John Deere 168.16 – ECU: High Battery Voltage At Engine Module (ECU)

The control unit detects that the unswitched supply voltage (BAT) has exceeded 16 volts (typically registering between 16V and 18V). This condition indicates a potential overcharging scenario within the vehicle's electrical system.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6120 to 6420
• 6120L to 6520L
• 9470RT
• 9520RT
• 9570RT
• 444J
• 544J
• 624J
• 7400A TerrainCut

1. 1

   Test Battery and Charging System Voltage: Using a multimeter, measure the voltage at the battery terminals while the engine is off, and again while the engine is running. Normal running voltage should be around 13.5V to 14.5V. If it exceeds 16V, the system is overcharging.

2. 2

   Inspect the Alternator and Voltage Regulator: Check the alternator wiring and connections for shorts or corrosion. The voltage regulator (which is internally mounted on most modern John Deere alternators) is the most likely culprit for failing to cap the voltage output.

3. 3

   Check Battery Condition: Inspect the battery and battery cables. A severely damaged battery with internal shorts can sometimes cause the alternator to overwork and spike voltage.

1. 1

   Disconnect Power

   Turn off the engine and disconnect the negative battery cable to prevent electrical shock or further damage to the ECU.

2. 2

   Replace the Faulty Component

   If the diagnostic tests confirm that the alternator is outputting more than 16V, the internal voltage regulator has failed. Because the regulator is typically integrated, you will need to replace the entire alternator assembly.

3. 3

   Reassemble and Reconnect

   Install the new alternator, tension the drive belt to OEM specifications, and reconnect the battery cables.

4. 4

   Reset ECU and Verify Operation

   Start the engine and measure the voltage at the battery again to ensure it is now regulating properly (below 15V). Clear the fault codes from the ECU/BCU using a John Deere diagnostic tool or OBD-II scanner, and verify that 000168.16 does not return.