The signal from the NOx sensor has been proven to drift with time. A calibration procedure is available in Cat® Electronic Technician (ET). This procedure adjusts the slope of the sensor to account for this drift. Periodic calibration of the NOx sensor is required too ensure accurate readings and optimum engine performance.
Perform regular air/fuel ratio adjustments and calibration adjustments for the NOx sensor according to the maintenance interval schedule for your engine. The sensor must be calibrated if the sensor value that is reported by Cat ET has a deviation that is reported to be within ±10 Part Per Million (PPM) of the value that is measured by an emissions analyzer. If the measured deviation of the sensor value is within ±10 PPM, calibration of the sensor is not necessary. Refer to Operation and Maintenance Manual, "Nitrogen Oxide Sensor - Calibrate" for interval recommendations.
During the calibration, the concentration of NOx that is reported by Cat ET is compared to the actual concentration that is reported while the exhaust is analyzed by an emissions analyzer. Cat ET allows the user to make incremental adjustments to the sensors slope value. The calibration procedure corrects the drift that is encountered over the life of the sensor. This calibration factor is stored in the Electronic Control Module (ECM) until a reset is requested or the sensor is recalibrated.
Note: Make small changes to the slope value during the calibration procedure. If large changes are made to the slope value, the engine operation may become unstable. Allow the engine to stabilize after each adjustment is made.
Note: A 391-8170 EMISSIONS ANALYZER TOOL GP - (Bluetooth Module) or a 393-0673 EMISSIONS ANALYZER TOOL GP can be used during the calibration procedure.
Before a calibration of the NOx sensor is performed, obtain a gas analysis of the fuel in order to confirm the settings of the engines fuel quality and gas-specific gravity. For information that is related to performing these adjustments, refer to Systems Operation/Testing and Adjusting, "Fuel System".
Calibration must be done during controlled engine operating conditions. The engine must be running and the operating conditions of the engine must be stabilized. Ensure that the requirements that are displayed on Cat ET are satisfied prior to initiating the calibration. If these conditions are not maintained during the entire calibration procedure, the calibration will be aborted.
Procedure for the Installation of a New NOx Sensor
If you are installing a new NOx sensor, the correction factor for the slope of the old sensor that is stored in the ECM must be reset. The new sensor must then be calibrated after the installation is complete.
Perform the following procedure to reset the correction factor for the NOx sensor:
- Stop the engine.
- Connect Cat ET to the service tool connector. Establish communications with the ECM.
- Access the "Service/Service Procedures/Engine Exhaust NOx Level Sensor Installation" screen of Cat ET. Use this screen in Cat ET to reset the correction factor. The new slope value is reset to 100 percent.
- Follow the prompts to guide you through the procedure.
- Cat ET will prompt you when the procedure is complete.
- Install the new sensor on the engine. Use Cat ET to calibrate the new sensor. Proceed to "Procedure for Calibration of the NOx Sensor"tocalibrate the new sensor.
Procedure for Calibration of the NOx Sensor
Perform the following procedure to calibrate the NOx sensor:
- Start the engine. Before continuing, allow the engine to warm to normal operating temperature.
- Connect a 391-8170 EMISSIONS ANALYZER TOOL GP - (Bluetooth Module) or a 393-0673 EMISSIONS ANALYZER TOOL GP to the engines exhaust system. Allow the NOx readings from the analyzer to stabilize.
- Connect Cat ET to the service tool connector. Establish communications with the ECM.
- Access the "Service/Calibrations/Engine Exhaust NOx Level Sensor Calibration" screen of Cat ET. Use Cat ET to start the calibration.
- Follow the prompts to guide you through the calibration procedure. Be sure to allow the engine to stabilize before each measurement is taken.
- Compare the value of the NOx that is reported from Cat ET to the value of NOx that is reported from the exhaust analyzer. Select the arrow buttons at the bottom of the calibration screen to increase or decrease the sensors slope value that is reported by Cat ET.
Note: Make small changes to the slope value during the calibration procedure. If large changes are made to the slope value, the engine operation may become unstable. Allow the engine to stabilize after each adjustment is made.
When the values are comparable within 10 PPM, click the "Next" button at the bottom of the screen.
- Cat ET will prompt you to allow the engine to stabilize for three minutes to verify the correct settings.
- If necessary, perform the calibration procedure again to recalibrate the sensor.