John Deere 3353.31 – Engine Control Unit (ECU): Alternator Fault / Alternator without function / No Alternator Condition Exists / Alternator Excitation Condition Exists

The control module has detected that the alternator output voltage has been low for greater than 10 seconds, or there is an open/bad connection in the smart regulator signal circuit. This means the alternator is not charging the electrical system or providing the expected excitation signal.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5E Series
• 5M Series
• 5065M
• 5075M
• 5085E
• 5085M
• 5090E
• 5100E
• 5115ML
• 8R/RW Series
• 8235R
• 8400R
• 700K
• 750K
• 850K
• 950K
• 1050K
• 670G
• 770G
• 772G
• 870G
• 250D
• 300D
• 310SK
• 410K
• 7400A TerrainCut
• 7760 Cotton Picker

1. 1

   Check if the DTC periodically goes away, which indicates an intermittent wiring connection rather than a failed alternator.

2. 2

   Inspect the engine for a broken, loose, or slipping alternator drive belt.

3. 3

   Inspect the wiring harness and connections at the alternator smart regulator and the ECU for an open circuit, short circuit, or bad connection.

4. 4

   Verify the actual voltage output at the vehicle controller or battery using a multimeter while the engine is running to confirm the low voltage condition.

1. 1

   Safety First

   Turn off the engine, remove the key, and disconnect the negative battery cable before servicing the electrical system.

2. 2

   Belt Replacement/Tensioning

   If the diagnostic check revealed a broken or loose serpentine/drive belt, replace the belt or adjust the tensioner.

3. 3

   Harness Repair

   If wiring damage or a loose connector was found during the visual inspection, clean the contacts, repair the broken wire, or replace the pigtail connector.

4. 4

   Alternator Replacement

   If the belt and wiring are intact but the alternator fails to output proper voltage (or fails bench testing), remove the drive belt, disconnect the B+ and regulator electrical connections, remove the mounting bolts, and extract the faulty alternator. Install the new alternator, torque mounting bolts to spec, and reattach the wiring.

5. 5

   Reassembly and Clearing Codes

   Reinstall the drive belt, reconnect the battery, start the engine, and verify that the charging system is operating at the correct voltage (typically ~14V for 12V systems or ~28V for 24V systems). Clear the 003353.31 fault code via the monitor or diagnostic tool.