NO 3-4 UPSHIFTING (DISCONNECT CRUISE CONTROL SWITCH TO PCM

Subject: NO 3-4 UPSHIFT (DISCONNECT THE CRUISE CONTROL SWITCH TO THE PCM)

Model and Year: 1993 C/K TRUCKS AND G VANS WITH 6.2L DIESEL ENGINE

CONDITION:

--------- Some 1993 vehicles equipped with the HYDRA-MATIC 4L60-E transmission and 6.2 liter diesel engine may not obtain 4th gear when cruise control is engaged and vehicle speed is above 63 mph. If the vehicle is in 4th gear at highway speeds with cruise control on and the transmission downshifts when going up a hill or if the driver manually downshifts to drive and then back to overdrive, the transmission may not return to 4th gear.

CAUSE:

----- If the vehicle is at highway speeds with cruise control on, and a 4-3 downshift is forced due to increased road grade. The vehicle then returns to stable or level road grade, a 3- 4 upshift may not occur, due to the throttle position.

CORRECTION:

---------- To improve the 3-4 upshift condition, the white wire (85) from the cruise control switch to the PCM (B10) must be disconnected.

NOTE: The PCM uses this signal to represent the status of the cruise control. The PCM uses this information to modify the shift schedules and TCC schedules when cruise has been requested. If the white wire (85) is disconnected, the vehicle may exhibit a busy condition with TCC.

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.