Instantaneous Fuel Economy Always Reads "0" Miles/Gallon Or "99" Liters/100 Km

Verify speedometer is operating properly. If okay, go to next step. If not, go to SPEEDOMETER READS "0" MPH WHEN VEHICLE IS IN MOTION test.
Remove instrument cluster. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION in this article. Check continuity between pin "10C" of speedometer and pin "18A" of fuel computer. See INSTRUMENT CLUSTER PIN CONNECTOR IDENTIFICATION illustration. If okay, replace fuel computer module. If not, repair wiring in circuit as necessary.