Update to adding trans temp gauge...

[DougAMiller]

Well, it has been a long, long time figuring this out, but I believe I have got it. I'm referring to a thread I started last year about configuring the instrument cluster for adding the trans temp gauge.

https://www.tahoeyukonforum.com/threads/reconfiguring-instrument-cluster-with-tech2-and-tis.99740/

Turns out, the Tech2 isn't needed, but an eeprom programmer is. Good news is, they're a lot cheaper than the Tech2. You can pick up a cheap one for $30.

Anyway, after a lot on research, it became clear that there are a number of parameters that are stored in an eeprom (U15) in the cluster. Odometer, engine hours, VIN trip meters, some other identifying information, some vehicle settings, and still quite a bit more that I haven't figured out yet. There are 256 bytes on this eeprom, and I've deciphered about half of it. I originally theorized that the cluster model (there are a lot of cluster models for the GMT800) information stored there was what was used to determine if a trans temp gauge was present, but as it turns out, it is just a byte in the vehicle settings block that is set to 0x01 for no gauge and 0x00 if the gauge is there. I have managed to find a handfull of memory dumps from different clusters, and bought a Denali cluster off ebay to play with. And from these I have wasted many hours, well at least my wife thinks they're wasted, figuring out what and how these parameters are stored. I still need to pull the cluster from my Tahoe and reprogram it, but I have successfully turned the trans temp gauge on and off on the Denali cluster (I used my Tech2 to sweep the gauges to see that the gauge operated or not).

So, HOORAY and success!

 

[DougAMiller]

Here is a bit of what I have figured out.

The odometer value is repeated three times for data integrity. First two bytes are the most significant and the least significant byte is roved over the next 10 bytes since this is written every 1/10 of a mile and the EEPROM is spec'ed for 1 million write cycles. This would stay within spec for 1 million miles.

Engine hours is stored once as four bytes, although I can't imagine needing the fourth byte, divide by 10 since it is recorded to 1/10 of an hour, and it is stored LSB→MSB.

TransTemp 0x000059 0 - Yes 1 - No

Vehicle Settings
0x00005A 0 - English 1 - French 2 - Spanish
0x00005B 0 - Imperial 1 - Metric

The VIN is stored as plain text, that is, the characters are encoded in ASCII and written as hex.
Last 4 characters from label bar code stored as plain text, serial number maybe?
GM 8 digit Part Number for cluster is stored in hex format MSB→LSB
Cluster model ID is 4 large characters from the label. Also stored as ASCII plain text.
Trip meter value is in speedometer pulses, e.g. miles = value/4000, it is stored LSB→MSB. Took me a while to figure out how they were encoding this, but it means that your trip meter is accurate to about 15 inches!. It's probably only updated in volatile memory and stored periodically or at shutdown, otherwise it would wear out the memory location pretty quickly.

Not stored in cluster:
Vehicle settings menu, except language (1) and units (2)
Timer
Fuel used

Gray blocks are the same in every memory dump I have looked at, and are mostly zero and probably unused. Still trying to figure out the gauge calibrations, which I think are stored somewhere in the white blocks.

 

[HiHoeSilver]

Omg you're a genius! Waiting for link to programmer and detailed how to. Will send your wife a pair of shoes if need be.

 

[DougAMiller]

This is the eeprom programmer that I have

https://www.amazon.com/gp/product/B07CDD9PGT/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

but there are quite a few that are much cheaper and should work on this chip. Mine is able to handle a lot of different eeprom's which is why it costs more. It just needs to handle 25020 eeproms. Here is one that should work as well

https://www.amazon.com/Zoomarlous-E...m+programmer&qid=1552446634&s=gateway&sr=8-34

it also comes with the in-circuit programming clip which makes it much easier to do. Otherwise you would have to unsolder the chip to put it in the programmer socket. I've done all of the reads and programming in-circuit, it's a piece of cake.

