Circuit DescriptionThe ambient air temperature sensor is a variable resistor sensor and is used to measure the temperature of the ambient air. The engine control module (ECM) uses this temperature reading to optimize engine performance, and determine if heating of the SCR system is required. The engine control module (ECM) supplies 5 volts to the ambient air temperature signal circuit. The ECM monitors the change in voltage caused by changes in the resistance of the sensor to determine the ambient air temperature. Component LocationThe mounting location for the ambient air temperature sensor is OEM dependent. Refer to the appropriate OEM...

Circuit DescriptionThe vehicle speed sensor senses the speed of the tailshaft gear on the vehicle’s transmission. This speed signal is then transmitted to the engine control module (ECM) and converted into a vehicle speed. Component LocationThe vehicle speed sensor is located in the rear of the vehicle transmission. Refer to the OEM service manual for location. Conditions for Running the DiagnosticsThis diagnostic runs continuously when the vehicle is in motion, if the feature is enabled.Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected a loss of vehicle speed when other engine operating conditions indicated that the vehicle should...

Circuit DescriptionThe Engine Control Module (ECM) calculates a calibration memory checksum based on the values of certain parameters in the ECM. This checksum is compared to an expected value in the ECM to detect tampering. Component LocationThe ECM mounting location varies, depending on the engine model, and may be mounted either on or off the engine. Conditions for Running the DiagnosticsThis diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running. Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected the calibration memory checksum did not match the expected value or...

Circuit DescriptionThe vehicle speed sensor senses the speed of the tailshaft gear on the vehicle’s transmission. This speed signal is then transmitted to the engine control module (ECM) and converted into a vehicle speed. Component LocationThe vehicle speed sensor is located in the rear of the vehicle transmission. Refer to the OEM service manual for location. Conditions for Running the DiagnosticsThe adjustable parameter “VSS Anti-Tampering” must be enabled.This diagnostic runs continuously when the vehicle is in motion, if the feature is enabled.Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected a tampering event of the vehicle speed signal....

Circuit DescriptionThe coolant level sensor is a switch and is used to measure the level of the engine coolant in the radiator top tank. The coolant level sensor is immersed in the coolant and returns a different signal voltage when immersed in coolant versus being out of coolant. The engine control module (ECM) monitors the change in the signal voltage to determine the level of the engine coolant. Component LocationThe engine coolant level sensor is typically located in the radiator top tank or surge tank. Refer to the OEM service manual for the location. Conditions for Running the DiagnosticsThis diagnostic...