Aftermarket (Add-On) Electrical And Vacuum Equipment
Aftermarket (add-on) electrical and vacuum equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the vehicles electrical or vacuum systems. No allowances have been made in the vehicle design for addition of this type of equipment.
Add-on electrical equipment may cause the engine control system to malfunction even when the add-on electrical equipment is installed properly. Portable telephones and radios may also cause engine control system malfunctions even when not connected to the vehicle's electrical system. The first step in diagnosing any engine control system problem is to remove all aftermarket electrical equipment from the vehicle. Diagnosis may proceed in the normal manner after eliminating aftermarket equipment as a cause of the engine control system malfunction.