[voy1993]

2004 Sienna AWD XLE

I have been trying to understand why my Sienna gets poor mileage no matter how conservatively I drive. The low can be as low as 13 mpg when I am doing only short city trips, and the best has been ~ 22 on mostly highway trips up to the ski area.

I recently started watching the tach while driving to see where the torque converter lockup is engaging. As far as I can tell, it only locks up when cruising at speeds of 56 mph or over. At no time does it lock up below 56 mph. Since a large part of my driving is in the city, in the 35-55 mph range where getting rid of torque converter losses would make a big difference, I am trying to track down whether there is a problem with my sienna, or some way to get it to lockup at lower speeds.

Since my last fill up, I have been making a real effort to drive such that the lockup occurs in as much of my drive as possible, and had traffic allowing that on my trip yesterday to the mountain. I have seen as a result, about a 3 mph increase in mileage on the mpg avg the car gauge shows me. So I really would like to make the lockup work better at lower speeds.

I found this link from SiennaChat for this van which lists shift and lockup speeds:
https://www.siennachat.com/attachments/shifts-pdf.893/

It says that the lockup in 5th gear should occur at 40-44 mph, as opposed to the 56mph that I am seeing on my van. Surprisingly, the lockup speed for lower gears is higher, 65-68 mph for 4th, and 47 mph for 3rd gear. Or is this bad data? Lockup at lower speeds/gears would make great sense for mileage when climbing the long hill to the mountain.

If this is true, what would be likely causes for my van waiting till 56 mph before lockup. It could be the input speed sensor giving low readings, which would affect all the lockup speeds, which might also affect the shift speeds, but maybe the shift speeds are controlled by the output speed sensor. The shift speeds seem reasonable.

I have checked for codes, and found none. Trans fluid was flushed till clear red when I bought the van a couple years ago.

Any help learning more about possible reasons for the seeming lack of lower speed lockup would be appreciated.

 

[sixto]

Gas Mileage of 2004 Toyota Sienna says 16/22 so you’re not too far off. Skiing sounds like climbing so 22 is amazing. Have you confirmed the van is in top shape and not hindered by unnecessary weight, and drag from excessively wide tires, etc?

You might invest in a scanner with live data or even Techstream itself so you can monitor TC lock up status and pedal/throttle position more precisely than watching for a flicker on the tach.

Sixto
‘04 LE FWD 207K miles

 

[BillG]

13 in-town in the winter, is not totally unreasonable in cold areas. That said, you will need access to some live data to actually diagnose any potential problems or do some alternate detective work to try to find potential problems. I'd start with a new air filter, if yours is close to (or past) a year old. Make sure oil and transmission fluids look good and are at their proper "full" level and check the coolant level to make sure it's totally full. Next, I would do a visual inspection of all the vacuum lines to make sure they're all present and not cracked/split. Next up would be to spray a highly flammable spray like starter fluid to fog the gasket areas while listening to the RPM to check for TB or intake vacuum leaks. Lastly, since you're just giving everything a checkup, make sure the battery terminals are clean amd tight. Then, take the car for a spin to the nearest parts store and ask them to check the battery and alternator. You could do some other things like cleaning the MAF and wiping down the TB with a rag soaked in carb/TB cleaner.

Aside from those things, that's about all you can do without data, unless you want to start making educated guesses. For instance, when was the last time the plugs were changed? How about the timing belt? What is the condition of your tires and what PSI are they? Any chance your exhaust has problems and may be restricted? Etc. Basically, you need to ask/investigate any and every possible cause of reduced mileage to rule them out.

 

[voy1993]

Gas Mileage of 2004 Toyota Sienna says 16/22 so you’re not too far off. Skiing sounds like climbing so 22 is amazing. Have you confirmed the van is on top shape and not hindered by unnecessary weight, and drag from excessively wide tires, etc.

You might invest in a scanner with live data or even Techstream itself so you can monitor TC lock up status and pedal/throttle position more precisely than watching for a flicker on the tach.

Sixto
‘04 LE FWD 207K miles

Maintenance is all up to date. All fluids were completely replaced when I got it 2 years ago. I have the techstream version that came with my OBD-usb connector, but cannot pay a lot of attention to it while driving. The lockup is pretty obvious on the tach - RPM drops for a second, then locks to the speed I am going. There is a very clear lower boundary at which it locks - 56 mph. below that, no lockup. according to the documentation on the U151f transmission, that should be 39-43 mph. Toyota Sienna Service Manual: U151f automatic transaxle - Service specifications
After my latest experiments with speeding up my driving to force lockup and getting substantial improvement in mileage by doing so, my focus here is to find out why my Sienna will not lockup according to the specs for it, as that would clearly improve gas consumption. Or maybe someone with a similar vehicle could tell me that they see the same (or different) lockup speeds. If someone else with a 2004 Sienna shows lockup working around 40 mph, that would tell me that something is likely wrong with mine.

