confirm real-time communication.

Step 4: Component Replacement (If Needed)

If electrical tests pass but communication fails, the DEF dosing unit itself is likely faulty. Before replacement, flush the DEF supply lines to remove any crystallized urea. When installing a new doser on used equipment, always replace the connector pigtail and apply dielectric grease to prevent future corrosion. After installation, perform an ECM relearn procedure to synchronize the new component.

Step 5: Preventive Measures for Used Machines

For older Yanmar 4TN107 engines, inspect harness tie-downs and ensure proper clearance from moving parts. Apply protective loom to exposed wiring near the turbocharger and exhaust components. Verify DEF quality and system winterization to prevent crystallization-related failures.

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Disclaimer: This guide provides general diagnostic procedures for fault code P167C. Emission system repairs may require certified technicians and specialized equipment. Always consult the official Yanmar service manual and comply with local emission regulations. Improper repairs can result in engine damage, emission violations, or safety hazards.