Harsh Engagement of the Driving System in A/T Vehicle


The symptoms relating to strong shocks in the driving system in an A/T vehicle can roughly be separated into two types.
• Only shock is sensed
• Both shock and sound are sensed When both shock and sound are sensed, even if the shock itself is not strong, since the sounds which is sensed by the ears and the shock which is sensed by the body are synchronized, the degree of complaint tends to be large. The conditions in which a strong shock occurs varies depending on the causes, such as starting, shifting, accelerating, sudden throttle opening and closing, etc. When proceeding with troubleshooting for strong shock in an A/T vehicle, it is necessary to pay attention to the following.
• It is important to judge whether the shock is malfunction level or not, because a certain shock is not avoidable when shifting due to the construction and function of A/T vehicle. To be able to judge accurately, it is important to drive an A/T vehicle on a daily basis in order to become familiar with the level in each model, so as to develop a good sense of judgement regarding whether it is a malfunction or not.
• As for the cause of the strong shock, the malfunction area can be signifi cantly narrowed down based on the malfunction occurrence conditions. A cause other than an A/T can also be considered, so it is important to understand the occurrence conditions and problem symptoms accurately. When using an unspecifi ed ATF, it negatively affects the shock when the clutch engages or slips, so it is important to use the specifi ed one. As the coeffi cient of friction becomes larger, the greater the shift shock will be.
1. Basic inspection
Inspection methods
Perform “Basic Inspection” in the Repair Manual.
2. Conformity with the result of the DTC output (ECT)
Even if the DTC indicates abnormality, the malfunction that the DTC indicates is different from the malfunction that the customer points out. Therefore, inspect the relationship between the DTC and the problem symptom.
Normal DTC is displayed
The cause of the malfunction can be estimated in the area that has no DTC.
DTC is displayed
Check the conformity between the output result of the DTC and the problem symptom.
No DTC is displayed
When no DTC is displayed, the ECU itself can be considered not to operate properly. Therefore, the malfunction can be judged to be in the power source or the relevant area.
• DTC and problem symptoms When DTC is detected, the code may be related to the shock reducing control. But, the contents greatly affect the engine or ECT control, other symptom problems may be accompanied by the malfunction. For example, when IDL contact is always OFF, the malfunction of the engine hunting or idling speed failure is more signifi cant than that of the shock when shifted from N to D position. In the DTC that is related to ECT relevant area, if the S1 or S2 solenoid valve relevant area DTC is output, the symptom may rather be felt shifting point failure or insuffi cient power than the strong shock.
3. Narrow down whether A/T or others according to road test
Hold the gear in position, so as not to shift it, and verify whether the shock occurs or not when accelerating and decelerating. Narrow down whether the malfunction cause is in the A/T itself or in other areas. If the shock occurs under this condition, the cause can be judged to be in the driving train and suspension devices, that is not in the A/T. In this case, gear noise may be accompanied by shock.
Causes other than A/T
Drive train and suspension failures
• Engine mount failure
• Rattle and play of propeller shaft and drive shaft are large
• Backlash in the differential is large
• Suspension installation condition is bad
4. Narrow down by occurrence condition and inspection result
The occurrence of a strong shock caused by the A/T itself, happens only when shifting. Therefore, based on the shock occurrence conditions, considering what the acting elements are or what commonly occurs can narrow down the cause.
Strong shock when both the shift lever is moved and the gear is changed
It is considered that the cause is not in each acting element but in the line pressure, which in relation to all the acting elements, is excessively high.
If this occurrence timing is same as the ATF changed timing, wrong ATF may be used.
Line pressure adjustment
Line pressure changes depending on the number of the throttle valve E ring.
Adding one E ring reduces approximately 0.2 kg/cm

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