 

[cougarhound]

Checking tire pressure is so underrated for mpg. I like to run them at 35-40psi over factory spec.

 

[voy1993]

Checking tire pressure is so underrated for mpg. I like to run them at 35-40psi over factory spec.

I have tires at 37 psi. I do hope you don't really mean 35-40 psi higher than the spec.

 

[voy1993]

13 in-town in the winter, is not totally unreasonable in cold areas. That said, you will need access to some live data to actually diagnose any potential problems or do some alternate detective work to try to find potential problems. I'd start with a new air filter, if yours is close to (or past) a year old. Make sure oil and transmission fluids look good and are at their proper "full" level and check the coolant level to make sure it's totally full. Next, I would do a visual inspection of all the vacuum lines to make sure they're all present and not cracked/split. Next up would be to spray a highly flammable spray like starter fluid to fog the gasket areas while listening to the RPM to check for TB or intake vacuum leaks. Lastly, since you're just giving everything a checkup, make sure the battery terminals are clean amd tight. Then, take the car for a spin to the nearest parts store and ask them to check the battery and alternator. You could do some other things like cleaning the MAF and wiping down the TB with a rag soaked in carb/TB cleaner.

Aside from those things, that's about all you can do without data, unless you want to start making educated guesses. For instance, when was the last time the plugs were changed? How about the timing belt? What is the condition of your tires and what PSI are they? Any chance your exhaust has problems and may be restricted? Etc. Basically, you need to ask/investigate any and every possible cause of reduced mileage to rule them out.

Plugs changed last summer. Tires have maybe 12,000 miles on them, at 37psi. Battery 3 months old. Brakes shoes recently replaced and calipers cleaned and lubed. Parking brakes adjusted for minumum drag.
I am really focused on the T.C. lockup because it seems out of spec at 56 mph minimum operation. Any chance you could try yours an let me know the minimum speed it will lockup. The spec for the tranny has it around 40 mph. If you have a tach in your Sienna, when it locks up, the rpm will drop a few hundred rpm, then settle, and then not vary with minor throttle changes like it does without lockup.

 

[3Wheelerguy]

Lock up is controlled by the ECU. In the link you posted it shows that lock up is with 5% throttle opening.' IF' load and opening is more. I do think lock up will not happen.
AWD are not known for great gas mileage.

 

[cougarhound]

I have tires at 37 psi. I do hope you don't really mean 35-40 psi higher than the spec.

Nope 37 sounds good. As the guy in the video says, I would think it would be pretty obvious if the torque converter was not locking up.

 

[sixto]

That’s a good point - there might be a load parameter preventing lock-up but below CEL threshold. Use live data to monitor load through airflow, throttle position and fuel trims, then compare with other AWD vans.

Wheel bearings are good? No dragging brakes?

Sixto
‘04 LE FWD 207K miles

 

[ericreyn]

Fwiw i was watching the shifting behavior of my 2009. It won't even shift into the final gear til maybe 50 or so. After in the final gear it does seem to "lock" , I don't think this happens in lesser gears. And yea AWD,S are not known for any fuel economy benchmarks. Your milage sounds in the ballpark.

 

[sixto]

Does the TC only lock up in 5th gear?

I have another car that can lock the TC in 2nd through 5th. Also has partial and full lockup capability. Not bragging, just wondering if Toyotas have the same capability.

Sixto
‘04 LE FWD 207K miles

 

[bencahill]

I'm not sure if the shift logic is different in the 2007-2010 with the 3.5L, but my 2009 goes into its lowest RPM right around 45mph. I am guessing it is TC lockup. I can go from there to 70mph without any more shift/RPM changes, and at 70mph it is right at 2000 RPMs. I don't remember the RPMs at 45mph, but probably around 1300.

 

[cougarhound]

My 4runner doesn't shift when it is cold. It's pretty obvious when it does that. High rpms. I don't know why they design it like that though. The video I linked explains what checks the ecu goes through before it enables lockup. One of those checks is the engine temp.

 

[sixto]

Lots of cars hold lower gears when cold to get the cats up to temp more quickly.

Sixto
‘04 LE FWD 207K miles

 

[ericreyn]

I'm not sure if the shift logic is different in the 2007-2010 with the 3.5L, but my 2009 goes into its lowest RPM right around 45mph. I am guessing it is TC lockup. I can go from there to 70mph without any more shift/RPM changes, and at 70mph it is right at 2000 RPMs. I don't remember the RPMs at 45mph, but probably around 1300.

