John Deere 1321.05 – Engine Control Unit (ECU): Engine Starter Solenoid Lockout Relay Circuit Has High Resistance

The Engine Control Unit (ECU) has detected abnormally high electrical resistance in the engine starter solenoid lockout relay circuit (also known as the neutral start relay). This is typically caused by an open circuit or poor electrical connections, resulting in insufficient current reaching the starter relay. When this fault is active, the ECU may limit or disable the starter solenoid, leading to a no-start condition and triggering a yellow caution light.

• 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
• 370E
• 410E
• 460E
• 770G
• 770GP
• 772G
• 772GP
• 318D
• 320D
• 210L EP
• 210LJ
• 540G-III
• 548G-III
• PowerTech 3029
• PowerTech 4.5L
• PowerTech 6.8L
• PowerTech 9.0L

1. 1

   Check for intermittent faults to determine if the DTC periodically goes away, which indicates a loose connection rather than a hard failure.

2. 2

   Visually inspect the starter solenoid lockout relay (neutral start relay) and its wiring harness for signs of physical damage, corrosion, or loose terminal connections.

3. 3

   Turn the key switch to the ON/START position and listen for an audible 'click' from the relay to verify activation.

4. 4

   Use a digital multimeter to measure the resistance in the relay circuit, tracing the wiring from the ECU to the relay to identify the exact point of high resistance or open break.

1. 1

   Disconnect Power

   Always disconnect the battery or turn off the master disconnect switch before performing electrical repairs.

2. 2

   Repair Wiring/Connectors

   If the multimeter test revealed an open circuit or high resistance in the harness, repair or replace the damaged wires, connectors, or ground terminals to restore proper circuit continuity.

3. 3

   Replace the Relay

   If the wiring is intact but the relay failed the activation test (or shows internal high resistance), remove the defective starter solenoid lockout relay and install a new OEM replacement.

4. 4

   Clear Codes and Test

   Reconnect the battery. Reset the ECU to clear the 001321.05 error code. Cycle the key and test the starter system to confirm the engine cranks and the code does not return.