John Deere 111.01 – Engine Control Unit (ECU): Engine Coolant Level Extremely Low

The sensor in the coolant surge tank/header tank has detected that the fluid has dropped below the minimum safe operating threshold. As a protective measure, the system will typically limit engine power (derate), disable power boost, and in severe cases, command an engine shutdown to prevent catastrophic overheating damage.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5M series
• 5E series
• 6M series
• 6R series
• 7R series
• 8R series
• 8RT series
• 8RX series
• 9R/9RT series
• 130G
• 160G
• 210G
• 250G
• 300G
• CTS
• WTS
• 7000-series self-propelled forage harvesters
• 9000-series combines
• 7760 Cotton Pickers
• articulated dump trucks
• wheel loaders
• forestry equipment (skidders, forwarders)

1. 1

   Verify Physical Coolant Level: Check the actual coolant level in the surge tank/radiator. Do not rely solely on the sensor reading.

2. 2

   Cold Leak Inspection: If the tank is low, inspect the entire cooling system for leaks. Pay special attention to radiator hose clamps, heater hoses, the water pump seal, and the head gasket. Leaks are often most visible during a "cold start" first thing in the morning.

3. 3

   Inspect the Sensor: If the coolant level is completely full but the code is active, the sensor is likely the culprit. The sensor sits at the bottom of the header tank and is highly prone to corrosion over time due to heat cycles and coolant additives.

4. 4

   Check Wiring & Connectors: Inspect the wiring harness leading to the coolant level switch for shorts to ground, frayed wires, or open circuits.

1. 1

   Top Off Fluids

   If the coolant is genuinely low, fill the reservoir to the appropriate level using an approved OEM coolant (e.g., John Deere COOL-GARD II).

2. 2

   Repair Leaks

   Tighten any loose hose clamps or replace leaking hoses/seals discovered during the diagnostic phase.

3. 3

   Clear the Code

   Cycle the ignition key or use a diagnostic tool to clear the ECU code. Run the machine to see if the code returns.

4. 4

   Replace the Sensor (If necessary)

   If the code immediately returns despite a full tank and good wiring, the sensor has failed internally. Drain the coolant reservoir below the level of the sensor port. Disconnect the electrical harness from the sensor. Unthread/remove the old sensor from the header tank. Install the new sensor, reconnect the harness, and refill the coolant.