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Transmission Downshifting Intermittently


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For the past 6 days or so my 95 lexus es 300 was exhibiting some weird transmission problems, or so i thought. While cruising at highway speeds the transmission would intermittently downshift to 2nd gear without any cause. I normally drive with overdrive off. If overdrive was on it would downshift to third again intermittently. Also, sometimes i would notice the car wouldn't take off normally. It felt like i was starting off in 2nd gear sometimes. Of course their were no trouble codes and the fluid was at the correct level. If cruise was set and it started acting up i would notice the vehicle would not hold a speed and then all of a sudden speed up to where it was originally set. Finally, my problem started to become more frequent. I used to work on toyotas so i had my scan tool and viewed the live data while my wife drove the vehicle. Of course the car didn't act up and everything looked good. When i got home i let the car idle and i noticed that the pitch of the engine was changing erratically. I viewed the live data and saw the vehicle speed signal was jumping from 0 mph, which it should read while parked, all the way up to 180 mph and then back to 0 then back to 118 mph just randomly while the car was parked siting at idle. I went to toyota and bought a new vehicle speed sensor. This is mounted on top of the transmission near the firewall and is secured by one bolt. It just pulls out. It costs about $250.00. I hope this fixes the problem. I forgot to mention that i do have about 180,000 miles on the car and it is still going strong. When this problem did occur the speedometer did not fluctuate and read the correct speed at all times, and i only found the vehicle speed was out of range with the use of a scan tool. I'm assuming while driving the speed signal would either readover 140 mph and so the computer would cut the gas as a governor would on a sports car, and sometime the signal may have showed 0 mph and so the computer would downshift to the next lowest gear. After replacing it tonight i will see if it shifts properly for a week or so. Then i will know it's fixed. I hope this post might help some people that have a similar problem. My dealer told me that they had been selling alot of vehicle speed sensors lately so it may be a common problem.

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Replacing the sensor literally takes about 10 minutes to replace, but diagnosing the problem is where the expense lies. To replace the sensor I would expect an 1.0 labor if you tell them you just want that sensor replaced. If you want it diagnosed it could be several hours labor depending on how intermittent your problem is. Most dealers are close to $100.00 an hour labor. If you take it to a dealer and you get a mechanic who has experienced the same problem you are having then he can fix it faster and cheaper. I would expect it to be between $350.00 to $500.00 at a dealer for the whole repair.

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