Emissions - On-Board Diagnostic System Correction

File In Section: 6E - Engine Fuel & Emission

Bulletin No.: 77-65-23

Date: November, 1997

Subject:
On-Board Diagnostic (OBD) System Improvements
(Re-flash Calibration)

Models:
1997 Chevrolet and GMC C/K, P Models
with 5.7L V8 Engine (VIN R - RPO L31) and
Automatic Transmission (MT1)





with the VIN Breakpoints as shown:

While the subject vehicles have been certified as complying with the applicable U.S. Environmental Protection Agency (EPA) and California Air Resources Board (CARB) On-Board Diagnostic (OBD) requirements, we have identified an OBD system improvement that should be implemented whenever practical.

Condition
Engine misfire diagnostics have been inadvertently disabled.

Cause
Some vehicles were released with software which inadvertently disabled the misfire diagnostics.





Correction
Use a Tech II to verify what software is programmed into the vehicle VCM. If the improved software has not been installed, reprogram/re-flash with the updated software. Refer to the listed table for the appropriate calibration changes.

Important:
Inform customers that this work is being performed on their vehicles to improve on-board diagnostic system operation and does not affect vehicle durability, reliability, or performance.

Calibration Information
The calibrations listed are FLASH calibrations and NOT available from GMSPO. Service FLASH calibrations are available starting with the 1997 Number 5 CD ROM.

Warranty Information
For vehicles repaired under warrant use:

Labor Operation Labor Time
J-6355 0.4 hr

Important:
This labor operation is covered under either the Federal or California Emission Control System Warranty (which-ever applies) or the Bumper-to-Bumper coverage in the New Vehicle Limited Warranty. The warranty with the broadest coverage applies.