Join Date: Jan 2009
Thanked 64 Times in 60 Posts
That PO121 code is usually a good indicator that it is the APPS(Accelerator Pedal Position Sensor). When the electronics on the VP burn out it acts the same way, but doesn't throw that code and usually doesn't throw any code. The APPS will always throw a code.
As for the alternator comment, that could be because the alternator was running too low and everything else was draining the system and nothing was seeing proper voltage.
2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.
TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)