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Engine Compression/downshift


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I have a 2008 rx350 with about 4500 miles.

I notice when you are slowing down as when approaching a line of traffic there is what I call engine compression that feels like it is down shifting. This is similiar to a manual transmission when you down shift under similiar circumstances but with the Lexus it is not as noticable as with a manual.

Does anyone know with these cars if that is how the transmission is set up. I have had no experience with a Lexus before.

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Yep, that is what the transmission is designed to do. You might do a search of the LOC site to get more information about quirky transmission issues. There is plenty of information here.

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I have a 2008 rx350 with about 4500 miles.

I notice when you are slowing down as when approaching a line of traffic there is what I call engine compression that feels like it is down shifting. This is similiar to a manual transmission when you down shift under similiar circumstances but with the Lexus it is not as noticable as with a manual.

Does anyone know with these cars if that is how the transmission is set up. I have had no experience with a Lexus before.

Do you really mean "downshifting" into a lower gear and thereby incurring a significant level of engine compression braking??

The majority of complaints, TONS OF THEM, going all the way back to the initial introduction of the RX series, and eventually involving the entire Toyota/Lexus fleet of FWD and F/AWD (Front engine torque biased AWD) involves a feeling of being bumped slightly from behind as you slow, throttle closed coastdown, to a stop 10-0 MPH, or a "slingshot effect" at 40-30 MPH with throttle closed.

It would be nice to hear that you are correct and they have finally addressed the issue of the lack of engine compression braking. Or may they're just following Ford's lead for their FWD hybrids and only allow regenerative braking (engine compression braking) if the OAT is significant above freezing.

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Yep, that is what the transmission is designed to do. You might do a search of the LOC site to get more information about quirky transmission issues. There is plenty of information here.

I am interested in learning more about this quirk. I thought it was just me, but the more I read this board I realize we have all have the same car with the same quirks.

What is the LOC site?

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  • 1 month later...

I HAVE THE SAME PROBLEM WITH MY 08 RX.PAID ALMOST 45K,THE DLR.SAID IT'S NORMAL FOR THE RX AND OTHERS TO SHIFT THAT WAY,BUT ,HE SAID, IF THEY DISCOVER A FIX FOR IT THEY WILL NOTIFY ME. I'M STUMPED. IF IT'S MORNAL, WHY WOULD THEY BE LOOKING FOR A FIX ? THE TRANS FEELS LIKE IT SLIPS AT A SLOW DOWN SPEED OF ABOUT 25-30 I CAN FEEL IT SHIFT OUT BY ITSELF,WHEN IT DOES I ACCELERATE AND CAN FEEL IT SLIP. DLR.CALLS IT A HESITATION CAUSED BY A FLY BY WIRE,SINCE 01. I THINK HE'S ON DRUGS.

BROUGHT IT BACK 3 TIMES FOR THIS PROBLEM.NOTHING WRONG THE 1ST. TIME.

2ND. TIME THE EASTERN REP CHECKED IT OUT AND SAID THERE IS NO POSSIBLE FIX FOR IT,WHEN THERE IS , THEY WILL CALL.

3RD. TIME THEY CANT DUPLICATE IT ( SOUNDS FUNNY TO ME )

85OOK LATER SAME PROBLEM.AND YES ROOF RACK RAILS ARE LOOSE,NOT DESIGNED TO BE.I USED PLASTIC WASHERS UNDER THE SCREWS.

THREE TIME THEY TRIED TO FIX A NOISE AT THE LEFT DOOR GLASS,IT'S STILL THERE,NOW THEY REFUSE TO TRY AGAIN.

NO SATISFACTION FORM THIS DLR.

THANKS

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I HAVE THE SAME PROBLEM WITH MY 08 RX.PAID ALMOST 45K,THE DLR.SAID IT'S NORMAL FOR THE RX AND OTHERS TO SHIFT THAT WAY,BUT ,HE SAID, IF THEY DISCOVER A FIX FOR IT THEY WILL NOTIFY ME. I'M STUMPED. IF IT'S MORNAL, WHY WOULD THEY BE LOOKING FOR A FIX ? THE TRANS FEELS LIKE IT SLIPS AT A SLOW DOWN SPEED OF ABOUT 25-30 I CAN FEEL IT SHIFT OUT BY ITSELF,WHEN IT DOES I ACCELERATE AND CAN FEEL IT SLIP. DLR.CALLS IT A HESITATION CAUSED BY A FLY BY WIRE,SINCE 01. I THINK HE'S ON DRUGS.

BROUGHT IT BACK 3 TIMES FOR THIS PROBLEM.NOTHING WRONG THE 1ST. TIME.

2ND. TIME THE EASTERN REP CHECKED IT OUT AND SAID THERE IS NO POSSIBLE FIX FOR IT,WHEN THERE IS , THEY WILL CALL.

3RD. TIME THEY CANT DUPLICATE IT ( SOUNDS FUNNY TO ME )

85OOK LATER SAME PROBLEM.AND YES ROOF RACK RAILS ARE LOOSE,NOT DESIGNED TO BE.I USED PLASTIC WASHERS UNDER THE SCREWS.

THREE TIME THEY TRIED TO FIX A NOISE AT THE LEFT DOOR GLASS,IT'S STILL THERE,NOW THEY REFUSE TO TRY AGAIN.

NO SATISFACTION FORM THIS DLR.

THANKS

Puzzling, very....

There now seems to be two aspects of the Toyota and Lexus FWD and F/AWD product line that customers appear to be uncomfortable with, some to the point of considering at least one of these aspects to be a design flaw bordering on being unsafe to drive. The aspect owners seemingly consider unsafe would be the 1-2 second transaxle downshift delay/hesitation in certain instances about which lots have already been posted.

