Transmission Temperature Gauge Range of Operation

I decided to create this to give you guys some feedback on the operational range of the transmission temperature gauge in the 07-13 trucks.

I have know the location of the trans temp data on the CAN bus for a while. I found the address as I was reverse engineering the cluster and was able to control the trans temp gauge by sending hex data to it from my laptop.

I finally got serious about understanding the math and conversion. The truck (like everything else automotive) reports the data in Celsius. Once I was able to scale it from CAN hex to C it’s a simple conversion to F. I ran Techstream watching the AT2 transmission temperature (the one that runs the gauge) from the engine ecu while running my CAN data logger also and printing a digital trans temp in F. All of my readings were within 0.10 degrees of what Techstream was reporting in F. Slight error induced when native format is C and Techstream as well as my logger were converting to F.

Long story short I was able to “map” the needle movements of the transmission temp gauge in my bench cluster.

Gauge start to read (pointing right at the C for cold) at about 100F

There is a large dead zone in the middle where the gauge is straight up and down from about 150F-270F

The needle doesn’t start moving again to hot until I send over 270F to the cluster.

All the way H hot where the red zone starts is 300F. I assume this is also when the AT oil temp light comes on but I don’t know that for sure. I didn’t log the indicator light signal.

Long story short if your trans temp needle every starts moving past halfway you are pushing 270F and it’s getting hot! (Obviously)

Here in Texas it’s 65ish degrees F outside and my drive around the neighborhood logging data my transmission was running 170-180F with no factory trans cooler. Verified by Techstream and my data logger.

On a day when it’s 100F + I will log it also for fun.

Side note a digital readout LCD showing exact transmission temperature can now easily be made so you can always know the current temp. This would be similar to the OBD gauges like Scan Gauge, Torque, OBD Fusion except it would not have to ask for the data using OBD commands. It would read direct from the ECU as it drives the needle on the cluster. In my experience the truck reports this data even if you don’t have a factory trans temp gauge on the cluster. More testing would verify that 100%

 

All of you guys with scan gauge or OBD gauges AND the factory trans temp needle gauge feel free to report if you see similar output. I am confident you should be.

 

Other transmission stuff.

Current gear 1-6 can be logged and displayed digitally as well as (NT) Transmission Input Shaft Speed. (This is generally very similar to engine/crank rpm)

I am also 99% torque converter lockup data is reported on the CAN.

 

Awesome as usual!

I’m monitoring trans temps in my radio with Maestro.

 

do you know if there are any X Gauge codes for the scangauge to report what gear the transmission is in? (I know this isn't quite what you are getting at, but couldn't find the X codes anywhere else)

 

Im not as familiar with the X gauge or know exactly what it is vs a regular scangauge.

However, I don’t know the code but could figure it out with some time logging. All the OBD2 stuff uses data request and has the answer returned. They ask a specific ecu a question using a read by identifier service and the identifier changes based on what parameter you are trying to read.

This works but gets slow refresh rates when you start asking for 20-30 things at once as it can only update them by asking for each one at a time.

It’s the same way Techstream reads live data from the truck as your drive.

Anyway using Techstream and my data logger I could figure out the request, response, and translation for current gear. Then just have to input that into scangauge in there format and it should work.

Truck defaults to 1 even when in PRN ect, once you put it in D and it shifts it will count up from 1-6, but base is 1 not 0

 

OBD Fusion here. Lockup (0/1) status is available.
The difference between RPM and the turbin RPM when in lockup is concerning when watch the gap widen. It doesn't seem to be an issue though!

Sadly I lost boost right as this screen shot was taken!

 

Is speed NO the rear transmission speed sensor? IE driveshaft rotation speed? Or is it somthing else?

 

Do you know if Maestro will display torque converter lockup status?

 

Yes, it's the output shaft speed.

The ECM is constantly comparing the turbin input shaft speed to the output shaft speed for the gear selected to verify the delta (slippage) is acceptable. When its not, it throws a code typically pointed at the solenoids responsible for making that gear selection as they were given a command. All the ECU knows is the command wasn't followed through. But all it can do is point at the messengers (solenoids).

 

X gauages are the programable gauges for scan gauge… I’ll have to poke into Techstream and my snap on scanner

 

Jeff, to your point, if the trans or engine coolant temp swung everywhere people would freak out. That's cool work talking on the bus and making things work. What grabbed your attention to make you look that deep?

