ELECTRONIC CONTROL SYSTEM Inlet Air Heater Relay • The Inlet Air Heater (IAH) element is used to improve cold start operation, reduce emissions and white smoke, and improve engine warm-up. The relay is mounted next to the Power Distribution Center and is the taller of the two relays. The IAH relay receives battery power from the starter power-feed terminal and the normally open terminal connects to the element through the harness. One end of the relay coil is grounded through the engine 12-way connector. The relay closes when the coil receives voltage from the ECM. AIR HEATER RELAY AIR HEATER RELAY Glow Plug Relay • Glow plugs are used to improve cold engine starting.
Glow plug operation is controlled by the ECM through the glow plug relay. The glow plug relay is mounted next to the Power Distribution Center and is the shorter of the two relays. The relay common terminal is connected by jumper to the common terminal of the Inlet Air Heater relay. The normally open terminal connects to the glow plug harness. One end of the relay coil is grounded through the engine 12-way connector. The relay is closed when the other end of the coil receives voltage from the ECM. GLOW PLUG RELAY GLOW PLUG RELAY Injection Pressure Regulator (IPR) Valve • The IPR mounts to the high-pressure pump and controls the amount of oil allowed to drain from the high-pressure system.
When the ECM increases the IPR signal duty cycle, the valve blocks the oil’s path to drain and pressure rises. When the ECM reduces the duty cycle, a larger volume of oil is allowed to drain from the system and pressure is reduced. The valve contains a pressure relief valve for the system that opens if system pressure reaches 4500 psi. The IPR is protected by a heat shield that must be reinstalled after servicing. SWIVEL CONNECTOR SWIVEL CONNECTOR IPR IPR International ® VT 275 V6 Engine 25