What is Yanmar General Fault Code P1340?

Fault Code P1340 indicates a malfunction in the Camshaft Position Sensor (CMP) "A" Circuit, specifically pointing to a correlation or timing issue between the crankshaft and camshaft position sensors. This diagnostic trouble code (DTC) triggers when the Engine Control Module (ECM) detects an inconsistency in the expected timing relationship between these two critical sensors, which are essential for proper fuel injection timing and ignition sequencing in Yanmar diesel engines.

In Yanmar excavators, this code is particularly critical because precise camshaft-to-crankshaft synchronization directly affects combustion efficiency, fuel delivery, and overall engine performance. When the ECM cannot verify proper valve timing correlation, it may enter a protective mode to prevent potential engine damage. For used excavators, this fault often stems from sensor degradation, timing component wear, or electrical connection deterioration over thousands of operating hours.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the instrument panel
• Hard starting or extended cranking time, especially during cold starts
• Rough idle, engine misfiring, or noticeable loss of power during operation
• Engine may enter derate mode (reduced power output) to protect internal components
• Increased fuel consumption and excessive black or white exhaust smoke

Potential Causes

The most frequent causes of P1340 in used Yanmar excavators include:

• Camshaft Position Sensor failure due to heat exposure, oil contamination, or internal component breakdown
• Crankshaft Position Sensor malfunction or inconsistent signal output
• Worn or stretched timing chain/belt causing actual mechanical timing deviation between camshaft and crankshaft
• Damaged or corroded wiring harness connections at sensor plugs—common rub points include areas near the engine block and valve cover
• ECM software corruption or internal processor issues (less common but possible in older units)
• Low engine oil level or contaminated oil affecting Variable Valve Timing (VVT) solenoid operation (if equipped)
• Damaged reluctor ring or tone wheel on camshaft or crankshaft assemblies

How to Troubleshoot and Fix Code P1340

Step 1: Visual Inspection and Connection Check Begin by inspecting both the Camshaft Position Sensor and Crankshaft Position Sensor wiring harnesses for visible damage, chafing, or corrosion. On used excavators, pay special attention to connector pins for green corrosion or bent terminals. Clean all connections with electrical contact cleaner and ensure proper seating.

Step 2: Sensor Testing with Multimeter Using a digital multimeter, test sensor resistance values. Typical Yanmar CMP sensors should read between 500-1500 ohms (consult your specific service manual). Check for voltage supply at the sensor connector—you should see approximately 5 volts reference voltage from the ECM with the key on, engine off.

Step 3: Mechanical Timing Verification If sensors test within specifications, perform a mechanical timing inspection. Remove the timing cover and check timing chain/belt tension and condition. Look for excessive slack, worn guides, or damaged teeth. Verify timing marks align correctly at Top Dead Center (TDC).

Step 4: Advanced Diagnostics Connect Yanmar-compatible diagnostic software to view live sensor data. Compare crankshaft and camshaft position signals during cranking—they should maintain consistent correlation. If signals are erratic or out of phase, replace the faulty sensor. For persistent codes after sensor replacement, inspect the reluctor wheel for damage or missing teeth.

Step 5: ECM Considerations If all mechanical and electrical components test properly, the ECM may require reprogramming or replacement. This is more common in excavators with 8,000+ operating hours.

---

Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult your Yanmar service manual and consider professional diagnostic assistance for complex electrical or mechanical repairs. Improper repairs may cause additional damage or safety hazards.