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.