Any chance you can poke around with the oil pressure gauge? It appears to be on CANH/CANL bus as best I can tell. I say this as I have two schematics and one shows pin 11 of the combination meter as oil pressure but that might be an input for the idiot light? IDK

I haven't done it on the truck but on the IS-350 I did a far less scientific approach took photos of the gauge and screen shots of Fusion while the engine came to temp. Roughly from 165F to 208F it's stable never moving, parked in the dead-band area.

What I find funny is why they don't dedicate a MAP area for the dang fuel tank? They could make it very accurate using the sensor and lookup map...

Nice work btw!

 

Oh yea in that case this can easily be done. Need a little bit of time logging data is all. I can probably do it for you if really want and I find the time.

 

I knew the transmission has a forward and rear speed sensor to measure mainshaft rpm. Seems the forward data is the only on that is "broadcast" out by the ECUs as I see no data that would be close to being the rear sensor on the bus.

Obviously you can get data from the rear senor via request and response from OBD protocol.

Alot of people make the mistake of assuming these speed sensors are for running the speedometer and don't understand the wheel speed sensors and abs ecu handles all of this instead.

Yes, I was not surprised to see a "large" dead zone in the gauge as normal temp can really vary and Toyota wants the gauge to look "normal" pointing straight up for all "normal" temps.

The wire is actually to run the oil pressure gauge. It runs off an analog resistance value from the oil pressure sender. Very similar to how the fuel level gauge works. There is no specific CAN messages that control the Oil pressure gauge like most the other ones (Techstream does have a diagnostic message to set the gauge ot 0% 25% 50% 75% 100% just to check it sill functions). Operational movement is determined by RPM and the resistance on the sender wire coming into the back of the cluster. I have looked and looked around the entire bus and I can see no data that would be close to the oil pressure values.

I got real interested in swapping gauge clusters so that opened up the world of CAN bus. Since then it has been more and more logging and learning. I have basically reversed the entire 07-13 cluster. See here(https://youtu.be/ILnuBpDCJTk). Almost everything in this video is driven of the CAN Bus. The Oil Pressure, Fuel, Voltage, PRND are driven off direct lines so to move them with CAN I had to use the "Techstream Diagnostic" messages.

 

Is it the maestro or your radio headunit? I thought most aftermarket headunits had the ability to program in custom gauges.

 

That’d be awesome if you got the chance, no need to make it a priority… and to be honest whatever you come up with probably wouldn’t work with my truck as it’s the 4.7 and not 5.7

 

Need a 4.7 to log, I wonder if tell Techstream my truck is a 4.7 would show the difference in data location..

 

I’ve got Techstream, I could log it?

 

But also the transmission is entirely different so I don’t think that would work

 

Do you guys have the equations to read tire pressures?
I think some versions of the scangauge can display it (part of xgauge?) or it can be programmed using xgauge.

 

My '94 80 series had this dead zone issue, the hack was a resistor that made it actually move.

 

Look here,3 different options for TPMS on Toyota as the programming changed through the years. https://www.scangauge.com/support/x-gauge-commands/toyota-lexus-scion/

 

I think this should work. I had to study the X Gauge format a little bit. I logged it in Techstream and ran it in my OBD Fusion App no problem. Converting to Scangague format could be the only issue. This is on my 2007 5.7 truck

Longname: Transmission Gear
SG2 TXD: 07E021DA
SG2 RXF: 046105DA0000
SG2 RXD: 2808
SG2 MTH: 000100010000
SG2 NAM: GER

 

Thank ya man! I’ll give it a test, currently my truck is torn apart for the rear diff so once I get it back together

 

All good, I am pretty sure I got the scangauge format right but would be interested to hear if it works. Will display 1 all the time until it shifts up 2-6

 

It was the coolant temp, it’s funny. I have not seen a response to the thread in a long time and one just came in.

https://forum.ih8mud.com/threads/93-97-coolant-temperature-gauge-modification.64252/

 

so bad news, doesn't work with the 4.7

 

Jeff, in your review of schematics and knowledge of truck and engine, is there an engine oil temperature thermistor anywhere?? You gave me a link to searchable schematics and I don't see it for my 2010 4.6.

Again, messing with phone app OBD Fusion and oil temperature PID and I think it seems to be close to accurate. Things that say they are calculated are just that a calculation. This doesn't say that.

I intend to do a verification using an IR gun to the pan and see how close the temps are. I'll keep you posted. Having not found it on the schematic, it must be a calculation using water and ATF temp or something?? IDk...