2500 4x4 Pickup L6-359 5.9L DSL Turbo (1995)
Air Intake Heater Relay: Description and Operation
Air Intake Heater Relay Operation
Intake Manifold Air Heater Relays
OPERATION
The Powertrain Control Module (PCM) operates the intake manifold air heater through the intake manifold air heater relays. The relays may be
energized before and after cranking, depending upon intake manifold air temperature. The PCM monitors intake manifold air temperature through
the intake manifold air temperature sensor.
The relays are not energized during engine cranking. When they are energized they make a clicking noise.
CAUTION: When testing, do not energize the air heater relays more than once per 15 minutes without running and operating the engine. Due to
the high amperage needed to operate the heater, the batteries may not have enough time to recharge. Wait 15 minutes before turning the key back
to the ON position.
CIRCUIT OPERATION
When the ignition switch is in the START or RUN position, it connects circuit A1 from fuse 3 in the PDC to circuit A21. Circuit A21 powers
circuit Fl8 through fuse 9 in the fuse block. Circuit F18 supplies battery voltage to the coil side of each intake manifold air heater relay
The Powertrain Control Module (PCM) provides ground for the coil in each relay on separate circuits. The PCM grounds first relay on circuit
S21; it grounds the second relay on circuit S22.
When the first intake manifold air heater relay energizes, its contacts close and connect circuit A19 from the left battery positive terminal to circuit
A58. Circuit A58 connects to the intake air heater.
When the second intake manifold air heater relay energizes, its contacts close and connect circuit A8 from the left battery positive terminal to
circuit A122. Circuit A122 connects to the intake air heater
