MIL ON, DTC 34 (Differential Pressure Senor) Set
86chevy16NUMBER: 86-B-95
GROUP: 6D - Engine Electrical
DATE: June, 1986
SUBJECT: CHECK ENGINE LIGHT (CODE 34) AFTER A SHORT PERIOD OF IDLING
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 idlng. 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.