Cummins ISB4.5 CM2150 Fault Code: 2556 PID: SPN: 729 FMI: 4 Engine Intake Air Heater 1 Circuit – Voltage Below Normal or Shorted to Low Source.

Circuit Description
The intake air heater improves starting and white smoke control in cold ambient conditions.

The engine control module (ECM) controls relays that switch power to the intake air heater. Air heaters on 12 volt systems will have two relays and 24 volt systems only require one relay.

Component Location
The intake air heater is located at the air inlet connection to the intake manifold. The location of the intake air heater relays will vary by vehicle and engine configuration.

Conditions for Running the Diagnostics
This diagnostic runs when the keyswitch is in the ON position and when the pulse width modulated (PWM) device is activated. In some cases, the diagnostic can also run at certain fixed intervals.

Conditions for Setting the Fault Codes
The intake air heater circuit pulse width modulated (PWM) signal is not detected to be system voltage when the pulse width modulated (PWM) signal is turned on.

Action Taken When the Fault Code is Active
-The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
-The intake air heater circuit will be disabled.

Conditions for Clearing the Fault Code
-To validate the repair, start the engine and let it idle for 1 minute.
-The ECM will turn off the amber CHECK ENGINE light and the fault code will go inactive immediately after the diagnostic runs and passes.
-This fault code can also be cleared with INSITE™ electronic service tool.

Possible Causes
-A shorted intake air heater relay
-Intake air heater relay supply wire shorted to ground.