John Deere 1321.06 – ECU: Engine Starter Solenoid Lockout Relay Circuit Has Low Resistance

This code triggers when the control module detects abnormally low resistance (or a short circuit to ground) in the drive circuit of the starter solenoid lockout relay, which can prevent the starter solenoid from engaging properly and result in limited or no engine starting function.

• 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
• 318D
• 320D
• 770G
• 770GP
• 772G
• 772GP
• 315SK
• 210LJ Landscape Loader
• 540G-III
• 548G-III
• 540H
• 548H Skidders
• 870G Excavator
• 7210R
• 7230R
• 7250R

1. 1

   Determine if the DTC is intermittent, which indicates a loose connection or a wire occasionally rubbing against the chassis.

2. 2

   Visually inspect the starter relay (often designated as K5, K12, or K20) and its wiring harness for signs of damage, melted insulation, corrosion, or loose connections.

3. 3

   Use a multimeter to measure the resistance in the relay circuit, checking for continuity to ground on the control side of the relay to pinpoint any short circuit.

4. 4

   Verify if the relay clicks or activates when the ECU sends the start signal (key turned to START with the machine in neutral) to test for internal shorting.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery via the battery disconnect switch to prevent electrical arcing during repair.

2. 2

   Access the Relay Panel

   Locate the starter/neutral start relay in the machine's main fuse/relay panel or firewall (refer to the specific machine's schematic for exact location).

3. 3

   Repair or Replace Faulty Wiring

   If the multimeter test revealed a short to ground in the wiring harness, trace the wire from the ECU to the relay. Repair or replace any damaged wires, connectors, or terminals to restore proper circuit isolation.

4. 4

   Replace Faulty Relay

   If the wiring is intact but the relay itself has an internal short (causing the low resistance reading), remove the old relay and install a new OEM replacement.

5. 5

   Reassemble and Reconnect

   Secure the wiring harness and reconnect the battery power.

6. 6

   Reset ECU and Verify Operation

   Turn the key switch ON, clear the stored ECU fault codes, and attempt to start the engine. Verify that the starter engages normally and that the 001321.06 code does not return.