John Deere 520956.06 – ECU (Engine Control Unit) or Monitor Controller (DSZ): Battery Cutoff Relay Drive Circuit Has Low Resistance

A high-current or short-circuit condition in the battery disconnect system, where the control module detects that the circuit responsible for driving the battery cut-off relay (or its associated indicator LED) is drawing excessive amperage, usually due to a short to ground or an internally shorted relay coil.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 8245R
• 8270R
• 8295R
• 8320R
• 8335R
• 8345R
• 8370R
• 8400R
• 9470RT
• 9520RT
• 9570RT
• 6090MC
• 6090RC
• 6100MC
• 6100RC
• 6110MC
• 6110RC
• 130G

1. 1

   Visually inspect the wiring harness running from the ECU (or DSZ monitor) to the battery disconnect relay and the disconnect indicator LED for chafed wires, melted insulation, or pinched harnesses.

2. 2

   Disconnect the battery cutoff relay and measure the resistance of the drive circuit. If resistance is lower than OEM specification, trace the wire back to the ECU to locate the short.

3. 3

   Test the battery disconnect relay by measuring the resistance across the relay coil pins. A reading near 0 ohms indicates an internal short.

4. 4

   If equipped, check the battery disconnect LED indicator and its wiring for a short to ground.

1. 1

   Power Down

   Turn off the machine and manually disconnect the main negative battery cable to ensure safety while working on high-amperage electrical components.

2. 2

   Access the Relay

   Locate the automatic battery disconnect relay (usually located near the main battery box or main electrical distribution center).

3. 3

   Harness Repair (If Applicable)

   If the diagnostic checks revealed a short to ground in the wiring harness or LED indicator circuit, repair the damaged wire using heat-shrink butt connectors or replace the affected harness section.

4. 4

   Replace the Relay

   If the wiring is intact but the relay coil is shorted, remove the retaining hardware and disconnect the high-current cables and the low-voltage control plug. Install the new battery disconnect relay.

5. 5

   Reassemble and Reconnect

   Reattach all cables to the new relay, ensuring high-current terminals are torqued to specification to prevent arcing. Reconnect the main negative battery cable.

6. 6

   Clear Codes

   Turn the key to the ON position, use a John Deere Service ADVISOR tool (or onboard diagnostic monitor) to clear the 520956.06 historical code, and cycle the battery disconnect switch to verify proper operation without the code returning.