John Deere 168.18 – PTQ: Supply Voltage (BAT) Too Low

The control unit has detected that the system voltage has fallen below an acceptable operating threshold (usually below 9 volts, or below 11.2V–12.5V while the engine is running above 500–1500 RPM). The module may restrict or disable functions such as shifting to protect the system from erratic operations and preserve battery life.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 7210R
• 7230R
• 7250R
• 7185J
• 7195J
• 7205J
• 7720
• 7820
• 7920
• 7630
• 7730
• 7830
• 7930

1. 1

   Test the batteries separately for resting voltage (should be ~12.6V) and perform a load test to ensure they are not deeply discharged or suffering from dead cells.

2. 2

   Inspect all battery terminals, chassis grounds, and the alternator B+ cable for corrosion, looseness, or damage.

3. 3

   Start the engine and measure the voltage at the battery. The alternator should maintain a system voltage between 13.5V and 14.5V. If it drops below 11.2V at idle or 12.5V at high RPM, the charging system is failing.

4. 4

   Check the specific power supply fuses to the PTQ / Rear Chassis Module (e.g., F5 or F9, depending on the tractor model) for partial blows or poor contact.

5. 5

   Measure the voltage directly at the PTQ module connector. If the battery shows 12V+ but the module connector shows <9V, there is a high-resistance short or open circuit in the wiring harness.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable(s) to ensure safety.

2. 2

   Clean Connections

   Use a wire brush and battery cleaner to thoroughly clean the battery posts and cable terminals. Reconnect and tighten them to OEM torque specifications.

3. 3

   Replace Batteries

   If the batteries failed the load test, replace them. Always replace batteries in pairs on 24V systems or parallel 12V systems.

4. 4

   Replace Alternator

   If the alternator failed the charging system test, relieve the serpentine belt tension, disconnect the electrical connections, unbolt the alternator, and install a replacement. Verify belt condition and tension upon reassembly.

5. 5

   Repair Wiring/Fuses

   Replace any blown fuses supplying the PTQ. If voltage drop was found in the harness, trace the wire from the fuse panel to the Rear Chassis Module and repair any chafed, corroded, or broken sections.

6. 6

   Clear Codes and Test

   Reconnect all power, start the tractor, and use a diagnostic tool (or the onboard display) to clear the PTQ 000168.18 code. Run the engine above 1500 RPM and verify the code does not return and that transmission shifting functions normally.