The latest complaint seems to involve the new firmware version which supports the newly implemented uphill/downhill shift pattern/schedule.

I don't have any problem with the uphill aspects, it is rather nice to have the transaxle automatically downshift, and hold the downshifted gear for a prolonged period, if I have enter an area of inclined roadbed. But I'm not altogether sure I understand the logic behind how the firmware decides that I need, want, engine braking when trying to slow going downhill.

It looks as if "daddy" has inadvertently encountered the downhill shift logic in a situation that would normally result in the upshift and delayed downshift situation.

Strange.

I have to wonder if the BA, Brake Assist, firmware is being "high-jacked" and now used to "trigger" the downhill shift, downshift, to "engage" engine compression braking.

Brake assist is supposed to provide extra braking power, HEAVY brake application, if it senses a panic braking situation. I presume it "watches" the rate at which the driver moves from the gas pedal, say partial depression, to braking. How quickly you go from "cruise" to braking.

That aspect I can understand and applaud.

But how does the engine/transaxle ECU control firmware decide that I want engine compression braking for speed restraint going downhill...??

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I HAVE THE SAME PROBLEM WITH MY 08 RX.PAID ALMOST 45K,THE DLR.SAID IT'S NORMAL FOR THE RX AND OTHERS TO SHIFT THAT WAY,BUT ,HE SAID, IF THEY DISCOVER A FIX FOR IT THEY WILL NOTIFY ME. I'M STUMPED. IF IT'S MORNAL, WHY WOULD THEY BE LOOKING FOR A FIX ? THE TRANS FEELS LIKE IT SLIPS AT A SLOW DOWN SPEED OF ABOUT 25-30 I CAN FEEL IT SHIFT OUT BY ITSELF,WHEN IT DOES I ACCELERATE AND CAN FEEL IT SLIP. DLR.CALLS IT A HESITATION CAUSED BY A FLY BY WIRE,SINCE 01. I THINK HE'S ON DRUGS.

BROUGHT IT BACK 3 TIMES FOR THIS PROBLEM.NOTHING WRONG THE 1ST. TIME.

2ND. TIME THE EASTERN REP CHECKED IT OUT AND SAID THERE IS NO POSSIBLE FIX FOR IT,WHEN THERE IS , THEY WILL CALL.

3RD. TIME THEY CANT DUPLICATE IT ( SOUNDS FUNNY TO ME )

85OOK LATER SAME PROBLEM.AND YES ROOF RACK RAILS ARE LOOSE,NOT DESIGNED TO BE.I USED PLASTIC WASHERS UNDER THE SCREWS.

THREE TIME THEY TRIED TO FIX A NOISE AT THE LEFT DOOR GLASS,IT'S STILL THERE,NOW THEY REFUSE TO TRY AGAIN.

NO SATISFACTION FORM THIS DLR.

THANKS

Puzzling, very....

There now seems to be two aspects of the Toyota and Lexus FWD and F/AWD product line that customers appear to be uncomfortable with, some to the point of considering at least one of these aspects to be a design flaw bordering on being unsafe to drive. The aspect owners seemingly consider unsafe would be the 1-2 second transaxle downshift delay/hesitation in certain instances about which lots have already been posted.

The latest complaint seems to involve the new firmware version which supports the newly implemented uphill/downhill shift pattern/schedule.

I don't have any problem with the uphill aspects, it is rather nice to have the transaxle automatically downshift, and hold the downshifted gear for a prolonged period, if I have enter an area of inclined roadbed. But I'm not altogether sure I understand the logic behind how the firmware decides that I need, want, engine braking when trying to slow going downhill.

It looks as if "daddy" has inadvertently encountered the downhill shift logic in a situation that would normally result in the upshift and delayed downshift situation.

Strange.

I have to wonder if the BA, Brake Assist, firmware is being "high-jacked" and now used to "trigger" the downhill shift, downshift, to "engage" engine compression braking.

Brake assist is supposed to provide extra braking power, HEAVY brake application, if it senses a panic braking situation. I presume it "watches" the rate at which the driver moves from the gas pedal, say partial depression, to braking. How quickly you go from "cruise" to braking.

That aspect I can understand and applaud.

But how does the engine/transaxle ECU control firmware decide that I want engine compression braking for speed restraint going downhill...??

The best way I can descibe the downshifting is how it feels when I drove a standard. Whe I had a standard I always with downshift for example when coming to a red light and let the engine compression slow/brake the car before I used the brakes. The RX seems to do this on its own and I have become use to it .

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As I already stated, Toyota has adopted a new shift procedure commonly referred to as "uphill/downhill shift logic". They imply that there is a unique procedure involving brake application that the driver must use to "invoke" this new feature. Or they may simply be "watching" the level of torque the engine must produce to attain, sustain, a reasonably high roadspeed and react accordingly if the driver applies braking.

The vehicle might essentially be coasting, very little engine torque required, and this may be used to trigger the new logic if/when the driver applies braking.

My best guess would be that if you do a long "coast" all the way up to a stop sign with light throttle applied and then apply the brakes the downhill logic will trigger. Obviously this would be more likely to occur if the stop is being made while traveling downhill.

On the other hand a period of coasting with no throttle opening at all would trigger the throttle fully closed upshift sequence at 40-30 MPH, or while slowing to a stop, OR NOT, at 10-0 MPH.

Apparently the "OR NOT" is one of the documented causes for the 1-2 second DBW enforced downshift delay/hesitation.

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  • 3 months later...

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