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Discussion Starter · #1 ·
Hello all -

Hoping I could get some help on an issue I'm having with my Sienna. I recently got a transmission flush (along with a tuneup on this trip) and everything seemed to be perfectly fine - I just hit 100,000 miles. I then headed back home from visiting family (~12hr+) and my check engine light came on (going highway speeds) along with the traction control alert and the other alert (forget what it is). I stopped to get gas and my mechanic thought it was the gas cap and suggested that I buy a new gas cap. No worries, so I kept driving. After driving about 15 more minutes, my car's transmission was knocking and was super jerky and felt like someone was hitting the back of my van multiple times.

To remedy this, I reset the battery so that the check engine light (CEL) wouldn't appear and it seemed to have fixed this. However, every hour it showed up and every hour I just kept unhooking the battery just so that I could make it home. Long story short, I finally made it home and took the car to Toyota and they said that they couldn't help me because they couldn't find the error code because I cleared the memory from resetting the battery and they drove the car and felt there were no issues. It's been a few weeks now (I've driven the car no longer than 1.5hr straight) and the check engine light came on after I drove the van ~1hr from visiting friends. We were close enough to home that I didn't need to reset the battery and made it without any crazy jerking or shifting issues. After about 4 hours of leaving the car idle, I went back and the CEL is no longer present. I still have plans on taking it to the dealership again to hope to get it remedied (they should have the code now), but was wondering if anyone has any thoughts on why this would be happening and would a transmission drain/fill or another flush would fix this. It's possible that the mechanic may have under or overfilled the fluids?

Apologies for the novel, but wanted to provide the whole story. Thanks in advance.
 

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Hello, sorry to hear of your transmission problems. There are a few things you can check or have the dealer check. But first, I know this is too late already but never ever flush a transmission. Always do a drain and fill. There has been many many instances where flushing the transmission has resulted in its untimely death. But since your has been flushed I would first verify the correct level of trans fluid is in the vehicle. This can easily be done via the following procedure or you can have the dealer verify the level.

To check Fluid level:
  • You will need a way to measure the temp of the trans fluid (I use and ODB reader to do this)
  • You will need a 6mm hex wrench
  • You will need a pan to catch fluid.
  • Van needs to be at a level surface, not at an incline driveway.
  • In the morning, when your trans is cold, start the car and let it idle and monitor the transmission fluid temp.
  • Once the trans fluid temp is at 110F, do the following steps quickly before the trans fluid goes above 114F,
  • Keep the engine running, do not turn off the engine
  • Unscrew the trans fluid drain bolt (6mm hex) to drain the fluid.
  • Only unscrew the drain bolt, do not unscrew and remove the plastic straw that is inside the pan after you remove the drain bolt.
    • If there is no fluid that comes out, then your transmission is underfilled.
    • If there is fluid that comes out in a steady stream for a bit and then the stream gurgles, then your transmission is overfilled.
    • If there is some fluid that comes out, but not a steady stream but rather just a bit or is gurgling out, then your fluid level is correct.
  • If you are uncomfortable or unsure if you can do this process, have the dealer check the fluid level for you.

Another thing to ask your trans flush place is what kind of fluid did they do the flush with? Toyota trans are picky about fluid and it is recommended to use only Toyota WS fluid.
But either way, when the issue happens again, I would think the best bet is to take it to dealer to diagnose.

Again, sorry to hear of your trans issue and hopefully it is not something major and can be remedied easily.
 

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I doubt it's a transmission issue. Sounds like some sensor somewhere is timing out and causing a driveability problem. When you reset it, it takes a while to come back. If it was a bad transmission you wouldn't be getting that proper operation before it decided it needed to act up again.
 

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The easy button here is to get yourself an OBD-II dongle ($6-25) to match what ever smartphone you have. For Android get a BT adaptor. For iPhone get a Wifi adaptor. Then you'll need an app. For Android get Torque (either the free version or the $5 PRO version). For iPhone there are a number of apps, I just haven't found the one I like for the Sienna yet because I use my Android 11 tablet and Torque. This will let YOU read and clear the codes without having to disconnect the battery (Winter is coming!). Even if there is no CEL showing you may have pending codes or historical codes that can be read. Once the problem happens again, read the code, do a screen grab and show that to the dealer.
 

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You will need a way to measure the temp of the trans fluid (I use and ODB reader to do this)
The van has this built in. You can shift back and forth between N and D rapidly multiple times, and then this puts the car shifter display into a transmission temp indicator. When no gear is indicated, the trans fluid is too cold. When D appears, trans fluid is at the right temp for the overflow tube draining. When D flashes, trans temp is too hot. Car is in park this entire time, but again, just using the shift indicator as a temp gauge.

If you're curious I can get the exact procedure from the FSM I have downloaded at home, but don't have that here now. It lists the specific number of shifts within a specific timeframe. The following link just says "do it rapidly" Transmission Fluid Change - Drain when oil cold or warm...
 

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The van has this built in. You can shift back and forth between N and D rapidly multiple times, and then this puts the car shifter display into a transmission temp indicator. When no gear is indicated, the trans fluid is too cold. When D appears, trans fluid is at the right temp for the overflow tube draining. When D flashes, trans temp is too hot. Car is in park this entire time, but again, just using the shift indicator as a temp gauge.

If you're curious I can get the exact procedure from the FSM I have downloaded at home, but don't have that here now. It lists the specific number of shifts within a specific timeframe. The following link just says "do it rapidly" Transmission Fluid Change - Drain when oil cold or warm...
In order to put it in Trans temp mode, you need to short 2 jumpers in the ODB connector. Forgot specifically which ones, but the jumpers have to be shorted first before it will go into trans temp monitor mode.
 

