Mode $3F - Test Device Present, Whats it do?

[Keith@HPTuners]

Throwing this out on the bus doesn't seem to affect the activity at all.. anyone know what looks for this?

[jfunk]

Maybe, you need to start in Mode $10 and Mode $3F just keeps the modules on the network from leaving the diagnostic state. Just an idea, but the modules might not respond to Mode $3F unless their in Mode $10(Initiate Diagnostic Operation)

[ls1tools]

What jfunk said is right...

Modules are designed *not* to respond to the $3F mode.
If a response were to be sent it would be ($3F+$40) $7F: General Response - but modules, as a rule do not respond to it.

The purpose of $3F is a "keep alive" signal.
If the scan tool has requested a certain diagnostic mode then the module or modules in those modes will stay in those modes as long as they "see" this $3F message periodically.

It's a safe guard for if/when a scan tool is removed from the network without signalling to the on-board modules that it has finished. (i.e. someone just pulls the plug). Modules can safely "return to normal" and not remain in a "diagnostic" state.

Paul

[Keith@HPTuners]

Thanks for the info guys.

I have to do some more testing, perhaps this will keep the PCM unlocked during an idle process for an extended length of time.

[Keith@HPTuners]

I did my testing and am able to keep the pcm unlocked indefinately using mode 3F.

In PCM_Edit, I just setup a timer that sends it every 3 seconds in my flash read/write form (not released yet).

[jfunk]

Is three seconds the timeout period before the modules start talking in normal mode again?

[Keith@HPTuners]

I believe its about 5 seconds.