1995 Lexus ES 300 Transmission Shift

1995 LEXUS ES 300
132,000 MILES • 6 CYL • FWD • AUTOMATIC
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ALTEIXEIRAJR
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The transmission seems to not "know what gear to shift into"; the car will run fine for a short time, then the car will suddenly shift into neutral when running at constant speed. Other times, the car will not shift from low to high gears when pulling away from intersections, etc. , other times it will not down shift as I am slowing to stop at a red light.

A transmission mechanic told me it is not the transmission, and another mechanic told me it is not the speed sensors. The transmission mechanic said the main computer is not reading the speed sensors.

I can sometimes drive the car for short distances by manually up-shifting and down-shifting; however, at constant speeds the car cycles in and out of neutral.
Jun 27, 2015 at 4:57 PM
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KHLOW2008
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Are there any diagnostic trouble codes?
Jun 28, 2015 at 4:54 AM
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ALTEIXEIRAJR
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The check engineer light is always on, and the dash indicator that indicates which mode the transmission is set for: power or economy indicates that the mode cannot be set.

As for codes, I am told by my mechanic, that the code indicates a speed sensor not working; he did not give me the actual code number.

The transmission mechanic was the one who confirmed the speed sensors are working and that the main computer is not reading the sensors' output.

In fact, the transmission mechanic showed me the output from the sensors showing that they are providing speed information and he showed me that the car's computer shows 0 for the data from the sensors.

A website I was studying mentioned the LS400 exhibiting the same characteristics as my ES300; the information there indicates that the ECM has one or more bad capacitors and once replaced the transmission problems were solved for the LS400. I was wondering if this could be a possible root cause.

I also read yesterday that someone claimed a bundle of wires in the trunk can become shorted-out due to opening and closing of the trunk; this website claims this is a known issue with the ES300. Do you know if this is a possible root cause?

Regards,

A Teixeira
Jun 28, 2015 at 10:54 AM
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KHLOW2008
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If the Check Engine Light is indicating, the PCM has detected a fault within the system. since the code shows a speed sensor fault but the speed sensor is working, the problem most probably stems from the PCM. Remove the PCM and check the circuit board for leaking capacitors. If any found, replacing it should work.
Jul 2, 2015 at 10:32 AM