PO251 and Optic Sensor Troubleshooting

Customer Reports:

"Pull out onto the main road, rpms only go to 2200 and no power. Lags at 2200 for a moment finally shifts to second gear. This repeats into 3rd and 4th. At this time I see the SES light come on. I check the code with the torque app, P0251.

Truck would eventually get up to to the speed limit, 50, but took a solid mile to get there."

Quadstar Says:

This is either an optic sensor failure or fuel supply/contamination issue or wiring issue that's causing the computer to go into limp mode/backup fuel mode. That's your loss of power and drivability cause.  You can use the torque app to monitor Desired Timing, Actual Timing, and cam references missed. If you see actual timing go to 0* then you know the optic sensor signal went away. The computer can't measure actual timing without the optic sensor working and will show you when there's an issue.

How to fix this? That's hard from here. We can only give you ideas especially on a used pump.  We could assume everything on the truck is fine and tell you: ya, the pump is bad. But that might not be it. You could put a new pump in and have the same issue if the problem is in your engine wiring harness, fuel contamination/air in fuel, etc.

PO251 is specifically the camshaft position sensor (low resolution) track of the optic sensor. Proper scan tools will show cam and crank position references missed and you can disconnect one or the other and see if the engine will run in backup fuel mode. Our other articles have some more detail on that.