Circuit DescriptionThe water-in-fuel sensor is attached to the fuel filter. The engine control module (ECM) provides a 5 volt reference signal to the water-in-fuel sensor. When the water collected in the fuel filter covers the sensor probes, the water-in-fuel sensor pulls the 5-VDC reference voltage to ground, indicating high water accumulation in the fuel filter. Component LocationThe water-in-fuel sensor is integrated into the bottom of the OEM supplied suction fuel filter. 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...

Circuit DescriptionThe brake lamp relay is an OEM optional component used to illuminate the vehicle’s brake lamps under conditions when the engine is braking. Component LocationThe brake lamp relay is an OEM component. Refer to the OEM service manual for component location. 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 brake lamp relay driver circuit was shorted to high source or open circuit. Action Taken When the Fault Code is ActiveThe ECM illuminates the...

Circuit DescriptionThe brake lamp relay is an OEM optional component used to illuminate the vehicle’s brake lamps under conditions when the engine is braking. Component LocationThe brake lamp relay is an OEM component. Refer to the OEM service manual for component location. 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 brake lamp relay driver circuit was shorted to low source. Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE...

Circuit DescriptionAn engine oil pressure switch or oil pressure sensor is used by the engine control module (ECM) to monitor the lubricating oil pressure. For engines with an oil pressure switch, the switch is normally closed when the engine is not running and open when oil pressure is present. For engines with an oil pressure sensor, the ECM will detect a low signal voltage at operating conditions when the oil pressure is low. The ECM will detect a high signal voltage at operating conditions when the oil pressure is high. Component LocationThe engine oil pressure sensor is located in the...

Circuit DescriptionThe Engine Control Module (ECM) provides 5 volts to the intake manifold temperature signal circuit, and monitors the change in voltage caused by changes in the resistance of the sensor to determine the intake manifold temperature. When the intake air is cold, the sensor (or thermistor) resistance is high. The ECM signal voltage only pulls down a small amount through the sensor to a ground. Therefore, the ECM senses a high signal voltage or low temperature. When the intake air is warm, the sensor resistance is low. The signal voltage pulls down a large amount. Therefore, the ECM senses...