limp 7730

[Ludis Langens]

Fisystems at aol.com wrote:
> 
> The
> problem is the thing will go into limp mode every time I shut it off and try
> to restart it. When it restarts it's in the limp mode. [...] I moved the
> battery power to switched power so that I can shut it off and than restart it
> without having to disconnect and reconnect it. With it wired that way if the
> engine stalls and the power switch is still on, I can watch the scanner lose
> communication after about three seconds. If I just hit the start button
> without turning the power off and back on it's in the limp mode. Any ideas?

The '730 has two power input circuits.  It draws most of it's power from
the (normally unswitched) "memory" power input.  The "ignition"
(ignition switched) power input mostly tells the ECM to wake up or go to
sleep.  (A few outputs are powered by the ignition supply.)

I don't know what happens when you switch the wrong power input.  It
might be that the power supply chip gets confused.


GM's software (at least of the generation that would be used in a '730)
can only handle one engine run per boot.  When the engine stalls, the
ECM resets itself.  That means it'll reboot for the next engine run. 
This also means that a scan tool will lose the connection.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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