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Ford Truck PATS code B1681, or not able to Reprogram PCM
Posted to Technical Tips Forum on 5/6/2015 3 Replies

I recently have one customer that bring me his VW for AC work, but when He was ready to leave on his 2005 F150, with a V8 engine, I heard the truck was cranking and not starting, after awhile He did ask me to check his truck too, and by that time that truck it was not cranking anymore, customer stated that never happen before.

After checking for codes I found code B1681 and if I remember alright also P1601, I did check power and grounds to PATS module just to find everything OK, also security light was not blinking, however after I disconnect battery and touch cables together security light start blinking again, replacing PATS module did not change anything, and attempt to Re-program or replace PCM end up on Programming error.

One thing that I noticed when programming was failing is that on the Ignition On and OFF cycling, always fail after asking me twice to turn off switch, Problem was that ECM was never going sleep, and was staying alive even with Ignition on, After checking fuse 34 on fuse box I notice that was not loosing voltage with Key Off.

Then I remove PCM power relay and fuse 34 was feedback by fuse 32 from a bad AC relay, I found some on this information on other information sources, after a new AC relay I was able to Reprogram ECM and no more problems with PATS.

Cesar from Texas

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