Multiple Speedometer Issues

Hello. I’m new here and have a question regarding a really annoying situation I have. I have a 2021 Tundra Double Cab SR5 2WD. Since I took the truck off the lot I noticed that the speedometer did not match the digital speed reading being about 1mph off, and the digital reading did not match the cruise control set speed, too. I asked the technician at the dealership about it and he said unless it’s 2-3mph off then they don’t do anything about it. Okay, that didn’t make much sense but okay. I recently noticed while passing some roadside radar signs that they are indicating my speed as being 2-4mph slower than what my speedometer is showing. Realizing that my not be real accurate I downloaded an app that would show me my speed, and the app confirmed what the radar signs were telling. I went to Toyota to ask them about that and to see about getting that corrected since it’s still under warranty, even showing them a picture of what my dash was showing when all three speeds on the dash did not match. Guess what they told me? They tried to tell me that the lower speed on the digital readout was showing the truck was accelerating to the set speed for the cruise control, and that is why the speedometer was showing faster than the cruise setting, even though I told them that I was cruising and those numbers were not changing. They further told me they wouldn’t be able to make any changes, but if I wanted them to they could run a diagnostic on it even though they would not be able to fix it. I asked them if the sensor could just be bad and they didn’t want to entertain that thought, telling me that if there was an issue the radar for the cruise control would not work and I would get a warning regarding that. UGH!!! BTW, I’m running factory tire sizes so it’s not an issue of having different size tires.

Any thoughts or ideas about this? I’m wondering if I could change the sensor myself, but I can’t figure out which speed sensor to replace or where it’s located, and if in changing it that fixes the issue, what are my chances they would pay me back for it?

 

The physical needle I would say is a manufacturing tolerance issue and most likely can't be fixed without pulling the gauge apart/replacing it. The digital read outs not being the same is very weird, but I doubt there is anything they can do besides physically replace the gauge cluster since they probably don't have access or the engineering knowledge to fix whatever the software issue is.

I'm not a EE but I'd guess the two data points are pulling data from different sensors or something where there is a slight deviation or rounding error. So they're not wrong, just not identically matched up for whatever reason.

 

Set your display to MPG instead. There fixed.

 

My 2021 SR5 TRD OR does the EXACT same thing. All 3 issues the same as yours.

 

My 2020 does the same occasionally with the cruise and actual speed being one off. I assumed the two readouts just round to the closest whole numbers and the cruise may have been set somewhere in the middle of the 2 numbers, like 64.5 mph in your example.

 

I haven’t noticed this on my 2020. The middle display is usually on audio though so I need to double check.

For your last question, if you have a Platinum warranty plan it says the Speedometer is covered. However, I don’t see anything specific to speed sensors.

 

Wow! Surprised so many people are having the same issue. You would think all the indicators are getting their signal from the same sensor so they would match, but maybe there’s more to this issue than that. I would think there should be a fix for it, but if not maybe someone can come up with one.

Thanks everyone for the replies and input. Greatly appreciated.

 

My 2020 does it.

My wife's 2016 Accord does it.

It's such a small tolerance that I ignore it.

 

Yep, my 2021 does the same thing. My 2017 also did the same thing. My wife's 4Runner also does it.
It is annoying, you'd think they would always be in sync with each other.
On the other hand I never had this issue with my '69 Corona

 

The quick answer is Toyota got lazy and is operating inside "acceptable" ranges. Unfortunately nothing is wrong with your truck and it is functioning "properly" no bad sensors ect.

To understand your problems you need to understand how the system works. Each wheel and tire combo has a wheel speed sensor that monitors wheel revolution speed with a "counter". The faster the counter is incrementing up, the faster the wheel is rotating. This is a basic explanation. Anyway the ABS ecu reads in the signals from all 4 wheel speed sensors and processes them. It then generates a signal to the instrument cluster to run the speedometer. This one signal runs both the digital screen and needle speedometer meaning they should always be the same, assuming your needle is initialized at 0 exactly. The needle is just a stepper motor and the speed signal tells it how far to rotate, if its not starting a perfect 0 it could be off by 1-2mph. This is the best explanation for this.

The cruise set speed actually comes from the Engine ECU and is a lower resolution speed signal compared to the one driving the speedometer. It stores it as it needs to know the set target speed so it can accelerate or coast the vehicle ect. It is close but sometimes not perfect.

Two reasons why error is introduced to the system.

1) Rounding error. The native format for all the speed signals is in Kmh and they are all converted to Mpg signals at the last step if Mph is the preferred unit in the truck. During this conversion you get some rounding error however it is minimal. I have seen cruise set at "70" but digital speed is "69", they are both rounded speeds due to the conversion.

