CODE 34 SET AT IDLE DIAGNOSTIC PROCEDURE. GMC Truck S15 Pickup - 4WD 1984

For 1990-2009 cars

# CODE 34 SET AT IDLE DIAGNOSTIC PROCEDURE

#### MODELS: 1984-85 S/T TRUCKS WITH 2.8L (VIN CODE B) ENGINES, MANUAL TRANSMISSIONS, AND CALIFORNIA EMISSIONS

Some 1984-85 S/T Trucks with manual transmissions and California emissions may set a Code 34 Check Engine Light after a short period of idling.

To determine cause of this condition, perform the diagnostic check for Code 34 in Section 6E7 of the Service Manual.

If the diagnostic check indicates a wiring problem, (grounded or open), correct as required. If the Code 34 condition persists, inspect for faulty connections at the differential pressure sensor and correct as necessary.

If the diagnostic procedure indicates a faulty differential pressure sensor, replace the prom with one of the following service proms. These proms allow for a greater amount of engine vacuum prior to setting a Code 34.

#### Model Year Service Prom

1984 1227896 1985 1227897

If the Code 34 condition continues after installation of the service prom, replace the differential pressure sensor.

Use applicable Labor Time and Operation Number.

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.