John Deere S660 Problems – Proven Fixes For Grain Loss And Engine

Operating a massive piece of machinery like the John Deere S660 during a busy harvest season is a high-stakes endeavor. You depend on this Class 6 combine to deliver clean grain and consistent throughput without failing in the middle of a field.

However, even the most reliable equipment can develop mechanical hiccups that slow your progress. When you start encountering john deere s660 problems, it can feel like your entire season is hanging in the balance.

In this guide, we will break down the most frequent mechanical failures and performance issues associated with this model. You will learn how to troubleshoot engine codes, optimize grain flow, and maintain your hydraulic systems like a professional technician.

Identifying Common john deere s660 problems and Mechanical Faults

The S660 is a workhorse, but its complex TriStream rotor and STS (Single-Tine System) technology require precise adjustment. If the settings are even slightly off, you will notice a significant drop in efficiency and grain quality.

One of the primary complaints involves the cleaning shoe performance, where grain exits the rear of the machine instead of the tank. This often points to an imbalance between the fan speed and the chaffer openings, requiring immediate recalibration.

Engine-related issues often center on the Tier 4 emission standards, which utilize complex exhaust after-treatment systems. Understanding how to manage these sensors and filters is the first step in avoiding the dreaded “limp mode” during operation.

Excessive Grain Loss and Shoe Performance

Grain loss is perhaps the most frustrating issue for any operator, as it represents direct profit falling onto the soil. In the S660, this is frequently caused by overloading the cleaning shoe because the rotor is not separating the material properly.

Check your concave clearance first; if it is too wide, the grain stays trapped in the straw. Conversely, if the clearance is too tight, you may end up with cracked grain and excessive tailings that plug the return system.

Adjust the fan speed in small increments of 50 RPM to find the sweet spot for your specific crop moisture. If the air is too weak, the chaff won’t float; if it is too strong, it will blow your harvest right out the back.

Feeder House and Header Drive Issues

The feeder house is the gateway for your crop, and any restriction here brings the entire machine to a halt. Operators often report slugging in heavy or green-stemmed crops, which puts immense strain on the drive belts.

Inspect the feeder house floor for wear or “washboarding,” which can catch material and cause bunching. Ensure the chain tension is within the manufacturer’s specification to prevent the chain from jumping the sprockets under heavy load.

The variable-speed header drive can also suffer from hydraulic leaks or solenoid failures. If the header speed fluctuates unexpectedly, check the electrical connections at the valve block for corrosion or loose wires.

Engine and Emission System Troubleshooting

The PowerTech engine in the S660 is designed for high torque, but it is sensitive to fuel quality and cooling efficiency. Many john deere s660 problems originate in the cooling package, which can quickly become clogged with dust and chaff.

A clogged radiator leads to elevated engine temperatures, which triggers the computer to de-rate the engine’s power. Blow out the cooling cores daily with compressed air, paying close attention to the air-to-air cooler and the AC condenser.

Modern diesel engines also rely on the DPF (Diesel Particulate Filter) to meet emission standards. If the machine does not reach high enough operating temperatures, the filter will clog, requiring a forced regeneration or a costly manual cleaning.

Fuel System Sensitivity

The high-pressure common rail fuel system requires ultra-low sulfur diesel and high-quality filtration. If you notice a loss of power or rough idling, your primary fuel filter is likely restricted by contaminants or microbial growth.

Change your fuel filters at the recommended intervals, and always keep a spare set in the cab. Draining the water separator daily is a simple habit that prevents injector damage and expensive fuel pump repairs down the road.

Check the fuel lines for any signs of air leaks, especially around the primer bulb and the filter housings. Even a tiny amount of air in the fuel system can cause the engine to stumble under heavy harvesting loads.

Managing the Exhaust After-Treatment

The Selective Catalytic Reduction (SCR) system requires Diesel Exhaust Fluid (DEF) to function. If the DEF quality is poor or the tank is contaminated with dirt, the sensors will trigger a fault code that limits your ground speed.

Store your DEF in a cool, shaded area to prevent it from degrading, as heat can break down the urea content. Always clean the area around the DEF fill cap before opening it to ensure no field dust enters the tank.

If you see a “Regen Required” light, do not ignore it; allow the machine to complete its cycle. Interrupting a regeneration cycle repeatedly can lead to a permanent soot buildup that requires a technician to resolve.

Hydraulic System and Electronic Sensor Glitches

The S660 relies heavily on hydraulics for everything from steering to the hydrostatic transmission. Overheating is the number one enemy of hydraulic health, often caused by low fluid levels or a failing oil cooler.

Electronic sensors, such as the moisture sensor and the mass flow sensor, are critical for precision farming data. If these sensors provide erratic readings, your yield maps will be inaccurate, making it harder to plan for next year’s fertilization.

Solving john deere s660 problems related to electronics usually begins with a thorough inspection of the wiring harness. Look for frayed wires where the harness rubs against the frame or where rodents may have chewed on the insulation during the off-season.

Calibrating the Yield Monitor

To get accurate data, you must calibrate the mass flow sensor at the beginning of each season and whenever you switch crops. This involves weighing several loads on a certified scale and entering the data into the GreenStar display.

