DIAGNOSIS AND TESTING - ROAD TEST

Prior to performing a road test, verify that the fluid level, fluid condition, and linkage adjustment have been approved.

During the road test, the transmission should be operated in each position to check for slipping and any variation in shifting.

If the vehicle operates properly at highway speeds, but has poor acceleration, the converter stator overrunning clutch may be slipping. If acceleration is normal, but high throttle opening is needed to maintain highway speeds, the converter stator clutch may have seized. Both of these stator defects require replacement of the torque converter and thorough transmission cleaning.

Slipping clutches can be isolated by comparing the “Elements in Use” chart with clutch operation encountered on a road test. This chart identifies which clutches are applied at each position of the selector lever.

A slipping clutch may also set a DTC and can be determined by operating the transmission in all selector positions.


ELEMENTS IN USE AT EACH POSITION OF SELECTOR LEVER

Shift Lever Position
  		 INPUT CLUTCHES
  		 HOLDING CLUTCHES
  
Underdrive
  		 Overdrive
  		 Reverse
  		 2/4
  		 Low/Reverse
  		  
P - PARK
  		         X
  
R - REVERSE
  		     X
  		   X
  
N - NEUTRAL
  		         X
  
OD - OVERDRIVE
  		          
First
  		 X
  		       X
  
Second
  		 X
  		     X
  		  
Direct
  		 X
  		 X
  		      
Overdrive
  		   X
  		   X
  		  
D - DRIVE*
  		          
First
  		 X
  		       X
  
Second
  		 X
  		     X
  		  
Direct
  		 X
  		 X
  		      
L - LOW*
  		          
First
  		 X
  		       X
  
Second
  		 X
  		     X
  		  
Direct
  		 X
  		 X
  		      
* Vehicle upshift and downshift speeds are increased when in these selector positions.
  

The process of elimination can be used to detect any unit which slips and to confirm proper operation of good units. Road test analysis can diagnose slipping units, but the cause of the malfunction cannot be determined. Practically any condition can be caused by leaking hydraulic circuits or sticking valves.