1-2 SHUDDER/CHUGGLE OR DOUBLE BUMP
SUBJECT: 1-2 SHUDDER, CHUGGLE OR DOUBLE BUMP
MODELS: 1991 C/K, R/V, P LIGHT DUTY TRUCKS AND G VANS WITH 4L80-E/4L80-EHD AND 6.2L DIESEL ENGINES
SERVICE INFORMATION
Some 6.2L Diesel HYDRA-MATIC 4L80-E/ 4L80-EHD Transmissions with either 100 AMP or 105 AMP alternators (RPO's K60 and K68, respectively) may experience a 1-2 shudder, chuggle or double bump. This condition is created by excessive transmission line pressure oscillations caused by the force motor circuitry short protection transistor Q6 which is located within the T.C.M. (Transmission Control Module).
A new T.C.M. package has been released that eliminates this condition.
DATE OF PRODUCTION CHANGE (see Figure 1)
Starting October 23, 1990 (Julian Date 296) all CAP, CBP, CKP and CRP HYDRA-MATIC 4L80-E/ 4L80-EHD transmission models were built with this new Transmission Control Module.
SERVICE PROCEDURE
Diagnostics of this situation involves disconnecting the 4-wire connector on the alternator and duplicating the complaint. Should the complaint be alleviated by the above procedure, a new T.C.M. will have to be installed. Refer to your 4L80-E Diagnosis Section of the Service Manual if the condition still exists.
SERVICE PARTS INFORMATION
Part Transmission Number Description Models -------- ------------------------ ------------ 16147609 Pkg.-Transmission Control CAP, CBP, Module/with Instruction CKP, CRP Sheet
Part is currently available from GMSPO.
SERVICE MANUAL REFERENCE:
Refer to appropriate service manual replacement procedures.
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.
