What is Komatsu PC60-7 Fault Code S-11?

Fault Code S-11 on the Komatsu PC60-7 excavator indicates a malfunction in the engine preheating system, specifically related to the glow plug relay circuit or intake air heater system. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage signal, open circuit, or excessive resistance in the preheating circuit that prepares the diesel engine for cold starts.

For the PC60-7's 4D95LE engine, proper preheating is critical for reliable cold-weather starting and preventing excessive white smoke during initial operation. When this system fails, the combustion chamber temperature remains insufficient for optimal fuel atomization, leading to hard starts and increased engine wear during warm-up cycles.

Common Symptoms

When Code S-11 is active, operators typically experience:

• Difficult or prolonged cranking during cold starts, especially in temperatures below 40°F (4°C)
• Excessive white or gray smoke emitting from the exhaust for the first 2-5 minutes of operation
• Glow plug indicator light remaining illuminated longer than normal or flashing intermittently
• Rough idle immediately after cold starts with noticeable engine shaking
• Extended warm-up period required before hydraulic functions operate smoothly

Potential Causes

The most common technical reasons for S-11 fault activation include:

• Failed glow plug relay due to contact point corrosion or coil burnout (extremely common on machines with 5,000+ hours)
• Damaged wiring harness near the engine firewall where cables rub against the frame during operation
• Individual glow plug failure creating circuit imbalance (one or more of the four plugs showing excessive resistance)
• Corroded electrical connectors at the relay mounting point or ECM interface, typical in used machines exposed to moisture
• ECM voltage irregularities caused by poor ground connections at the battery negative terminal or chassis ground points
• Intake air heater element breakage (if equipped with grid heater instead of standard glow plugs)

How to Troubleshoot and Fix Code S-11

Step 1: Visual Inspection and Connector Check Begin by inspecting the glow plug relay located near the fuel injection pump. Check for visible corrosion, burnt contacts, or heat damage. On used excavators, examine the wiring harness running along the left side of the engine block for abrasion marks where it contacts metal surfaces—this is a known wear point on PC60-7 models with over 4,000 operating hours.

Step 2: Electrical Testing Using a digital multimeter, check battery voltage (should read 12.4-12.8V with engine off). Test the relay coil resistance between terminals 85 and 86 (should read 70-90 ohms). With the key in the preheat position, verify the relay receives 12V signal from the ECM. Check each glow plug resistance individually by disconnecting the bus bar—each plug should measure 0.5-2.0 ohms. Readings above 6 ohms indicate a failed glow plug.

Step 3: Circuit Continuity and Repair Trace the circuit from the ECM connector (Pin C-23) to the relay and then to each glow plug. Look specifically for green wire corrosion at the firewall grommet—a common failure point. Clean all ground connections with a wire brush and apply dielectric grease. If individual glow plugs are faulty, replace the complete set rather than singles to ensure uniform heating. After repairs, clear the code using Komatsu diagnostic software or by disconnecting the battery negative terminal for 30 seconds.

Disclaimer: This guide provides general troubleshooting information. Always consult the Komatsu PC60-7 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional system damage or safety hazards.