Decoding your John Deere fault codes is a safeguard to prevent downtime and protect your investment. And it’s not difficult as long as you know the right way.
This guide is your go-to resource. We’ll break down the structure of John Deere Diagnostic Trouble Codes (DTCs), provide a list of the most common fault codes, and give you a clear action plan.
What Is the SPN and FMI?
First things first: John Deere fault codes aren’t random. They follow a standardized system (SAE J1939) that’s surprisingly logical once you know the secret. A complete code is made of three parts:
Controller Address: This tells you which computer on the machine is reporting the problem. Think of it as the department raising the alarm. Common ones include:
- ECU: Engine Control Unit (The brain of your engine)
- VCU: Vehicle Control Unit
- HCU: Hydraulic Control Unit
- TCU: Transmission Control Unit
- BCU: Basic Control Unit
- PDU: Primary Display Unit (Your dashboard display)
SPN (Suspect Parameter Number): This is a standardized number that identifies the specific component or system with the issue. For example, SPN 110 will always refer to Engine Coolant Temperature, no matter the machine.
FMI (Failure Mode Identifier): This number describes the type of failure. The FMI tells you exactly whether the voltage is too high, the data is erratic, or the pressure to low.
Let’s put it together with an example:
You see the code: ECU SPN 100.FMI 1
- ECU: The Engine Control Unit is talking.
- SPN 100: The issue is with the Engine Oil Pressure.
- FMI 1: The failure mode is “Data Valid but Below Normal Operational Range.”
Translation: Your engine oil pressure is dangerously low. Stop the engine immediately.
See? Not so scary when you can speak the language.
John Deere Fault Codes Sheet
While a complete John Deere fault codes list PDF for every model is impractical (they are constantly updated and model-specific), a huge number of codes are universal. The following codes chart covers the most critical and frequent faults you’ll encounter on everything from a John Deere 333G skid steer to a large tractor.
Engine System
| Fault Code (SPN.FMI) | Description & Action Required |
|---|---|
| SPN 100.FMI 1 | Low Engine Oil Pressure – CRITICAL STOP! Immediately shut down the engine to prevent severe damage. Check oil level. Do not restart until the cause is found. |
| SPN 110.FMI 0 | High Engine Coolant Temperature – CRITICAL STOP! The engine is overheating. Shut down safely. Check coolant level (once cool), look for debris blocking the radiator, and check fan belt tension. |
| SPN 111.FMI 1 | Low Engine Coolant Level – WARNING. Top off coolant and inspect for leaks in hoses, the radiator, and the water pump. |
| SPN 94.FMI 1 | Low Fuel Supply Pressure – WARNING. The engine may lose power or fail to start. The #1 cause is a clogged fuel filter. Start there. |
| SPN 157.FMI 1 | Low Fuel Rail Pressure – WARNING. It could be a high-pressure pump issue, injector leak, or sensor problem. Requires professional diagnosis. |
| SPN 520244.FMI 14 | DPF Soot Load High (Tier 4 Engines) – ACTION NEEDED. This is a common John Deere 333 G DEF system fault. The Diesel Particulate Filter needs to perform a “regeneration” cycle to burn off soot. If auto-regen fails, you must initiate a parked/manual regen. Ignoring this will lead to engine de-rating and a service call. |
Transmission/Drivetrain
| SPN 190.FMI 0 | High Engine Speed – WARNING. You are over-revving the engine, likely while going downhill in too high a gear. Downshift to use engine braking. |
|---|---|
| SPN 123.FMI 1 | Low Clutch Pressure – WARNING. Transmission may slip or fail to engage. Check the transmission fluid level and filter first. |
| SPN 70.FMI 31 | Park Brake Engaged While Moving – INFO/WARNING. The park brake switch is either on or the sensor is faulty—a critical safety interlock. |
Hydraulic System
| SPN 1638.FMI 0 | High Hydraulic Oil Temperature – WARNING. Continued operation can damage seals and pumps. Check the hydraulic oil level and ensure the hydraulic cooler is clean and free of debris. |
|---|
Electrical & CAN Bus
| SPN 168.FMI 1 | Low System Voltage – WARNING. The battery is not charging correctly. Check battery terminals for corrosion and tightness. Test the alternator output. |
|---|---|
| SPN 639.FMI 9 | CAN Bus Communication Error – WARNING. This is a very common John Deere ECU fault code. It means one of the controllers has lost communication with the others. A damaged wire, a faulty terminating resistor, or a failed controller can cause it. It can be tricky to diagnose. |
From Code to Action: How to Fix the Fault Codes
Seeing a code is one thing; knowing what to do is another. Here’s your game plan.
1. Access and Record the Code: Use your machine’s monitor (e.g., CommandCenter) to navigate to the diagnostics menu. Don’t just look at the code, write it down! Get the Controller, the SPN, and the FMI. Note whether it’s “Active” or “Stored.” Active codes are happening now; stored codes happened in the past.
2. Perform the “Operator 5-Minute Check”: Based on the code, do a quick visual inspection.
- Oil/Coolant/Hydraulic Code? Check the fluid levels and look for obvious leaks.
- Temperature Code? Check for debris blocking radiators and coolers.
- Electrical Code? Check battery connections and look for any visibly damaged wires or harnesses.
- Filter Code? When was the last time you changed your fuel/air/hydraulic filters?
3. Know When to Call for Backup: You are a skilled operator, not necessarily a certified technician. Do not start tearing into complex wiring or high-pressure fuel systems unless you have the training and tools. Call your dealer or a trusted mechanic if you encounter:
- Any CRITICAL STOP code that isn’t resolved by a simple fluid check.
- Persistent CAN Bus communication errors (e.g., SPN 639. FMI 9).
- Internal transmission or engine codes (e.g., low rail pressure, clutch pressure).
- Any fault requiring special diagnostic tools like John Deere Service ADVISOR™.
Final Words
Whether you’re searching for codes for a specific excavator, tractor, or skid steer, remember that your Operator’s Manual is your most valuable tool, containing diagnostics tailored to your exact machine.
Once you’ve used your diagnostic tool and manual to identify the problem—be it a faulty sensor, a worn belt, or a clogged filter—the next step is sourcing a reliable replacement. This is where we can help. For durable, high-quality components to complete your repair, explore our comprehensive John Deere Parts category. We have the parts you need to get your equipment back in the field, fast.
By understanding these codes and having a trusted source for parts, you become a more effective owner. You’ll catch problems early, reduce downtime, and keep your valuable green equipment running strong.
