New Holland ENG 3674 – Engine Control Unit (ECU): EGR Under Voltage Error for H-bridge

The voltage supplied to the H-bridge circuit inside the Engine Control Unit (ECU) has dropped below the operational threshold, preventing the ECU from properly actuating the EGR valve.

• L213
• L216
• L220
• SR175
• TR340
• B90B
• B100B
• T5.110
• T5.120

1. 1

   Check system voltage by testing the battery voltage and alternator output for high voltage fluctuations or overall low system voltage

2. 2

   Inspect the main wiring harness connecting the Engine ECU to the EGR valve, specifically checking the 60-pin connector at the engine for chafed wires, corrosion, or loose pins

3. 3

   Verify that the main power supply and ground circuits to the Engine ECU are clean, tight, and providing full battery voltage under load

1. 1

   Resolve Electrical Issues

   Repair any underlying electrical system issues found during the diagnostic checks (e.g., failing alternator, bad batteries, or damaged wiring).

2. 2

   Replace the Engine ECU

   If the vehicle's electrical system is providing stable and correct voltage but the code persists, the H-bridge circuit inside the ECU has likely suffered internal damage due to voltage fluctuations. The Engine ECU must be replaced.

3. 3

   Reprogramming

   If the Engine ECU (EDC) is replaced, you must use the appropriate New Holland Electronic Service Tool (EST) to reload the engine dataset and restore the self-learning parameters.