4L80-E INITIAL SERV. AND DIAG. INFORMATION

Subject: INITIAL SERVICE AND DIAGNOSIS INFORMATION

Model and Year: 1991 C/K, RN, G, P TRUCKS WITH 4L80-E (MT1) AUTOMATIC TRANSMISSION

TO: ALL CHEVROLET DEALERS

It is important that all transmission technicians become familiar with the HYDRA-MATIC 4L80-E section of the service manual. The 1991 service manuals contain three sections with information on the HYDRA-MATIC 4L80-E. A video tape will be sent to each Chevrolet dealership during October.

SERVICE MANUAL REFERENCE:

DIAGNOSIS - In Section 7A2: Contains road and hoist test, line pressure test, Torque Convertor Clutch (TCC) diagnosis, clutch application chart, electrical, mechanical and hydraulic diagnosis information.

ON-VEHICLE SERVICE - In Section 7A2: Contains service procedures that can be performed with the transmission still in the vehicle. This section also shows how to remove and install the HYDRA-MATIC 4L80-E transmission.

ELECTRONIC TRANSMISSION CONTROL - In Section 7A4: Contains explanations of each electronic component and how they fit into the control system. All malfunction code diagnosis trouble trees are contained in this section.

UNIT REPAIR - In the Light Truck Unit Repair Manual: Contains complete bench disassembly and reassembly procedure.

VIDEO TAPE - This video tape provides the technician with a brief overview of the 4L80-E and the differences between the 3L80 and the new components of the 4L80-E. This 16 minute tape outlines a basic diagnosis path required for the new era of electronic transmissions.

DIAGNOSIS INFORMATION:

If a HYDRA-MATIC 4L80-E is brought in for service, follow the diagnostic procedure contained in the Automatic Transmission Diagnosis in Section 7A2 of the 1991 Service Manual.

IMPORTANT: Use all diagnosis information to carefully determine whether the problem is with the external control system (electronic components) or an internal hard part. Also make certain that the engine and its sensors are performing properly.

If the problem is determined to be an electronic component or an on-vehicle service item, the replacement part may be ordered through GMSPO on a VIP order.

If the problem is determined to be an internal hard part, i.e. metal or friction material is found in the pan, SRTA units should be utilized unless the following two conditions are met.

- Essential technician training has been completed by dealership personnel and - Special tools are in the dealership.

ESSENTIAL TOOLS:

The complete 4L80-E essential service tool package will be shipped to dealers starting December 15, 1990. If for some reason your dealership should have a need for a set of essential tools to resolve a vehicle down situation and your tool shipment has not arrived, you should contact your Zone service representative. An emergency shipment of 4L80-E tools will then be expedited on a 24 hour basis. The dealer then will NOT be shipped a duplicate set of tools at a later date.

TRAINING CLASSES:

Service Technology Group (STG) training classes required for service of the 4L80-E:

Class Description Number Duration Availability ------------------ -------- ---------- ------------- Transmission and Brakes 18001.07 Four Days Current Electronics Training or GM Specialized 18001.02 Eight Days Current Electronics Training

4L80-E Overhaul 17001.17 Three Days December 1990 Training

Prerequisites:

ASE Automatic Transmission Certification or Any GM Training Center Automatic Transmission Class

Transmission and Brakes Electronics Training or GM Specialized Electronics Training must be taken before 4L80-E Overhaul Training.

All dealers are expected to have completed essential training for the 4L80-E by March 31, 1991. After essential training has been completed, the SRTA program should be utilized per the general guidelines of replacement versus overhaul.

SERVICE PARTS INFORMATION:

Electronic components or on-vehicle service parts are available through GMSPO on a VIP basis. SRTA ordering information can be obtained in Dealer Service Bulletin No. 9l-9O-7A.

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.