3 ms·

I think that was "versus replacing a chip." The ECU has fairly standardized interfaces, mostly CAN or just simple switching circuits on or off. You can just ge

by lambda 2y ago

I think that was "versus replacing a chip." The ECU has fairly standardized interfaces, mostly CAN or just simple switching circuits on or off. You can just get a replacement ECU. These replacement ECUs generally don't do things like using the O2 sensor to adjust the fueling, so they can burn dirtier than the original ECU.

noprocrasted 2y ago
> mostly CAN CAN is just the physical and framing layer. The data that goes over it is a whole different matter, and it's proprietary to every vendor, incompatible and generally undocumented. For a lot of cars you can't even swap the exact same ECU between vehicles (due to bullshit like the VIN being written into it for no reason, and often no official way to change that other than "buy a new module" - so you have to hack around with reverse engineering & EEPROM programmers), let alone mix and match completely different parts.
- bluGill 2y ago
  > the VIN being written into it for no reason There is good reason for this: theft protection. A long known crime model is the "chop shop" where they tow away a car, then cut it up for parts. Because the VIN is in the ECU a chop shop has less incentive to exist since there is less money in it. It does of course make legitimate repairs harder, and probably there should be a process to write a new VIN in - but it should only be available to someone who can verify the ECU wasn't stolen (which isn't free).
  - noprocrasted 2y ago
    EEPROM programmers and various other ways of rewriting this VIN (turnkey tools using undocumented diagnostic commands giving you unauthenticated read/write access to memory) means it's just one insignificant expense for the chop shop (as it's amortized over all their cars) vs a multi-thousand-dollar investment in money for a legitimate vehicle owner or part-time mechanic.
    - bluGill 2y ago
      Only if it is done via EEPROM and not via something more complex. Though your point stands.
- lambda 2y ago
  That's true, but it's usually pretty simple to reverse engineer, and that's been done for a lot of cars. CAN message are generally sent out at fixed time intervals, and correspond to some physical or control value, with a simple linear mapping between some physical unit and the value in the message. You collect some CAN data, change something like pressing the accelerator, see what changes, record results. Just search for "aftermarket ECU", you'll find lots of them; generally for high-performance cars that gearheads want to soup up further, but the same basic principle applies to most ECUs.

by lambda 2y ago

noprocrasted 2y ago

> mostly CAN CAN is just the physical and framing layer. The data that goes over it is a whole different matter, and it's proprietary to every vendor, incompatible and generally undocumented. For a lot of cars you can't even swap the exact same ECU between vehicles (due to bullshit like the VIN being written into it for no reason, and often no official way to change that other than "buy a new module" - so you have to hack around with reverse engineering & EEPROM programmers), let alone mix and match completely different parts.

bluGill 2y ago
> the VIN being written into it for no reason There is good reason for this: theft protection. A long known crime model is the "chop shop" where they tow away a car, then cut it up for parts. Because the VIN is in the ECU a chop shop has less incentive to exist since there is less money in it. It does of course make legitimate repairs harder, and probably there should be a process to write a new VIN in - but it should only be available to someone who can verify the ECU wasn't stolen (which isn't free).
- noprocrasted 2y ago
  EEPROM programmers and various other ways of rewriting this VIN (turnkey tools using undocumented diagnostic commands giving you unauthenticated read/write access to memory) means it's just one insignificant expense for the chop shop (as it's amortized over all their cars) vs a multi-thousand-dollar investment in money for a legitimate vehicle owner or part-time mechanic.
  - bluGill 2y ago
    Only if it is done via EEPROM and not via something more complex. Though your point stands.
lambda 2y ago
That's true, but it's usually pretty simple to reverse engineer, and that's been done for a lot of cars. CAN message are generally sent out at fixed time intervals, and correspond to some physical or control value, with a simple linear mapping between some physical unit and the value in the message. You collect some CAN data, change something like pressing the accelerator, see what changes, record results. Just search for "aftermarket ECU", you'll find lots of them; generally for high-performance cars that gearheads want to soup up further, but the same basic principle applies to most ECUs.