Water In Fuel Indicator: Description and Operation

WATER - IN - FUEL INDICATOR

DESCRIPTION
A water-in-fuel indicator is standard equipment in all instrument clusters. The water-in-fuel indicator is located near the lower edge of the instrument cluster, to the left of the multi-function indicator display. The water-in-fuel indicator consists of the International Control and Display Symbol icon for "Water In Fuel" imprinted within a rectangular cutout in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the icon to appear silhouetted against an amber field through the translucent outer layer of the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The water-in-fuel indicator is serviced as a unit with the instrument cluster.

OPERATION
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. to the appropriate diagnostic information.