If the moisture sensor is reading high, check the sensor plate for a buildup of “gum” or crop residue. Wiping the sensor with a clean cloth and ensuring the auger is moving material past it smoothly will usually fix the issue.

Check the elevator chain tension, as a loose chain can cause the grain to bounce, leading to inconsistent sensor readings. Proper tension ensures a steady flow of grain across the impact plate for the most accurate yield data.

Hydrostatic Drive Maintenance

The hydrostatic transmission provides the smooth, infinite speed control required for varying crop densities. If the machine feels sluggish or “whines” excessively, the hydrostatic oil may be breaking down or the filters may be bypassed.

Check the oil level in the reservoir when the machine is cold and on level ground. Use only the recommended John Deere Hy-Gard fluid, as generic hydraulic oils may not provide the necessary friction modifiers for the wet brakes and clutches.

Inspect the drive belts that power the hydro pump; a glazed or cracked belt will slip under load, reducing your climbing ability. Replacing a worn drive belt is a relatively simple task that prevents a major breakdown in the field.

Proactive Maintenance Schedule for Longevity

Preventative maintenance is the best way to ensure your S660 stays out of the shop and in the field. Creating a daily, weekly, and seasonal checklist will help you catch small issues before they turn into catastrophic failures.

Focus on the “grease points” identified in your operator’s manual, particularly the high-speed bearings on the rotor and the chopper. Use a high-temperature grease that can withstand the heat generated by hours of continuous operation.

Inspect the wear parts inside the combine, such as the rasp bars and the concave wires. If the leading edges of the rasp bars are rounded, they won’t thresh effectively, leading to increased fuel consumption and grain loss.

• Daily: Check engine oil, coolant, and hydraulic fluid levels. Blow out the cooling package.
• Weekly: Inspect all drive belts for tension and wear. Grease the primary countershaft.
• Monthly: Check the battery terminals for corrosion and ensure the fire extinguisher is charged.
• Pre-Season: Replace fuel and air filters. Calibrate all electronic sensors and the yield monitor.

Inspecting the Rotor and Concaves

The heart of the S660 is the TriStream rotor, which uses a tapered design to move material efficiently. Over time, the tines and rasp bars will wear down, especially if you harvest in sandy soils or abrasive crops.

Check the gap between the rotor and the concaves using a feeler gauge to ensure it is uniform from front to back. An uneven gap causes slugging on one side and poor threshing on the other, wasting energy and grain.

Look for bent or broken concave wires that can allow large pieces of cob or straw to enter the cleaning shoe. Replacing a single concave section is much cheaper than dealing with a plugged return system or a damaged fan.

Safety Protocols for Heavy Machinery Repair

Working on a machine as large as the S660 requires a safety-first mindset. Never attempt to clear a plug or adjust a belt while the engine is running or the separator is engaged.

Always engage the feeder house lift cylinder safety stop before working under the header. This mechanical lock prevents the header from falling if a hydraulic hose fails while you are underneath it.

Wear appropriate personal protective equipment (PPE), including safety glasses and heavy-duty gloves. The dust generated during harvest can be highly irritating to the lungs, so consider wearing a respirator when blowing out the machine.

Frequently Asked Questions (FAQ)

Why is my John Deere S660 losing so much grain over the back?

Grain loss is usually caused by an imbalance between the rotor speed and the cleaning shoe settings. Ensure your concave clearance is tight enough to thresh the grain and that your fan speed is high enough to lift the chaff without blowing out the seeds.

What causes the “Limp Mode” or engine de-rate on the S660?

This is typically a protective measure triggered by the ECU (Engine Control Unit). Common triggers include clogged DPF filters, low DEF levels, or high engine temperatures caused by a dirty radiator or cooling package.

How often should I change the hydraulic oil in my S660?

You should generally change the hydraulic oil every 1,000 to 1,500 hours, or as specified in your manual. However, you should check the fluid quality and filter indicators daily to catch contamination early.

Why does my feeder house keep plugging in green crops?

Plugging often occurs when the feeder house chain is too loose or the floor is worn. Green-stemmed crops are “sticky,” so ensure your drum height is adjusted correctly to pull the material into the machine consistently.

Conclusion

Successfully managing john deere s660 problems requires a combination of regular maintenance and a keen eye for mechanical detail. By focusing on the cleaning shoe settings, engine cooling, and hydraulic health, you can maximize your harvest efficiency and minimize downtime.

Remember that the S660 is a precision instrument; small adjustments often yield the biggest results in grain quality. Keep your sensors calibrated, your filters clean, and your safety locks engaged to ensure a productive and safe harvest season.

If you encounter a problem that seems beyond your DIY capabilities, do not hesitate to contact your local dealer for a diagnostic scan. Staying proactive today ensures that your John Deere S660 remains a reliable partner in the field for many years to come.

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Taylor Galla

Founder and Author at Gardenaider

Taylor Galla is an American website author, product spokesman, mechanical engineer, automotive enthusiast, and automotive modifier.

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