Engine Controls/Emissions - Hesitation/A/T Slipping

TSB SB04-02-S001

Intermittent Hesitation, Stumble or Idle Stall After Soak, Harsh 1-2 Shift, Slipping 1-2 Shift Followed By A Harsh Engagement (Reprogram PCM)

Issue Date: February 2004

Affected Vehicles
2003 Isuzu Ascender equipped with 4.2L engine (VIN S - RPO LL8).

Service Information

Condition:
Some customers may comment on an intermittent hesitation/stumble or idle stall within minutes of starting after the vehicle has been sitting for several hours. Additionally, some customers may comment on a harsh 1-2 shift or 1-2 slip shift that has a bump feeling when 2nd gear engages.

Possible Cause:
This condition may be caused by the EVAP diagnostic test as it opens the purge valve for a few seconds and then closes it to verify proper emission sensor operation. If the purge canister is saturated, the EVAP system on-board diagnostic test may cause the vehicle to correct for a rich condition from the canister. The vehicle would then become lean when the purge valve closes at the completion of the test. This condition occurs primarily with high *Reid Vapor Pressure (RVP) fuel and when a vehicle has been sitting for several hours in a warm ambient, above 21 °C (70°F). A customer who takes short trips is more likely to experience this condition, as they do not have the drive cycle that would allow the purge canister to fully recirculate the fuel vapor.

* A method of determining vapor pressure of gasoline and other petroleum products. Widely used in the petroleum industry as an indicator of the volatility (vaporization characteristics) of gasoline.

Correction:
Follow the diagnostic and reprogramming instructions in the service procedure below.

Service Procedure

1. For Hesitation, Stumble or Idle Stall:

^ Follow the Service Manual diagnostics for the stall/stumble condition. If the result is no trouble found then reprogram the module with the latest calibration.

2. For Harsh or Slipping Shifts on 2003 Model Year vehicles:

^ Reprogram the module with the latest calibration.

NOTE:
The latest calibrations are available on ITCS #28 or later.

Warranty Claim Information





Use the labor operation shown.

Labor Time includes administrative time allowance.

Warranty Claim Information





Use the labor operations shown:

Labor Time includes administrative time allowance.





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