Cummins ISX11.9 CM2250 (2010-12) Fault Code: 2556 PID: SID 70 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 electronic control module (ECM) controls relays that switch power to the intake air heater. Air heaters on 12 volt systems will have two relays while 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 PWM signal is not detected to be system voltage when the 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 fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.
For on-board diagnostic (OBD) engines, the ECM will turn off the malfunction indicator lamp (MIL) after three consecutive trips where the diagnostic runs and passes.
The Reset All Faults command in INSITE? electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications

Shop Talk
Possible causes of this fault code include:

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

Possible Cause:
1) OEM harness
2) ECM failure