1999 GMC Savana Van Owner's Manual - Page 126

yellowblue This light should come on, as a check to show you it is working, when the ignition is on and the engine is not running. If the light doesn't come on, have it repaired. This light will also come on during a malfunction in one of two ways: NOTICE: Modifications made to the engine, transmission, exhaust or fuel system of your vehicle or the replacement of the original tires with other than those of the same Tire Performance Criteria (TPC) can affect your vehicle's emission controls and may cause the SERVICE ENGINE SOON light to come on. Modifications to these systems could lead to costly repairs not covered by your warranty. This may also result in a failure to pass a required Emission Inspection/Maintenance test. D Light Flashing -- A misfire condition has been detected. A misfire increases vehicle emissions and may damage the emission control system on your vehicle. Dealer or qualified service center diagnosis and service may be required. malfunction has been detected on your vehicle. Dealer or qualified service center diagnosis and service may be required. D Light On Steady -- An emission control system If the Light Is Flashing The following may prevent more serious damage to your vehicle: D D D D Reducing vehicle speed. Avoiding hard accelerations. Avoiding steep uphill grades. If you are towing a trailer, reduce the amount of cargo being hauled as soon as it is possible. 2-58