Grid Heater Bypass   Installing this bypass will allow you to manually control if and for how long you want to run the grid heaters when the ECM is commanding the grid heaters on.  This will reduce the load on the alternator/charging system and in turn reduce the harmful AC voltage.  This bypass will also keep the fault codes P0380 Intake Air Heater Relay #1 Control Circuit and P0382 Intake Air Heater Relay #2 Control Circuit from being set.        Parts