replacing ecm?
 

finally got a spare used ecm for my lbz (my stock ecm was in a wreck and has a gap in the housing but still works!so i want to change it before water gets in)but when i swap them the truck wont start? the security light on the dash stays on instead of going out after 5 seconds or so like normal...how can i get the other ecm to work ???was told i dont need to flash it to my vin #, i'm installing an alarm soon which means disableing the factory security system.will this make it work or is my problem from deeper inside the engine security system???is it just my ignition key because it doesnt match this other ecm's original key values??

ECM needs to be programed to the same options to the one that came off the truck

you can try the relearn procedure

bump over the engine with the key (dont turn it on) and then leave the key in ON for 10 minutes until the security light goes off. then turn OFF the truck for 5 seconds and repeat two more times.

You must turn off the truck before attempting to start it again every time

i'll try that relearn procedure.but if that doesnt work can it be done with efi live?

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thanks phil the key on for 10 min.x3 worked great security light goes off and truck starts now!but now its throwing three codes,u0100 "see shop manuel",p0182"eng. fuel temp sensor circuit low input",and p0700"tcm requested mil illumination".so are these old codes from the truck i got the used ecm out of?i cleared them three times and they keep coming back? i had no codes at all with my original ecm?keep in mind i just put in a new N.A.D.P stage 5 tranny.300k on it so far.thanks guys for the help

hmm dont know what would cause the codes to happen unless theres something wrong with the fuel temp sensor, you can try and follow he wires from the fuel temp sonsor and make sure theyre not loose or messed up at the ecm wire harness.

btw names danny, phil in my avatar is 2001shortbedcummins