 

[DougAMiller]

Oh, also in another post, I was assuming that some kind of checksum would be calculated when writing data to the eeprom, but at least for the parameters that I have figured out, that doesn't seem to be the case. So changing odometer and hours on a used cluster to match the vehicle it is going into should be pretty straight forward.

 

[drakon543]

wow so technically it would actually be really easy to pull the gauge cluster and roll the odometer back. well easy for someone who has a programmer and figured this out already. if you figure that part out i hope you dont post it.

 

[08HoeCD]

Thank goodness there are smart, patient people like the OP in this world.
I'd never be able to figure this stuff out. lol

 

[Rocket Man]

Good info. Following.

 

[DougAMiller]

wow so technically it would actually be really easy to pull the gauge cluster and roll the odometer back. well easy for someone who has a programmer and figured this out already. if you figure that part out i hope you dont post it.

The fact that something can be used for a bad purpose shouldn't negate it's use at all. If someone wants to do this, they will find a way. The simplest way would be to just buy a lower mileage cluster and install it without putting the correct mileage on it. I refuse to subscribe to the philosophy that if someone could find a bad way of using something, that it should be made inaccessible to everyone. Besides, it's not illegal to change an odometer reading, it is illegal to attempt to commit fraud by misrepresenting the actual mileage of a vehicle.

Some of us just want to be able to do these things ourselves.

 

[drakon543]

The fact that something can be used for a bad purpose shouldn't negate it's use at all. If someone wants to do this, they will find a way. The simplest way would be to just buy a lower mileage cluster and install it without putting the correct mileage on it. I refuse to subscribe to the philosophy that if someone could find a bad way of using something, that it should be made inaccessible to everyone. Besides, it's not illegal to change an odometer reading, it is illegal to attempt to commit fraud by misrepresenting the actual mileage of a vehicle.

Some of us just want to be able to do these things ourselves.

way to throw a grenade at a pidgeon sir. if it gets posted then its also easily googled. if someone here wants the information im sure op will gladly give it up. i just asked that didnt get posted publicly so lazy aholes would atleast have to make the effort for themselves. i didnt request that op keeps the information to themself.

 

[Rocket Man]

All anyone has to do to roll back mileage is sign a piece of paper and send a cluster in to a programmer. If people want to be dishonest they will find a way.

 

[HiHoeSilver]

way to throw a grenade at a pidgeon sir. if it gets posted then its also easily googled. if someone here wants the information im sure op will gladly give it up. i just asked that didnt get posted publicly so lazy aholes would atleast have to make the effort for themselves. i didnt request that op keeps the information to themself.

He is the OP.

 

[DougAMiller]

OK, pulled the cluster out of my Tahoe this morning and programmed memory address 0x000059 with 0x00, it was originally 0x01. It was literally just flipping one bit. Drove it around enough to confirm that the gauge is now working. Interesting that the memory dumps from 2003 trucks that I looked at all were set to 0x00, which is why you can just put the stepper motor in and it works. Apparently, sometime in 2004 GM just decided to set the option to 0x01 if the cluster wasn't equipped with the trans temp gauge.

So, if you have the cluster apart to put in the stepper motor, making the change in programming only takes about a minute (you just need a programmer like one of the ones I linked to).

 

[HiHoeSilver]

OK, pulled the cluster out of my Tahoe this morning and programmed memory address 0x000059 with 0x00, it was originally 0x01. It was literally just flipping one bit. Drove it around enough to confirm that the gauge is now working. Interesting that the memory dumps from 2003 trucks that I looked at all were set to 0x00, which is why you can just put the stepper motor in and it works. Apparently, sometime in 2004 GM just decided to set the option to 0x01 if the cluster wasn't equipped with the trans temp gauge.

So, if you have the cluster apart to put in the stepper motor, making the change in programming only takes about a minute (you just need a programmer like one of the ones I linked to).

That confirms my earlier research that 2004 was the year it began to be hit or miss. 2005+ are all no go.

This is awesome. Will now be ordering my gauge face, needles, and steppers.

 

[drakon543]

He is the OP.

my apologies to doug
ill step out there hoping atleast my point was made and so i dont make a further fool of myself. plus anymore would be just be ruining a good thread.

