Massey Ferguson 521010.03 – Engine ECU (EEM4): DEF Tank Heater Coolant Valve Solenoid Low Side Short Circuit to HIGH SOURCE

The system has detected that the low side (ground/return circuit) of the DEF tank heater's coolant control solenoid valve is short-circuited to a high voltage source (e.g., +12V or +24V). This prevents the valve from operating correctly, which can lead to the DEF fluid freezing in cold temperatures or overheating if the valve is stuck open.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 7600 Series
• Dyna-4
• Dyna-6

1. 1

   Inspect the wiring harness running from the Engine ECU to the DEF tank heater coolant valve for chafed insulation, melted wires, or pinch points where the low-side wire might be shorting to a power wire.

2. 2

   Disconnect the plug at the DEF coolant valve and the Engine ECU. Check for water intrusion, corrosion, or bent pins that could bridge the circuits.

3. 3

   With the key ON (engine off) and the valve disconnected, probe the low-side (ground) pin on the harness connector. If it shows +12V (or +24V), there is a short to power in the wiring harness that must be traced and repaired.

4. 4

   Measure the resistance across the pins of the DEF tank heater coolant valve solenoid itself. If it is internally shorted, the valve must be replaced.

1. 1

   Safely Prep the Machine

   Turn off the ignition, remove the key, and disconnect the negative battery terminal.

2. 2

   Locate the Valve

   Locate the DEF tank heater coolant control valve, which is typically spliced into the engine coolant lines routing toward the DEF tank.

3. 3

   Isolate the Coolant Lines

   Clamp off the coolant hoses on both sides of the valve to prevent excessive coolant loss, or drain the coolant system below the level of the valve.

4. 4

   Remove the Faulty Valve

   Disconnect the electrical connector. Loosen the hose clamps, detach the coolant lines from the valve, and unbolt the valve from its mounting bracket.

5. 5

   Install the New Valve

   Mount the replacement valve, reattach the coolant hoses, and secure the hose clamps.

6. 6

   Reconnect

   Plug the electrical connector back into the solenoid.

7. 7

   Refill and Bleed

   Unclamp the hoses, top off the engine coolant as necessary, and bleed any air from the cooling system.

8. 8

   Clear Codes

   Reconnect the battery. Use an AGCO EDT (Electronic Diagnostic Tool) or equivalent scanner to clear the inactive fault codes. Run the engine and verify that there are no coolant leaks and the code does not return.