John Deere 520956.05 – Engine Control Unit (ECU): Battery Cutoff Relay Drive Circuit Has High Resistance

The control module is detecting that the electrical resistance in the circuit responsible for triggering the battery cutoff relay is higher than the acceptable threshold, leading to low amperage.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6090MC
• 6090RC
• 6100MC
• 6100RC
• 6110MC
• 6110RC

1. 1

   Inspect the battery cutoff relay, its socket, and the surrounding fuse panel for signs of corrosion, moisture intrusion, or burnt/loose pins.

2. 2

   Measure the resistance of the drive circuit wiring between the Engine ECU and the battery cutoff relay socket using a multimeter. Look for chafed wires, pinched harnesses, or degraded grounds.

3. 3

   Remove the battery cutoff relay and bench test it for internal resistance and proper switching operation when 12V is applied.

4. 4

   Check the main battery connections and chassis grounds with a voltage drop test to ensure the low amps reading isn't a symptom of a broader voltage supply issue.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable to ensure safety while working on the electrical system.

2. 2

   Access the Relay

   Locate the battery cutoff relay in the machine's main fuse/relay distribution box.

3. 3

   Clean Contacts

   If corrosion is found in the relay socket, use electrical contact cleaner and a terminal brush to clean the pins.

4. 4

   Repair Wiring

   If the multimeter test showed high resistance in the harness, splice and repair the damaged section of the wire, or replace the damaged connector terminal.

5. 5

   Replace the Relay

   If the wiring is sound but the relay failed the bench test (or if the internal coil has degraded), install a new battery cutoff relay.

6. 6

   Reassemble and Clear Codes

   Reconnect the battery, turn on the ignition, and use a John Deere Service ADVISOR tool (or compatible scanner) to clear the 520956.05 fault code.

7. 7

   Verify Repair

   Cycle the key and start the tractor to ensure the code does not return and the battery cutoff system engages/disengages properly.