Es300 Transmission Electronics

[NavyPhil]

Lexus 1996 ES300 (217k miles) Transmission Problems

Non-Automotive engineer (but years of computer experience) needs help.

Situation: About 6-7 weeks ago, while backing from driveway, the Overdrive (OD) disengage light came on, partially. Backlit in gray vs. usual yellow when fully OD disengaged. OD Light then gradually went back to dark. Car then failed to up-shift as speed increased to highway speeds. RPM’s showed significant increase. Car obviously straining at 65MPH. Stopped at my Mech shop which specializes in Acura, but has one Lexus-certified mech..

Local (trusted, non-dealer) mechanic tested, and repaired/replaced/troubleshot as cited:

‘Repaired multiple issues with SL/Overdrive circuit. Replaced wiring harness (TOY8412)with repeated shorts in it. Replaced ECU (BW452136) and reprogrammed as required. Rechecked…and found continued cycling short with SL control solenoid. Replaced SL control solenoid within valve body and checked for proper operation. Reassembled and reset engine specs. All normal. Extensive road test. Normal ops.’

In numerous verbal discussions with the shop owner, provided more details on processes used, including a visit to a local east coast Tranny shop, whose solution was to “replace the transmission”($3,000++) , until the question was asked, “Who pays if this does not solve the problem?” Recommendation was withdrawn. Mech says all pressures within unit are right on spec. It is not mechanical.

Car back to me. These actions brought back to normal operations for several days. Problem has now resurfaced. Mech has over 30 hours total time in diagnosis and repair. Has billed me for 5. I’ll have no more charges. Wants to take the car to local Lexus dealer for their “formal” assistance at his expense.

Anyone know of a structured (ISO-type) diagnosis process for isolating ECM/SL/Transmission control system electronic/electrical interfaces to isolate this “bug”? It does not appear to be heat or distance related. It did first occur after the car was (safely) driven through a torrential downpour. (Appears that the flex exhaust pipe with catalytic converter is also in need of replacement. Any way converter-related??)

Any assistance appreciated. This shop owner is a good guy and I would like to save him some money if possible.

[lenore]

Could still be transmission....The valve body in a transmission is like the clean room on the space shuttle...Debris can stop the proper piston movement and eventually score the soft aluminum sides of the piston bores...The pistons hang up and cause improper shifting etc. A flush will not fix the problem...The debris is usually from poor maintenance or a failure inside the transmission...ie planetary gears wear out the the filings contaminate the filter and valve body assembly...at that point the transmission needs a rebuild...I personally tried to save mine (RX300) by removing the valve body and cleaning, but the gear failure was too much...Whatever you do dont do a flush...Drain and fill only on these tranny's....Now your car is quite aged, and yes the solenoid could have failed along with the wiring degenerating....But my bet it is tranny time. good luck

seriously doubt the flex pipe and converter would cause you a problem unless you have codes present which may put the transmission in limp mode until the codes are cleared...Shoot unplug the battery for 10 minutes and reconnect and see if the problem goes away.

[Mike B.]

If there is a problem with a shift solenoid or piston hanging up it should set a code. Sounds to me like the only symptom is a failure to engage overdrive. If so, there could be an internal issue with the torque converter which would not trip a code and would not show up in a pressure test. Would need to hook up a toyota scan tool (not a generic/aftermarket of any kind) and drive it around while checking streaming data.