Auto transmission vs. manual transmission ECUs?

[Kha0S]

My factory ECU is an AF411 (auto transmission) 02 WRX unit with an A4SG900C CalID. Now, as far as I know, any of the AF41x ECUs (AF411, AF412, AF413) should be reflashable with the A4SG900C ROM and run just fine.

My question is, is it possible to take an AF42x (ie, AF423) manual ECU and flash it with the other ROM and have it run appropriately? That is, is the logic for AT vs. MT embedded in hardware, or is it simply a flash issue?

To complicate things, I've done an MT conversion on my AT car, so I've actually done some harness modifications to "convince" the ECU that it's in an MT vehicle.

I'm going to do some more IDA disassembly today and see if I can figure out where the ECU determines which vehicle it's in.

[Kha0S]

Okay, so far, I've found both an AF411/A4SG900C ECU ROM (02 WRX auto) and an AF421/AfSG900C ROM (02 WRX manual). Both the CPU and TPU codes are identical.

I'm looking through disassembly right now... it looks like there's a variable at 0x2195B that is used as a "flag" byte, part of which (the 0x08 bit) is used to select automatic vs. manual boost maps.

Question is, if the CPU and TPU code is the same, there must be a physical response somewhere setting that bit.

/Andrew

[qoncept]

I was just going to tell you someone was using an AT rom in an MT and grounding a pin on the ECU to make it work.. but I think that was you..?

[Kha0S]

I was just going to tell you someone was using an AT rom in an MT and grounding a pin on the ECU to make it work.. but I think that was you..?

Yup.

Problem is, the car still uses the AT boost tables, and not the MT tables, which means that somewhere in there, it's still figuring out that it's in an AT vehicle.

Question is, is there any physical difference between an AF41x and AF42x ECU? They're different part numbers, presumably, for a reason...

[diablerouge]

not sure if anyone has thought of this or not, but if we can figure out how the ecu decides which map to use, we could easily switch between two different sets of boost/ignition/fuel/wastegate maps. if the input is a grounded wire, even easier. this would allow a high/low boost or economy, or whatever you wanted to switch between. now i just wonder if there are any differences in code between the auto and manual transmission ecu's? anyone know?

[Kha0S]

not sure if anyone has thought of this or not, but if we can figure out how the ecu decides which map to use, we could easily switch between two different sets of boost/ignition/fuel/wastegate maps. if the input is a grounded wire, even easier. this would allow a high/low boost or economy, or whatever you wanted to switch between. now i just wonder if there are any differences in code between the auto and manual transmission ecu's? anyone know?

The code is identical, and the hardware appears to be identical.

I'd watch out on grounding/ungrounding the pin, though, as that tends to make the ECU throw some other codes (ie, AT diagnosis signal errors).

/Andrew

[Jon [in CT]]

I'd watch out on grounding/ungrounding the pin, though, as that tends to make the ECU throw some other codes (ie, AT diagnosis signal errors).

/Andrew

Those codes, of course, could be cancelled.

[Kha0S]

I'd watch out on grounding/ungrounding the pin, though, as that tends to make the ECU throw some other codes (ie, AT diagnosis signal errors).

Those codes, of course, could be cancelled.

Indeed, but I actually think that that MT/AT identifier pin is barking up the wrong tree. I grounded mine when I converted my car from AT to MT, and the car stopped throwing the AT codes... but still uses the AT boost maps out of the ROM.

I compared the A4SG900C images from an AF411 (AT) ECU and an AF421 (MT) ECU, both CPU and TPU areas, and they're identical. Colby confirmed that the board inside the AF411 (and, by extension, all 02/03 AT AF41x ECUs) is identical to the AF423 (and, therefore, all 02/03 MT AF42x ECUs). So, the hardware is the same, the software is the same...

But somehow, my ECU still "knows" that it came from an AT. I've attempted to disassemble and figure out the code that sets the identifier flag in RAM to pick AT vs. MT boost maps, but it's embedded into a sort of initialization routine that does an awful lot of flag setting and switching, and I ran out of brainpower before figuring it all out.

/Andrew

[RallyImprezive]

Nice research man. Good content!

[west_minist]

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