John Deere 158.04 – CCU: Switched Supply Voltage Low

The control module has detected that its switched power supply has dropped below the acceptable operating threshold (typically below 9.0 volts). This low voltage condition can cause the module to disable certain functions to prevent erratic operation or system damage.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 7200R
• 7215R
• 7230R
• 7260R
• 7280R
• 8225R
• 8245R
• 8270R
• 8295R
• 8320R
• 8335R
• 8345R
• 8370R
• 8400R
• 7020
• 7030
• 9020
• 9030
• 9RT

1. 1

   Attempt Vehicle Recovery: Reduce the electrical load (turn off cab lights, HVAC, etc.) and increase the engine RPM to see if the alternator can boost the voltage enough to clear the code.

2. 2

   Power Cycle: Turn the key switch off, wait a few moments, and restart the tractor. Sometimes the code is a temporary communication glitch that clears upon a reboot.

3. 3

   Visual Inspection: Visually inspect around the batteries and alternator for any signs of physical damage, loose cables, or accumulated debris that could cause a short or poor ground.

4. 4

   Fuse Check: Power down the machine and check the system fuses (specifically the power supply fuses routing to the CCU/Rear Chassis Module).

5. 5

   Voltage Drop Test: Use a multimeter to verify the actual voltage at the CCU harness connector. If the connector shows 12V+ but the CCU reports under 9V, the module itself may be failing.

1. 1

   Clean and Tighten Battery Terminals

   Remove the battery cables, clean the posts and terminals of any corrosion, and securely tighten them. Poor battery connections are the leading cause of 158.04 low voltage codes.

2. 2

   Test the Charging System

   With the engine running, test the alternator output at the battery. It should read between 13.5V and 14.5V. If it reads near or below 12V, replace the alternator and/or drive belt.

3. 3

   Inspect the CCU Wiring Harness

   Locate the Chassis Control Unit. Disconnect the main harness and inspect the pins for moisture, corrosion, or pushed-out terminals. Clean with electrical contact cleaner and apply dielectric grease before reconnecting.

4. 4

   Trace the Switched Power Circuit

   If the battery and alternator are fine, trace the switched power wire from the ignition/fuse panel to the CCU. Look for chafed insulation or pinched wires along the chassis frame. Repair any damaged wiring.

5. 5

   Replace the CCU

   If the wiring, battery, and alternator are all in perfect working order and the CCU connector is receiving proper voltage, the CCU has an internal fault. Replace the module. (Note: A new CCU will require programming/calibration by a John Deere dealer using Service ADVISOR™ software).