MSefi.com read only forum (Jan.15,2018)

Has anyone tried to emmulate the ALDL and Service Engine Soon light on a late 80's GM car? I would at least like to have something that turns on the SES at key on with engine dead and flash a code 12 when the ALDL signals are shorted.

Thats got to be easy if you wanted to make a seperate module.
You just need to program a pic or the like to do this.
1. Upon power on,turn cel on then off.Then time while monitering rpm in and if there is none in the given time, then turn on the CEL.
2. If the rpm stops and power still on then turn on CEL
3.Moniter the the ALDL wires and if they are shorted Flash the CEL 12 times then wait and repeat till wires not shorted.
This has to be to in order to get around some sort of Gvt mandated testing?
Or maybe just for fun?

slow_hemi6 wrote:Thats got to be easy if you wanted to make a seperate module.

This has to be to in order to get around some sort of Gvt mandated testing?
Or maybe just for fun?

This is purely for fun, of course!

The Service Engine light is more for a reminder that says ' hey, the key is on but the engine isn't running.' I'm thinking maybe a 555 timer and a latch would do what I want.

As for the code ... my thought was to just program a serial EEPROM with the appropriate bit pattern and then use a free running counter to generate the address lines.

Thats where the microcontroller is a thing of beauty.You could do something through hardware, but 1 pic the size of your 555 could be 70 to 80% of the parts needed.