Canada - A/T - Automatic Transaxle Diagnosis
GROUPTRANSAXLE
NO
00-40-005
DATE
SEPTEMBER 22/00
MODEL
ALL
SUBJECT
AUTOMATIC TRANSAXLE DIAGNOSIS
The purpose of this bulletin is to review key points which must be adhered to when performing a diagnosis on an automatic transaxle, with the intent to reduce the number of "No Defect Found" transaxles received by HAC's remanufacturing facility.
It is important for dealer Service Department personnel to understand the shift characteristics of Hyundai automatic transaxles in order to make a determination if a customer complaint of harsh shifting is justified or not.
CURRENT DESIGN CHARACTERISTICS
As with all automatic transaxles, a certain amount of slippage occurs between the friction elements (clutches and brakes) when different gear ratios are being selected. If too much slippage occurs between friction elements within the transaxle during a gear change, the net result will be a smooth shift, but over time, excessive and pre-mature wear will occur to the friction elements.
Hyundai automatic transaxles are inherently designed with relatively "crisp" upshifts upon acceleration, and downshifts under hard acceleration. This characteristic is the result of minimal slippage between friction elements during the upshift or downshift, thus optimizing engine performance and minimizing friction element wear.
With the advent of increasingly sophisticated automatic transaxles in new models such as the EF Sonata and Accent, which incorporate "fuzzy logic" in the Transaxle Control Module, that actually adapt to driver habits, and a number of refinements to the overall transaxle design, gear shift quality and feel are much improved, with no compromise to engine performance or friction element longevity.
CUSTOMER TEST DRIVE
It is very important for Dealership Service Personnel to explain the operating characteristics of Hyundai automatic transaxles to a customer when faced with a complaint regarding shift quality. A test drive with the customer is of vital importance to see first hand if the complaint is warranted or not. It is sometimes helpful in explaining inherent automatic transaxle shift characteristics to take the customer for a ride in a similar model vehicle from the dealer's inventory in order to further demonstrate this point.
DIAGNOSIS
The following points are also important when performing an automatic transaxle diagnosis:
1. Basic troubleshooting procedures are the same for all concerns, whether they apply to engines, transaxles or electronic components. Always follow an organized troubleshooting and diagnostic procedure:
^ Verify the concern
^ Isolate the source of the problem
^ Identify the faulty component
^ Make the repair
^ Verify the repair
2. When conducting a diagnosis, the Technician should repair any leaks and perform a road test before checking for diagnostic trouble codes (DTC). Always resolve electrical codes before trying to fix conditions associated with mechanical conditions.
Since all current generation Hyundai automatic transaxles are electronically controlled, you should use the Hi-Scan Pro to diagnose the electrical circuits and check for DTCs. Keep in mind that if a DTC is retrieved, in the majority of cases the problem can be traced to an electrical component associated with the transaxle. If scan tool results are abnormal, there are several possibilities that should be reviewed as follows:
^ Check the TCM terminal connections for tightness
^ Check for corrosion in terminals
^ Check for pinched or broken wires
^ Check for poor grounds
3. When performing an automatic transaxle diagnosis, follow all steps outlined on the "ATM Diagnostic Flow Chart" and "ATM Diagnostic Questionnaire" (Part # 000SA-94001 - English and 000SF-94001 - French). The ATM Diagnostic Flow Chart is designed to be complete and comprehensive. If you skip a step in the flow, you cannot rely on the results of your diagnosis. Don't assume you already know the answer for a concern, or skip steps to save time.
Refer to technical training course # 312 Automatic Transaxle Diagnosis for complete details on utilizing the ATM Diagnostic Flow Chart and ATM Diagnostic Questionnaire.
4. It is imperative for the Service Advisor to attain a complete and accurate description from the customer of the complaint. It is equally important that the Service Advisor reports fully whatever the customer tells them. Keep in mind that the customer may not describe a condition in terms which will be most helpful to you. If the customer describes the condition as "low power", the transaxle may be in the fail safe mode, causing the vehicle to accelerate in 3rd gear. The Service Advisor must sometimes translate the customer's description into something which is technically meaningful.
5. Hyundai provides a number of different tools to help you diagnose and repair transaxle concerns including:
^ Hi-Scan Pro
^ Automatic Transaxle Tester (refer to TSB Group Transaxle No. 9940-006 for Automatic Transaxle Tester II operating instructions)
^ Automatic Transaxle Oil Cooler Flusher (refer to TSB Group Transaxle No.9940-006)
You must be able to operate each of these tools skillfully before you diagnose and repair automatic transaxle related concerns, and to avoid comebacks.
6. The Hi-Scan Pro should be used to monitor the following components:
^ Pulse generators
^ Throttle position sensor
^ Oil temperature sensor
^ Kickdown switch
^ Accelerator switch
^ Vehicle speed sensor
^ Inhibitor switch
^ Overdrive switch
^ NC relay
^ Shift control solenoid valves
If any DTCs are detected, correct the problems before using the Transaxle Tester.
7. Technical training course # 312 Automatic Transaxle Diagnosis contains important test worksheets pertaining to evaluation of solenoid valves, throttle position sensor adjustment and tests, and pulse generator testing.