Komatsu PC850-8R Fault Code S-13: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code S-13?

Fault Code S-13 on the Komatsu PC850-8R indicates a malfunction in the engine speed sensor circuit or an abnormal signal from the crankshaft position sensor. This code is triggered when the Electronic Control Module (ECM) detects an irregular or missing signal from the sensor that monitors engine rotational speed and crankshaft position.

The engine speed sensor is critical for the PC850-8R's performance because it provides real-time data to the ECM for fuel injection timing, engine speed control, and overall power management. Without accurate readings, the machine cannot optimize combustion efficiency or maintain proper hydraulic system performance. In used excavators, this sensor circuit is particularly vulnerable to wear from vibration, heat exposure, and connector corrosion common in high-hour machines.

Common Symptoms

When Code S-13 is active on your PC850-8R, operators typically experience:

• Engine cranks but fails to start or experiences extended cranking time before ignition
• Intermittent engine stalling during operation, especially under load or at idle
• Loss of engine power or inability to reach rated RPM
• Monitor panel warning light illuminated with fault code display
• Erratic engine speed fluctuations or rough running conditions

Potential Causes

The most common technical reasons for S-13 appearing on used PC850-8R excavators include:

• Failed or degraded engine speed sensor due to heat stress or internal component failure
• Damaged sensor wiring harness from rubbing against engine components or frame rails (common wear point near the flywheel housing)
• Corroded or loose electrical connectors at the sensor or ECM interface
• Broken or damaged reluctor ring teeth on the crankshaft or flywheel
• ECM internal fault or corrupted sensor signal processing (less common)
• Inadequate sensor air gap caused by mounting bracket wear or improper installation

How to Troubleshoot and Fix Code S-13

Step 1: Visual Inspection Begin by locating the engine speed sensor (typically mounted near the flywheel housing on the PC850-8R). Inspect the sensor body for physical damage, oil contamination, or mounting looseness. Check the wiring harness from sensor to ECM for chafing, cuts, or heat damage—pay special attention to routing near hot exhaust components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. Komatsu specifications typically call for 500-1500 ohms (verify with your service manual). Check for voltage supply at the connector (usually 5V or 12V reference from ECM). Inspect connector pins for corrosion, bent terminals, or moisture intrusion—common issues in used machines.

Step 3: Signal and Air Gap Verification With a Komatsu diagnostic software tool (KOMTRAX or compatible scanner), monitor live sensor signal while cranking. The signal should show consistent pulses. Physically verify the air gap between sensor tip and reluctor ring (typically 0.5-1.5mm). On high-hour excavators, check the reluctor ring for missing teeth or debris buildup.

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu parts to ensure proper ECM communication. After installation, clear codes using diagnostic software and perform a test run under load. For used excavators, always apply dielectric grease to connectors to prevent future corrosion.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC850-8R service manual and consider professional technician assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.