John Deere 158.03 – Air Conditioning Module (ETC): Switched Supply Voltage High

The control module is receiving an ignition supply voltage that exceeds the maximum safe operating threshold (typically >16.0 volts), which can cause erratic behavior or damage to the module's internal components.

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

1. 1

   Check the charging system (overcharging cause): Use a multimeter to measure the voltage at the battery terminals while the engine is running above 1500 RPM. If the voltage is reading above 16 volts, the alternator is overcharging.

2. 2

   Visually inspect the alternator and batteries for physical damage, loose connections, or accumulated debris.

3. 3

   Inspect the alternator output cable and battery cables for corrosion or short circuits.

4. 4

   Check the wiring harness (isolated module cause): If the alternator output is normal (approx. 13.5V - 14.5V) but the ETC module still logs the code, check the wiring harness leading to the Air Conditioning Module for a short to a higher voltage source.

1. 1

   Power Down

   Turn off the engine and visually inspect the battery and alternator wiring. Clean any debris around the battery and alternator terminals.

2. 2

   Test Alternator Output

   Start the vehicle and test the alternator output voltage.

3. 3

   Address Overcharging

   If the voltage is confirmed to be over 16 volts, the alternator's internal voltage regulator has failed. You must replace the alternator (or the voltage regulator, if serviced separately on your specific model).

4. 4

   Address Wiring/Module (If Alternator is Good)

   If the charging system is outputting normal voltage, trace the switched ignition supply wire to the ETC module. Repair any shorts in the harness. If the wiring is intact, the ETC module itself may have an internal fault and require replacement.

5. 5

   Clear Codes

   Cycle the key switch to see if the code clears. If the code persists after repairs, use a John Deere diagnostic scan tool to clear the stored DTCs.

6. 6

   Verify Repair

   Restart the engine and operate the tractor to ensure the voltage remains stable and the code does not return.