John Deere 2931.02 – CCU (Chassis Control Unit): Foot Brake Oil Level Switch Voltage Issue, Check Brake Circuit.

SPN 2931 is the standard J1939 parameter for the "Hydraulic Brake Fluid Level Switch". FMI 02 indicates that the data is erratic, intermittent, or incorrect (a voltage issue). The controller is detecting an abnormal voltage signal from the brake fluid level switch circuit, which typically means there is an open circuit, a short circuit, a damaged sensor, or a wiring harness issue preventing the controller from accurately reading the brake fluid level.

• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 5050E
• 5058E
• 5067E
• 5075E
• 5075M
• 5115ML
• 9120
• 9220
• 9320
• 9420
• 9520
• CSX7080
• CTS Combine Harvesters

1. 1

   Physically check the hydraulic brake fluid reservoir to see if the fluid is critically low

2. 2

   Inspect the wiring harness leading from the brake fluid level switch to the CCU for chafed wires, pinched harnesses, or melted insulation

3. 3

   Disconnect the brake fluid level switch connector and check for water intrusion, corrosion, or pushed-out pins

4. 4

   Check for continuity on the ground circuit of the switch using a multimeter

5. 5

   Check the signal wire for a short to ground or short to power

6. 6

   Measure the resistance of the switch itself by manually moving the float (if accessible) or testing it while full vs. empty to verify it opens and closes properly

1. 1

   Secure the Machine

   Park the machine on a level surface, engage the parking brake, turn off the engine, and remove the key.

2. 2

   Top Off Fluid (If Applicable)

   If the reservoir is simply low, fill it with the OEM-specified brake/hydraulic fluid to the "MAX" line.

3. 3

   Repair Wiring (If Applicable)

   If the multimeter test revealed high resistance (greater than 5 ohms on the ground circuit) or a short in the signal wire, trace the harness back to the CCU and splice/repair the damaged section using weather-sealed connectors.

4. 4

   Replace the Switch

   If the switch fails the continuity test (e.g., it reads open when the float is down, or shorted when the float is up): Clean the area around the brake fluid reservoir to prevent dirt from entering the hydraulic system. Disconnect the electrical connector from the switch. Depending on the model, either unthread the switch from the reservoir or replace the reservoir cap assembly (as the switch is often integrated into the cap/float assembly). Install the new switch/cap and reconnect the wiring harness.

5. 5

   Clear Codes

   Turn the key to the ON position and use a John Deere Service ADVISOR tool (or the onboard diagnostic dash menu) to clear the CCU 002931.02 fault code.

6. 6

   Test Operation

   Depress the foot brake several times to ensure normal operation and verify the code does not return.