DISC A. 3D9876 - Caterpillar

Probable Causes
Incorrect air/fuel ratio
Intake manifold air temperature sensor
Intake manifold pressure sensorRecommended Actions
Incorrect Air/Fuel Ratio
An air/fuel mixture that is too lean will have an adverse effect on engine operation. Verify that the exhaust emissions are correct. Confirm that the sensor calibration for the NOX sensor is correct. Refer to Troubleshooting, "Nitrogen Oxide Sensor - Calibrate".A change in the fuel energy content will change the air/fuel ratio. Obtain a fuel analysis for the fuel supply.The fuel supply pressure must be adequate and stable. Ensure that the fuel pressure is within specifications.Intake Manifold Air Temperature Sensor
An intake manifold air temperature sensor that is producing an incorrect signal will have an adverse effect on the air/fuel ratio. Verify that the sensor is producing the correct signal. Measure the temperature of the intake manifold air with a thermometer. Compare the reading with the value that is displayed on the Caterpillar Electronic Technician (ET). Replace the sensor, if necessary.Note: Be sure to use an accurate thermometer for your measurements. Use of gauges that are not properly calibrated can lead to an improper diagnosis of the problem.Intake Manifold Pressure Sensor
An intake manifold pressure sensor that is producing an incorrect signal will have an adverse effect on the air/fuel ratio. Verify that the sensor is producing the correct signal. Measure the intake manifold pressure with a gauge. Compare the reading with the value that is displayed on Cat ET. Replace the sensor, if necessary.Note: Be sure to use an accurate gauge for your measurements. Use of gauges that are not properly calibrated can lead to an improper diagnosis of the problem.