GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

General Information


Four different criteria have to be met before an engine can start and run.

Timing: This includes proper synchronization of the crankshaft and camshaft assemblies, proper installation of the timing mechanisms (chains or belts), proper operation of the valve train, and the proper installation and operation of the distributor to the timing marks; or the proper clearance and placement of the crankshaft and camshaft sensors.
Fuel: This includes the fuel tank and lines, fuel pump and regulator, gauge, carburetor or fuel injection system; it also includes ascertaining a fresh air supply and a clean supply of fuel, with the proper octane.
Compresion: This includes the proper fitting of the piston to the cylinder bore in the block. The proper seating of the rings in their grooves and the fitting of the valves in the manifold in order to form a tight seal.
Ignition: This includes the battery and starter circuits, ignition switch and wiring, the primary ignition circuit, the secondary ignition circuit (including spark plugs) and the electronic controls.

Since the Powertrain Control Module is programmed to recognize the presence and value of electrical inputs, it will also note the lack of a signal or a radical change in values. It will react, for example, to the loss of signal from the vehicle speed sensor or note that the engine coolant temperature has risen beyond acceptable (programmed) limits.

Once a fault is recognized, a numeric code is assigned and held in memory. The dashboard warning lamp: CHECK ENGINE or SERVICE ENGINE SOON, will illuminate to advise the operator that the system has detected a fault. This lamp is also known as the Malfunction Indicator Lamp (MIL).

More than one code may be stored. Keep in mind not every engine uses every code. Additionally, the same code may carry different meanings relative to each engine or engine family.

In case of a PCM failure, the system will default to a pre-programmed set of values, which allow the engine to operate, although at reduced efficiency. This is variously known as the default, limp-in or back-up mode. Driveability is always affected when the PCM enters this mode.