A False Code 42 may be caused by the routing of the EST wiring through and around spark plug ignition wires. The electromagnetic field around the spark plug wires is causing the False Code 42 to be set.
To correct the condition, route the EST wiring to the cowling side of the transmission fluid fill tube.
Another condition that may set a False Code 42 is by the cycling of the ignition switch 'ON-OFF-ON' without a pause in the 'OFF' position.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.