 

[DougAMiller]

my apologies to doug
ill step out there hoping atleast my point was made and so i dont make a further fool of myself. plus anymore would be just be ruining a good thread.

No problem, and no hard feelings. Understand that my little rant is the result of months of research where I sorted through a lot of conversations in which someone would erroneously declare that messing with odometers is illegal. Simply changing an odometer is not, odometer fraud is, there is a difference.

 

[Rocket Man]

No problem, and no hard feelings. Understand that my little rant is the result of months of research where I sorted through a lot of conversations in which someone would erroneously declare that messing with odometers is illegal. Simply changing an odometer is not, odometer fraud is, there is a difference.

Exactly. I used to be an electronic technician and worked for a company that did warranty repair work for Chrysler Electronics, which was a subsidiary of Chrysler Motors, before Damier bought the company. In the 90’s they used a lot of full digital instrument clusters and they had a lot of problems with them. We programmed mileage into at least a dozen instrument clusters a day and shipped them out. Same thing was used, an eprom programmer that clipped onto the eprom chip through the back of the cluster. Didn’t even need to remove the cluster from the housing. Dealerships would send us a request for a model and mileage. I assume they would have a record of the ones under warranty but we did non warranty ones as well, so I believe they would have the customer sign an odometer disclosure form since many of the clusters we repaired would have unreadable mileage when we received them, just dashes instead of numbers. Anyway, we programmed the mileage that the dealer requested.

 

[HiHoeSilver]

my apologies to doug
ill step out there hoping atleast my point was made and so i dont make a further fool of myself. plus anymore would be just be ruining a good thread.

We know you're no fool. Don't want to screw the thread up either, but wanted to be sure you knew what I thought and I didn't come across wrong.

That said, AWESOME info, Doug. Thanks for all your work. People will do what they please with certain info, and there's nothing anybody can do to stop them. Stupid is as stupid does.

 

[DougAMiller]

Nate, or anyone else that's interested in doing this. I think once you have the programmer and the software that goes with it, it will be pretty self-explanatory how to change the eeprom. Just need to read the eeprom and change the one location as I've described, then write the data back to the chip, but I'm happy to answer any questions when you get into it.

BTW, an interesting aside, one of the things that I've seen stated many times when putting a different cluster into the truck is that the VIN of your vehicle needs to be programmed into the replacement cluster. However, I found that when I tried the Denali cluster in my Tahoe and afterward read the eeprom, the Tahoe had changed the VIN itself.

 

[mattt]

OK, pulled the cluster out of my Tahoe this morning and programmed memory address 0x000059 with 0x00, it was originally 0x01. It was literally just flipping one bit. Drove it around enough to confirm that the gauge is now working. Interesting that the memory dumps from 2003 trucks that I looked at all were set to 0x00, which is why you can just put the stepper motor in and it works. Apparently, sometime in 2004 GM just decided to set the option to 0x01 if the cluster wasn't equipped with the trans temp gauge.

So, if you have the cluster apart to put in the stepper motor, making the change in programming only takes about a minute (you just need a programmer like one of the ones I linked to).

Thanks for the great info in this thread. There is some disparity in what model year cluster can just add the stepper motor. The reason I say this is my 2004 Tahoe has a build date of 06/03 which made me think mine would be just a stepper motor add-on. With 03 being an easy add, I made the leap of faith that an 06/03 build date would have it be able to display trans temp.

However, I have read somewhere that the tell tale sign of whether your cluster will work right out of the gate with the addition of a stepper motor is that the cluster will have the light bulb for trans temp gauge pre-installed on the board above where the trans temp gauge is. My board does not have the light installed there. I have the overlay and needle but never bothered installing them because it probably wouldn't work.

Anyone else heard that one about the light being in place on the board is the sign of whether it is ready to display trans temp?

Would the OP be interested in turning on the function for other's clusters? I don't know that I want to bother with the eprom reader if it will only be used one time? What other use could it be put to? Thanks in advance.