2) The biggest issue is generic/universal parts. Toyota offers 4 different tire sizes for Tundra's which could be a problem. With 4 different tire sizes, you need 4 different ABS ecus as each of which is hard coded with a value that represents number of tire revolutions per mile. Toyotas answer, use one generic ABS ecu for all trucks with a generic value to represent tire revolution per mile. They can use the same computer on all trucks and be within a few percent error tolerance. This is why yours is off 2-4 Mph vs GPS. Had Toyota programmed a specific value for the exact tire size of each truck they would all be more accurate.

Someone pointed out all 2007+ trucks basically have the same ABS ecu part number, proof Toyota is just using generalized values that are close enough for 90% of owners/drivers.

 

As far as cruise control goes, I have yet to find a vehicle across any brand that perfectly maintains the set speed. Staying within 1 mph of the set point is pretty good given cruise control has to respond to a variety of factors going solely off the readings of one sensor. The car can't predict hills, wind, or anything else, so having a stick +/- 1 mph reduces the likelihood that the throttle will surge.

Tire size is a good point, besides tire wear, the OD of new tire will vary from brand to brand in the same size.

 

Sorry but this is not correct, the "vehicle speed sensor" in the transmission is for monitoring the front and rear transmission shaft rotation speed. This data is feed back to the Engine ECU to allow it to control transmission shifting. The tundra does not have a separate Transmission ECU, all transmission functions are controlled by the engine ECU and the two speed sensors in the transmission only feed data into the engine ECU for transmission control.

The Speedometer and Odometer both definitely do work off the ABS wheel speed sensors. I have logged the CAN data from them and the ABS ecu many many times. Look at this info I copied from the Tundra repair manual. It clearly says the Speedometer input is a signal received from wheel speed sensors and sent to the instrument cluster by the Skid Control ECU (ABS Ecu). You will notice the all 4 wheel speed sensors and the Speedometer also operate on the same range of values 0-202 Mph

The system works the way I described above and the ABS ecus are generic to fit all factory tire sizes.

 

They're allowed to read high by quite a lot. My Tacoma would have needed the needle on 71 mph to be driving at 64 mph actual with factory tires and gears. I think it was something to do with the R155 used in both the 5 lugger and 6 lugger trucks.

 

No apology needed, I stand corrected. Thanks for the info, I didn't realize Toyota was doing it that way on these trucks. The older LandCruisers kept the speedo/trans on one sensor and only used wheel speed sensors for ABS/ATRAC. Thanks for setting me straight.

 

So, if I want my speedometer to be more accurate instead of being off 2-4 mph, what would I need to do to adjust or calibrate it? Just a side note, I even checked the odometer against the mile marker signs in the side of the highway and it shows it’s off.

Thanks again for all the input and information. Much appreciated!

 

My 21 does the same thing. However I was thinking mine was off due to my VIN specifying 18” wheels but the wheels were changed to 20” at port or dealer because of the TSS off road package.

 

Read your speed in KMH and program your specific tire size values into your ABS ECU

 

Recently purchased a 2021 1794 Tundra and discovered that the Digital display reads about 4-5 mph higher than the speedometer needle. Not sure which one to refer to when encountering "speed cops." Any suggestions?

 

download a speedometer app on your phone or use Waze and compare. Are you on factory tire size?

 

The car has a quite accurate speed reading. This is the work of toyota attorneys. The ecu takes the actual speed and adds a set %age increase for the display. Toyota doesn’t want to be named in a lawsuit involving speeding tickets so they add a provable buffer to protect themselves. Haven’t seen a car in the last 20 years that didn’t do this.

 

I’m curious your source on this. Adding an increase seems like it would set a manufacturer up for a lawsuit, not protect them.

 

Adding to the reported speed on the instrument makes it appear you are going faster than you are. Therefore if the speedo shows you going 40 MPH, you are actually going 37. The net effect is that you are driving slower, NOT faster than you think you are. Most bump it somewhere between 5-10%. As dicsussed above, this is easy to see. The ECU speed is easy to grab from your scan tool. You can observe that speed and then cross check the speedo, which is fed by the ECU, and see that it is higher. You can also observe that addition is not in MPH, but instead a percentage of the actual speed.

Sorry, but don't have a source for this. Just know they all do it. Some of this is just margin. if you put on larger tires or severely over inflate them, this reduces the speedo reading. Having a built in margin prevents you from blaming the manufacturer for not complying with speedo limits.

 

Tundras with stock 32inch tires go slower than the speedo.

Tundras with 33 inch tires are just about dead on correct match speed.