Can a variable be locked at hardware level ?

[Vertinhol]

I changed out of curiosity the max speed variable of my car ECU from 250Km/h to 60Km/h to see if the car reach that speed and hold there or I can go beyond and get a notification but it turns out that I cannot exceed that limit.

Now, I'm unable to get the speed to its original value nor increase it, I found out later that this particular variable can only be decreased... My local car dealer (VW) doesn't know how to fix it, so I had to rely on third party mechanics specialized in ECUs but unfortunately so far no one have figured out the solution, even after re-flashing the entire ECU.

I got the reference of my ECU chip which is UN92CB but I couldn't find any datasheet, so I was wondering if it is possible to hardware lock a variable from increasing, so I can just buy a new ECU instead of losing my time figuring out the problem.

[AScha.3]

usually not. but if special hardware is built for this - yes.

i remember these early chip-cards for public phone, they had such "variable" on the chip.

that was the stored money value and it would call all hackers, how to increase the value. 🙂

i found out, how it was done: there was a separate area on the chip, with a kind of eprom cells, all "1" when new. Using some of the money did just set some to "0" . every bit was 5 cent or so and this way they could sell cards with 10 euro on it and using could only reduce the value, never increase.

maybe you found something similar.

then last chance: set in new chip and flash.

if its the chip, seems not expensive, but there could be some "key" also, so it refuses new blank chip.

but this could only show a test. $12 test.

https://www.ebay.com/itm/5pcs-UN92CB-ATIC92C2-automotive-computer-board-vulnerable-chip-chip-36-feet-new-/123206076369

[Vertinhol]

Thank you for your answer, I really thought about an entire separate chip at first that contains this particular value and other ones with similar properties, and it could also be a region as you mentioned but I cannot be sure unless I have the datasheet which is not available.

Unfortunately like I hinted, I live in a stupid country, where even the car dealer doesn't know any fix, they refuse any problem related to the ECU, so I had to rely on third party specialists to figure out the issue, so far I found a good one that accepted the challenge and have very expensive tools, but I can see that he's struggling, he extracted the program inside the chip and sent it to pro tuners in Germany I believe or Italy to fix it and reflash it again, which what I have tried today but no luck.

I suggested to him different ideas such as:

• Decrease the speed limit to 59Km/h and re-flash again with the old extracted file that have the 60Km/h limitation to see if the value can be increased or not.
• In case of an increase we can do the same thing many times for different lower values and compare each file until we find the region responsible for this mess.

He didn't want to try my idea and I'm looking for an alternative way to know if this region is hardware locked or not so i can skip an entire chapter of seeing him trying in vain.

I don't have any problem if the speed limitation gets very low (I don't know the lowest value that can be achieved but I'm sure it's not zero, don't ask me why) because I can easily remove the speed sensor and drive as fast as the car can go :p

Of course this means that the car doesn't count anymore the kilometres I travelled (I can sell it later at a high prize, joking) but in the other hand, I don't know when I need to change oil, also the ABS and power steering will not work, and some other minor issues like engine breaking is very rough.

[AScha.3]

i would also assume, it is just a value in a separate memory area for values, that should "stay with the car", like driven km or serial no. , not a telephone-card like special chip. (this was just to your question.)

so you need someone, who knows how to chance these flash area, like the total km distance.