Case IH 3668 – Engine Controller (Engine ECU / EDC): EGR Valve Circuit - Over temperature error for H-bridge

Over temperature error for H-bridge. The H-bridge is the internal driver circuit within the engine controller that operates the Exhaust Gas Recirculation (EGR) valve motor. When the EGR valve sticks, binds, or has a short circuit, it draws excessive electrical current, causing the H-bridge driver inside the ECU to overheat.

• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• Backhoe Loaders (580N, 590SN)
• Tractors (Farmall, Maxxum)

1. 1

   Clear the code and operate the machine to see if the H-bridge over-temperature was a momentary glitch

2. 2

   Remove and inspect the EGR valve for mechanical binding or heavy carbon fouling

3. 3

   Inspect the wiring harness between the Engine Controller and the EGR valve for chafing, shorts to ground, or shorts to battery

4. 4

   Test the resistance of the EGR valve motor to ensure it is within OEM specifications and not internally shorted

1. 1

   Clear the Fault

   Use the Electronic Service Tool (EST) to clear the code. Run the engine to operating temperature to see if the code returns.

2. 2

   Address EGR Valve/Wiring

   If the code returns, and your diagnostics point to a stuck valve or damaged wiring, clean/replace the EGR valve or repair the wiring harness.

3. 3

   Replace Engine Controller

   If the wiring is perfectly intact and the EGR valve is functioning normally (or has been replaced), but the 3668 fault code persists, the H-bridge driver inside the ECU is permanently damaged. You must replace the Engine Controller.

4. 4

   Restore Self-Learning Parameters

   Whether you replace the EGR valve or the Engine Controller, you must connect the Case IH Electronic Service Tool (EST) and run the procedure to 'Restore Self Learning Parameters' (also referred to in the manuals as 'Reset ECU data - EGR valve') so the ECU can learn the end-stops of the valve.