Possible causes

– New PCM-Needs programming
– Incorrect VID configuration

Tech notes

After a new PCM has been installed, the Vehicle Identification (VID) block has to be program to the PCM.

There is a service bulletin for the P1639 code for the following models:
1999-2002 Ford Mustang
2000-2002 Ford Focus
1999-2002 Ford Expedition
1999-2002 Ford F-150
2000-2002 Ford E Series
2001-2002 Ford Explorer
2001-2002 Ford Ranger
Ford Factory Service Bulletin OBDII Code P1639

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1639 FORD Description

Vehicle ID block is not programed or is corrupt

FORD Technical Service Bulletins for P1639 code