PROM - DTC 24 Set During California State I/M Test
File In Section: 6E - Engine Fuel & EmissionBulletin No.: 57-65-18
Date: September, 1995
Subject:
DTC 24 Set During California State Emissions Test (New Calibration)
Models:
1992 Chevrolet and GMC Truck S/T Models
with 4.3L V6 Engine (VIN Z - RPO LB4) and Manual Only Transmission (RPO MY2)
This Bulletin Applies To California Only.
Condition
Some California only owners may experience the Malfunction Indicator Lamp (check engine light) illuminates and may set a DTC 24 (VSS Circuit Fault) during a California State Emissions Test.
Cause
Some vehicles with mileage accumulation may have MAP levels below the 25 Kpa threshold during the 2500 RPM, transmission in neutral, portion of the test.
These conditions are used to identify a coastdown condition, during which there should be some vehicle road speed. Since there is no vehicle road speed during the emissions test, the DTC 24 may be set.
Correction
Calibrations, with the MAP threshold reduced from 25 Kpa to 20 Kpa for the DTC 24 test, have been released. The new calibrations do not affect vehicle emissions, and will detect a true Vehicle Speed Sensor (VSS) malfunction.
The MEMCALs are available for California vehicles described with the condition described above.
Service Information
Service MEMCALs are currently available from GMSPO.
Warranty Information
For vehicles repaired under warranty, use:
Labor Operation Labor Time
J6364 0.8 hr