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Interesting. My car will automatically downshift going down a hill but not until I tap the brakes. If I coast it will not downshift. It's never major engine braking. Just from 5th or 6th gear to 4th or 3rd.. I wonder what sensor is used to determine the angle of the vehicle. Sometimes the uphill not wanting to upshift is a lttle annoying. It will hold the lower gear a little too long.
Yeah I wondered it is was a faulty yaw sensor or something similar that determines the cars angle. I filmed the issue on my phone so I am hoping to post it up soon.
The shop manual points to the ECM if you have "No engine braking".
Perhaps you can borrow a known-working ECM from a friend (or the dealer), and try it out on your car to see if you can eliminate the problem. Here's where you will find your ECM.
Check this out. Look at the last post. One of those sensors may have failed. Where are they and can they be tested is the question.
Zero Point Calibration of Yaw Rate and Deceleration Sensors Using SST 09843–18040.
When having replaced the yaw rate sensor, deceleration sensor or the ECU, perform the process for zero point of yaw rate and deceleration sensors as shown below.....
More information on DLC3 terminal locations and SST 09843-18040 (which is essentially 2 short jumpers joined together to allow jumpering up to 3 terminals together). In this case, a paper clip or a short piece of wire will do the trick.
Lavrishevo, and rkw77080 you guys are the best! Thank-you so much! Just the info that you guys have found so far is more info than the Lexus dealer has been able to suggest or find in years!
...swapping it over would just be a matter of plugging it in, but I wonder if you have to do anything else before driving off coz I don't want to damage anything?
Thanks for everyone's help so far - I'm certainly not giving up now!
As a rule-of-thumb, any "electronic" work (such as ECU replacement) should be done with the battery negative cable disconnected. This will reset all ECUs back to their factory default settings.
This forum is filled with very informative and helpful folks - if you need reference material from Lexus shop manual, just simply ask! Please keep in touch and good luck...
LEX ES300, Assuming that you've manually enabled the "engine brake" by moving the shifting lever from "D" to "S" while going down hill and did not feel any "braking", you may be having CAN (Controller Area Network) communication problem with the ECM. However, just to be sure, please take a second look at the instructions on the Owner's Manual...
If you have followed the instructions and your engine does not rev up when it down-shift, then here are a couple of "Inspection Procedures" for you to consider before you take the plunge for a replacement ECM.
I've read thru most of these posts and have a question for you. Are you flipping the switch on the dash to active engine braking or are you actually using the console-mounted shift lever to cycle the the gears?
On a related note, I've noticed on many occasions that if I am driving on a slight downhill grade at 25-40MPH and tap the brake pedal, the car will retard the acceleration, all while in Drive. If I hit the gas, it resumes normally. I guess I am too lazy to read the manual to figure this feature out.
I've read thru most of these posts and have a question for you. Are you flipping the switch on the dash to active engine braking or are you actually using the console-mounted shift lever to cycle the the gears?
On a related note, I've noticed on many occasions that if I am driving on a slight downhill grade at 25-40MPH and tap the brake pedal, the car will retard the acceleration, all while in Drive. If I hit the gas, it resumes normally. I guess I am too lazy to read the manual to figure this feature out.
Hi peteyx, are you talking about the switch that says pwr, ect, snow? That is the only switch I have. I have tried it in pwr and even snow and nothing that resembles engine braking. I dont think that switch affects engine braking. Pwr does make acceleration better and more responsive. I am trying to use engine braking as per the manual by shifting the gear lever into 's' mode.
12-12-14, 04:28 AM
Thank-you so much! Just the info that you guys have found so far is more info than the Lexus dealer has been able to suggest or find in years! 
