Massey Ferguson E4357.03 – Engine Control Unit (ECU) / AGCO SISU POWER EEM4: DEF Injector Supply Pipe Heater Resistance Is High (ECU) / DEF pressure line heater relay low side (line relay) open circuit

The engine management system has detected an open circuit or abnormally high resistance on the low side (ground/control side) of the DEF pressure line heater relay circuit.

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

1. 1

   Inspect the DEF pressure line heater relay socket for corrosion, pushed-out pins, or moisture

2. 2

   Use a multimeter to check the continuity of the low-side control wire running from the Engine ECU to the DEF pressure line heater relay for an open circuit

3. 3

   Swap the DEF pressure line heater relay with a known good relay of the same type (e.g., a work light relay) to see if the fault changes or clears

4. 4

   Disconnect the DEF injector supply pipe electrical connector and measure the resistance across the heater element pins to check if the element has failed (infinite/open resistance)

1. 1

   Power Down

   Turn the ignition off and wait a minimum of 60 seconds for the ECU to fully power down and save data.

2. 2

   Access the Relay Panel

   Locate the emissions/DEF relay block.

3. 3

   Test/Replace the Relay

   If the relay swap test (from the diagnostic steps) resolved the issue, replace the faulty DEF pressure line heater relay.

4. 4

   Repair Wiring

   If the relay is good but the low-side control wire has no continuity to the ECU, trace the wiring harness back to the ECU. Repair any broken wires or corroded connectors.

5. 5

   Replace the DEF Supply Pipe

   If the relay and wiring are intact but the heater element inside the DEF supply pipe is burnt out (high resistance), the entire DEF Injector Supply Pipe must be replaced, as the heater is integrated into the line.

6. 6

   System Reset

   After repairs are made, turn the ignition off for at least 60 seconds, then back on. Clear the inactive fault codes using a diagnostic service tool.