John Deere 168.04 – Gear Shift Module Direct Drive (GPM): Voltage Below Normal / Shorted to Low Source

The unswitched supply voltage to the module has dropped below normal operating parameters (typically below 9.0 volts). This is usually caused by a depleted battery, inadequate charging from the alternator, or poor electrical connections in the wiring harness.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R

1. 1

   Inspect the battery to verify it is providing sufficient voltage (12V+ when off, ~14V when running) and check for degradation.

2. 2

   Evaluate the charging system by testing the alternator and voltage regulator under load.

3. 3

   Visually inspect wiring and connectors around the batteries, alternator, and the unswitched power supply to the GPM for damage or loose connections.

4. 4

   Measure the supply voltage directly at the GPM input harness using a multimeter to ensure it is above 9.0 volts.

5. 5

   Inspect the power supply fuses related to the transmission and cab control units.

1. 1

   Attempt Vehicle Recovery

   Reduce the electrical load in the cab (turn off lights, A/C, etc.) or increase engine RPM to see if the alternator can recover the voltage drop.

2. 2

   Cycle Power

   Power down the tractor, check the relevant fuses, and cycle the key switch to see if the code clears.

3. 3

   Clean Connections

   If voltage is low at the battery, clean and secure all battery terminals and chassis ground connections to ensure proper electrical contact.

4. 4

   Repair Wiring

   If the battery and alternator test fine but voltage at the GPM is low, trace the unswitched power wire back to the battery/fuse panel and repair any shorts, chafed wires, or corroded pins.

5. 5

   Replace Faulty Charging Components

   If the alternator fails testing, replace the alternator and/or batteries.

6. 6

   Reset System

   After resolving the voltage drop, restart the tractor and test the transmission shifting to ensure proper functionality is restored and the code remains inactive.