Mechanics

OVERDRIVE PROBLEM

1992 Toyota Previa

Transmission problem
1992 Toyota Previa 4 cyl Two Wheel Drive Automatic

Recently my Previa has been shifting in and out of overdrive. Sometimes only sporadically, more often it is beginning to shift in and out every 1 or 2 seconds. When I push the overdrive button to turn it off, it runs ok, but I can still feel a sort of 'chugging', but not anything like the shifting in and out when in overdrive, which becomes a head banging, neck jerking experience. I took it in for service to a transmission specialist. No codes appeared faulty on the diagnostics, so on a 'hunch' they replaced the throttle control valve. This did not fix the problem. They told me it may be an electrical/electronic issue that they were not capable of assessing, possibly requiring a new computer. Any suggestions?
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Doophus
November 2, 2009.



Hi doophus,

Thank you for the donation.

Perform the following and see if you can come up with anything. Monitor is the trans slips when shifting into OD when shifting into D. Repeat a few times to be sure.

TRANSMISSION SHIFT TESTING

NOTE: Perform manual shifting test if no fault codes exist. Manual shifting test determines if problem area is in electrical circuits or a mechanical transmission problem.

1 . With ignition off, disconnect electrical connector for solenoids from rear of transmission. See Fig. 7 .


http://www.2carpros.com/forum/automotive_pictures/192750_ManualShift92PreviaFig07_1.jpg



2 . Road test vehicle and ensure transmission gear changes corresponds with shift lever position. See GEAR APPLICATION table.

3 . If abnormality exists, a mechanical transmission problem exists. If all gears are correct, perform trouble shooting in accordance with the symptom. Turn ignition off.

4 . Reconnect electrical connector. Clear fault codes from ECT ECU memory, as disconnecting electrical connector may set a fault code.


http://www.2carpros.com/forum/automotive_pictures/192750_ManualShiftTest_1.jpg




KHLow2008
Nov 2, 2009.