pcmhacking.net

Could some one please shed some light on as to how this could happen please...

So I had a 2007 toyota coaster bus in with a blocked dpf, fixed that and replaced shitty pressure sensor, had a hard code p2002 to do with dpf threshold exceeded? Or something like that anyway, after heaps of wasted hours and six different scan tools, i rang a mate at toyota who said "had that issue on a hiace, disconnect and reconnect the battery and that will solve it.." To which i called bullshit so after grumpiliy doing as suggested, volia, fixed didn't even have to try to clear codes, all done for me

WHAT THE FUCK....

How can that happen?

One word "Japanese" ! They do some weird shit lol

Sounds like a software bug. Probably does not clear the code out of ram when it should but the battery finishes the job as a work around.

because most codes are stored in the area of the computer that needs power to remember them, if you remove constant power from most computers it clears codes and a lot of learnt settings and such.

I remember working with Japanese OEM's when brand sharing, would go to them with a vehicle problem and get standard response over and over again.
No problem
No problem
No problem
Then all of a sudden get a response
Problem fixed

They would never admit there was a problem, then they would fix it but not tell you what they did.
Extremely frustrating

So the fault code is stored in the ram? So why do some modules maintain their memory no matter what the power supply does? Eg: airbag module with deployed bags, vt commodore srs faults, and every other pcm I have ever connected to, etc...

some write to ram, which looses it's contents when powered off, some write to eeprom memory which doesn't. All systems have both types, it's upto the programmer to write the code, so it's there choosing where things are stored.

For Holden PCM's fault codes are stored in ram, so it's lost when powered off, but a history code is also written to internal memory, so it is not lost when powered off.