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In order to put it in Trans temp mode, you need to short 2 jumpers in the ODB connector. Forgot specifically which ones, but the jumpers have to be shorted first before it will go into trans temp monitor mode.
Hmm, thanks. I reviewed my FSM, and there's a key point they emphase that neither of us mentioned. And that is engine idle speed control mode. They say the following for using Techstream:
NOTICE: Be sure that terminals TC and TE1 are not connected. If the terminals are connected, the fluid level cannot
be precisely adjusted due to fluctuations in engine speed.

HINT:
  • Disconnecting terminals TC and TE1 activates the engine idle speed control mode.
  • In the engine idle speed control mode, engine idle speed control starts when the fluid temperature becomes 35°C (95°F) or more and the engine speed is maintained at approximately 800 rpm.
  • Even after terminals TC and TE1 are disconnected, the fluid temperature detection mode is active until the ignition switch off.
Terminals TC and TE1 are connected and disconnected using Techstream.

And for not using Techstream they say:
NOTICE:
Be sure that terminals TC and CG are not connected. If the terminals are connected, the fluid level cannot
be precisely adjusted due to fluctuations in engine speed.

HINT:
  • Disconnecting terminals TC and CG activates the engine idle control mode.
  • In the engine idle speed control mode, engine idle speed control starts when the fluid temperature becomes 35°C (95°F) or more and the engine speed is maintained at approximately 800 rpm.
  • Even after terminals TC and CG are disconnected, the fluid temperature detection mode is active until the ignition switch is turned off.
In this case, terminals TC and CG are pins 13 and 4, respectively, of the OBD connector.
Rectangle Font Parallel Slope Pattern


The non-Techstream procedure is:
  1. Connect pins 4 & 13 of OBD connector.
  2. Depress brake pedal and start engine.
  3. Slowly move shift lever from P to D, then back to P (slowly, to circulate the fluid through each part of the transmission.
  4. While watching gearshift indicator, move shift lever from D to N and back at 1.5 second intervals for 6 seconds or more. This will cause vehicle to enter fluid temp detection mode.
  5. Check that the D shift indicator comes on for 2 seconds.
  6. Move shift lever from N to P.
  7. Release brake pedal.
  8. Remove jumper from OBD connector. Removing jumper activates engine idle speed control
  9. Allow engine to idle until the D shift indicator comes on again
    1. Below temp the D indicator is off
    2. At temp (104 to 113 °F) the D indicator is on
    3. Above temp the D indicator is blinking
  10. Remove the overflow plug
  11. If fluid overflows
    1. Wait until fluid slows and only drips come out
    2. Remove fluid fill plug
  12. If fluid does not overflow
    1. Remove fluid fill plug
    2. Add fluid through refill until fluid comes out of the overflow plug hole
    3. Wait until fluid slows and only drips come out
  13. Install overflow plug
  14. Install refill plug
  15. Turn off engine
EDIT: Oct 3rd, 2022. I didn't include the steps for what to do if fluid doesn't come out when you remove the overflow plug. Added for future clarity. I originally ignored this since every post I've seen here about trans fluid changes talks about slighly overfilling after a drain, but that wasn't covered in this thread and so including here in case someone finds this in the future and thinks it's cool if nothing comes out when the plug is removed, and hasn't seen the other posts about a slight (~0.5 quart) overfill when refilling after a drain. Changes are in bold. My apologies for not including this originally.

In both cases, using Techstream and not, they tell you to make sure AC, audio system and lighting systems are off. And in both cases, they have you activate idle speed control, to stabilize engine speed and hold it at 800 RPM. They seem very persistent that if this is not activated, that you cannot set the transmission fluid level correctly. In both cases, they still have you move the shift lever from N to D and back at an interval of 1.5 seconds for 6 seconds or more, at which point the transmission indicator becomes the temp indicator. Though in the case of the Techstream, you are viewing live transmission temps too, so you don't really need this.

In summary: You are correct, if you don't jumper pins 4 & 13 of the OBD connector, moving the shift lever from N to D multiple times won't bring up the temp indicator using the gearshifter. More importantly though, jumpering pins 4 & 13, then removing the jumper, activates engine idle speed control, which they say is required to get the transmission fluid to the correct level. So, to do this properly, you need to jumper pins 4 & 13 of the OBD connector, then remove the jumper, even if using an OBD reader to monitor transmission temps. So at that point, may as well just use the gearshift display to get the correct trans temp.
 

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Discussion Starter · #9 ·
Very thankful for everyone's responses! I did finally get the Check Engine Light (CEL) to display again and was able to make it home. The next day, I took the car to my friend's place. Oddly, the CEL disappeared the next day. Luckily the code was still in memory and it produced a 'P0712 Transmission Fluid Temperature Sensor A Circuit Low' response. Took the van to the dealership and they are trying to keep the car for 2 days to reproduce, but I told them that they most likely can't unless they drive 70mph+ for 1.5hrs+. They were thinking that it was a transmission issue, but I asked if it's the transmission, how am I able to reset the battery and keep going another hour. He then recommended that I replace the temperature sensor and if that doesn't resolve the issue, replace the transmission ECU (think that's what he recommended?) - cost being ~$1700 and $1600 respectively. Thought I wouldn't have to do major service to the car until wayyyy down the road, but kind of at a crossroads. I heard that replacing the transmission temp sensor is very labor intensive and many tech's can make mistakes which can lead to more issues with the car.

Spending at least $1700, potentially $3300...I have people telling me to trade the car in and others saying to just replace the sensor. What would you do? Appreciate any input and grateful for those who have already assisted.
 

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If I had a transmission issue, I believe I would locate a well-reviewed independent transmission shop in my area and take my van there. I feel like a good transmission shop will be better than a dealer at fixing transmission issues, since that is most or all the work they do on vehicles, and almost certainly much cheaper.
 
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