SENSOR-NITROGEN OXIDE 4615585 - Caterpillar

Probable Causes
The gas supply to the engine is insufficient.
A feature for engine protection prevents the engine from starting.
The starting motor circuit is faulty.
There is no engine speed signal to the Electronic Control Module (ECM).
The ignition system is not functioning.
The base timing is incorrect.Recommended Repairs
Check the Gas Supply to the Engine
Check for low gas pressure. Observe the angle of the throttle plate while you crank the engine.If the gas pressure is low, refer to Troubleshooting, "Fuel Pressure".If the throttle does not open, troubleshoot the electrohydraulic oil system. The gas supply lines may require purging before servicing.Check for Active Shutdowns
Use the Caterpillar Electronic Technician (ET) to check for active diagnostic codes or for event codes which may prevent the engine from starting.Correct the cause of the active code. Before the engine can be started, you must recycle the power to the engine. Set the engine control to the OFF/RESET mode. Then set the control to the STOP mode.Check the Status of the Relay for the Starting Motor
Attempt to start the engine while you observe the status of the relay for the starting motor on Cat ET.If the status of the relay for the starting motor indicates that the engine should crank but no cranking occurs, troubleshoot the starting circuit. Refer to Systems Operation/Testing and Adjusting, "Air/Electric Starting System".If the engine should crank and cranking occurs, check the engine rpm.Check the Engine Speed
The ECM must detect a minimum of 50 rpm before the gas and the ignition are supplied to the engine. Use Cat ET to monitor the engine speed while you crank the engine.If no engine speed is displayed on Cat ET or if the engine speed is not stable, troubleshoot the speed/timing sensor. Refer to Troubleshooting, "Engine Speed/Timing Sensor".Check for Diagnostic Codes
Check for active diagnostic codes that relate to the ignition system. If there is at least one active diagnostic code that relates to the ignition system, troubleshoot the diagnostic code.Check the Base Timing
Verify that the base timing is correct. Refer to Systems Operation/Testing and Adjusting, "Ignition Timing - Adjust".