After further attention I agree with this. It needs to be at least 45 for this to happen. At 40 it won't go into the highest gear and it don't seem to lock either until the final gear.

 

[bencahill]

After further attention I agree with this. It needs to be at least 45 for this to happen. At 40 it won't go into the highest gear and it don't seem to lock either until the final gear.

Ah yes, you're right, when I hit 45, it has two RPM drops to get to the lowest RPM. I assume they are 1) shifting to highest gear, and then 2) torque converter lockup.

I should watch PIDs on my OBDLink MX+ some time when driving to understand more about the shifting. That should confirm whether or not the torque converter will lock up in lower gears.

 

[voy1993]

2004 Sienna AWD XLE

I have been trying to understand why my Sienna gets poor mileage no matter how conservatively I drive. The low can be as low as 13 mpg when I am doing only short city trips, and the best has been ~ 22 on mostly highway trips up to the ski area.

I recently started watching the tach while driving to see where the torque converter lockup is engaging. As far as I can tell, it only locks up when cruising at speeds of 56 mph or over. At no time does it lock up below 56 mph. Since a large part of my driving is in the city, in the 35-55 mph range where getting rid of torque converter losses would make a big difference, I am trying to track down whether there is a problem with my sienna, or some way to get it to lockup at lower speeds.

Since my last fill up, I have been making a real effort to drive such that the lockup occurs in as much of my drive as possible, and had traffic allowing that on my trip yesterday to the mountain. I have seen as a result, about a 3 mph increase in mileage on the mpg avg the car gauge shows me. So I really would like to make the lockup work better at lower speeds.

I found this link from SiennaChat for this van which lists shift and lockup speeds:
https://www.siennachat.com/attachments/shifts-pdf.893/

It says that the lockup in 5th gear should occur at 40-44 mph, as opposed to the 56mph that I am seeing on my van. Surprisingly, the lockup speed for lower gears is higher, 65-68 mph for 4th, and 47 mph for 3rd gear. Or is this bad data? Lockup at lower speeds/gears would make great sense for mileage when climbing the long hill to the mountain.

If this is true, what would be likely causes for my van waiting till 56 mph before lockup. It could be the input speed sensor giving low readings, which would affect all the lockup speeds, which might also affect the shift speeds, but maybe the shift speeds are controlled by the output speed sensor. The shift speeds seem reasonable.

I have checked for codes, and found none. Trans fluid was flushed till clear red when I bought the van a couple years ago.

Any help learning more about possible reasons for the seeming lack of lower speed lockup would be appreciated.

I seem to have jumped to a conclusion in this post that because I am getting higher "avg MPG" readings by changing my driving habits to get more lockup time. Indeed, the reported mpg went up by a couple of mpg. However, today I filled up again after 2 trips up to the ski area, and actually got an slightly lower calculated mpg from miles driver divided by gas refilled gallons. The mpg "gauge" showed 25.6 which is a couple mpg higher than recent previous results, however, real mpg turned out to be 21.426 mpg. So it appears that driving to maintain T.C. lockup might have just fooled the vans calculation, making it read even higher than it did with my previous driving. It has always read 2-3 mph high previously. The actually mpg could even have been reduced it bit. Or, this could be a fill up nozzle shut off difference.

I still want to do some more checks of the lockup and it's influences sometime when I can arrange for someone else to drive while I watch the data from the engine.

Thank you everyone for your helpful comments.

 

[cougarhound]

I seem to have jumped to a conclusion in this post that because I am getting higher "avg MPG" readings by changing my driving habits to get more lockup time. Indeed, the reported mpg went up by a couple of mpg. However, today I filled up again after 2 trips up to the ski area, and actually got an slightly lower calculated mpg from miles driver divided by gas refilled gallons. The mpg "gauge" showed 25.6 which is a couple mpg higher than recent previous results, however, real mpg turned out to be 21.426 mpg. So it appears that driving to maintain T.C. lockup might have just fooled the vans calculation, making it read even higher than it did with my previous driving. It has always read 2-3 mph high previously. The actually mpg could even have been reduced it bit. Or, this could be a fill up nozzle shut off difference.

I still want to do some more checks of the lockup and it's influences sometime when I can arrange for someone else to drive while I watch the data from the engine.

Thank you everyone for your helpful comments.

I'm not sure what kinda mpg you're expecting. I expect Sienna will get no better than 20mpg combined. A Honda CR-V gets about 25mpg. Just the nature of the beast. Are your drum brakes dragging? Touch the wheel after you drive. Make sure it's not hot.

 

[Tripper]

People complain about EVs loosing range in cold weather, guess what ICE Vs also loose range in cold weather! Your MPG seems to be in the correct ball park already.