Cummins ISB4.5 CM2150 Fault Code: 357 PID: 132 SPN: 132 FMI: 4 Engine Intake Air Mass Flow Circuit – Voltage Below Normal or Shorted to Low Source.

Circuit Description
The mass air flow sensor is a frequency based device. A constant voltage is applied to a heated wire. This wire is positioned in the air stream and is heated by the electrical current that the voltage produces. As air flows across it, it cools down. The heated wire or film is a positive temperature coefficient (ptc) resistor. This means that the resistance drops when the temperature drops. The drop in resistance allows more current to flow through it in order to maintain the programmed temperature. This current is changed to a frequency which is sent to the ECM and interpreted as air flow. Adjustments for air temperature and humidity are taken into consideration since they also affect the temperature of the heated wire or film. The mass air flow sensor receives a 12 volt power supply from the ECM.

Component Location
The mass air flow sensor is located in the air box of the intake system.

Conditions for Running the Diagnostics
This diagnosic consists of two parts, an engine off and an engine running portion. The engine off portion runs only at initial key ON. The engine running portion runs when the EGR valve is commanded closed, and compares an estimated charge air flow value to the mass air flow sensor reading.

Conditions for Setting the Fault Codes
This diagnostic sets if the mass air flow sensor reports a value lower than what is allowable for the sensor at key ON, or when the engine is running with the EGR valve closed.

Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE lamp and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.

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 lamp immediately after the diagnostic runs and passes.
-The ECM will turn off the MIL after three consecutive ignition cycles that the diagnostic runs and passes.
-This fault code and MIL can also be cleared with INSITE™ electronic service tool.

Shop Talk
The mass air flow sensor can not be cleaned or serviced, and must be replaced if contaminated or damaged.

Possible Causes
-Mass air flow sensor malfunction
-ECM malfunction
-Sensor supply circuit open or shorted to ground in harness or sensor
-Signal circuit open or shorted to ground in harness or sensor
-Intermittent fault condition