Water-In-Fuel Indicator: Operation

WARNING: This page is about a different car, the 2006 Dodge Sprinter. However, it is still accessible from the selected car via links, so may be relevant.

The water-in-fuel indicator gives an indication to the vehicle operator when there is excessive water detected in the fuel filter. This indicator is controlled by a transistor on the instrument cluster circuit board based upon the cluster programming and electronic messages received by the cluster from the Engine Control Module (ECM) over the Controller Area Network (CAN) data bus. The water-in-fuel indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster detects that the ignition switch is in the On position. Therefore, the LED will always be off when the ignition switch is in any position except On. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the water-in-fuel indicator for the following reasons:

Bulb Test - Each time the ignition switch is turned to the On position the water-in-fuel indicator is illuminated for about seven seconds as a bulb test.
Water-In-Fuel Lamp-On Message - Each time the cluster receives a water-in-fuel lamp-on message from the ECM indicating that there is excessive water in the fuel filter with the engine running, the water-in-fuel indicator will be illuminated. The indicator remains illuminated until the cluster receives a water-in-fuel lamp-off message, or until the ignition switch is turned to the Off position, whichever occurs first.

The ECM continually monitors the water-in-fuel sensor to determine whether there is excessive water in the fuel filter. The ECM then sends the proper water-in-fuel lamp-on and lamp-off messages to the instrument cluster. If the water-in-fuel indicator remains illuminated with the engine running, excess water should be drained from the fuel filter. If the indicator remains illuminated with the engine running after the water has been drained from the fuel filter, it may indicate that a malfunction has occurred in the water-in-fuel sensor or circuits. The ECM will store a Diagnostic Trouble Code (DTC) for any malfunction it detects. For proper diagnosis of the water-in-fuel sensor and circuits, the ECM, the CAN data bus, or the electronic message inputs to the instrument cluster that control the water-in-fuel indicator, a diagnostic scan tool is required. Refer to BODY DIAGNOSTIC PROCEDURES .