What's this code?

[leeunderwood2000]

I went to auto zone to get my code scanned due to service engine light coming on. It said PO 251 Injection Pump Metering control A. Did a search for this here and nothing. Anybody got any ideas? Thanks in advance.

Lee

[GARY PAGE]

Ask them to give you a code key which you stick up the connector and count the check engine light flashes. If you can't find the code here not valid is my guess and there something up in the scanner.

[ucdavis]

0251 is Injection Pump Cam System circuit. That is the black gizmo ("optical Sensor") on top of IP. Same as code 18 on the 94/95 rigs.
The gizmo reads a rotating disc inside the IP to tell PCM where in cam rotation the pump is. PCM matches these readings against the crankshaft position sensor readings to assure appropriate timing of engine controls.
You can get this code if you run out of fuel (get air in the IP), or run low and are "performing hard acceleration or turining maneuvers," have poor connections on IP or PCM or the wires between the two have rubbed to where you are getting leakage of signal, or have broken wire inside the insulation. PCM will have stored Freeze Frame and Failure records for a tech to read w/a Tech2 or equal scanner.
If this is intermittent, it will clear the MIL light after 3 consecutive trips w/out the fault.
First check all connections & wiring for shorts or non-contacting conditions. If everything in engine box looks OK:
Sensor has 2 wires to it if I remember; you should have 5 volts +/- 0.2, and 50mA @ the hot wire w/key on-engine off, and good ground to the other. If you have a 10 meg-ohm multimeter w/Hz scale, look for 57-63 Hz on the brown-wire-w/white-stripe @ terminal A4 @ PCM w/engine running @ 900 rpm (or you can factor the Hz down proportianately to your idle rpm (idle of 450 = 1/2 the Hz, etc.). If the voltage is high it will probably be 12.6V and you have a short to battery voltage & need to find it; if it is low, you have short to ground or open/partially open circuit & need to find the interruption.
If you find the gizmo is bad, you can replace it yourself if you pay mucho attention to cleanliness. Once you commence removal, you will be opening the IP & will contaminate it if dirt or ?? falls in. Clean off top of pump & all around the 'operating area' first (actually first find a Stanadyne dealer & get a new sensor & O-ring) then remove the torx screws, lid, circlip, slip sensor upper piece out of lid, remove big torx screw on lower sensor piece and carefully remove the loser sensor from the thin metal ring that rides in sensor's slot. Install new sensor in reverse order of the above. Activate Lift pump to purge air from IP (w/engine off) & let run for 30 minutes or so. Key off & let rest for a while, then start up.
If you do this, post your findings & success. And I almost forgot, if you have less than 120K miles, forget the whole thing & let the GM dealer handle it under the IP extended warranty which is way better than this messing around. Also, the dealer has a scanner that will do some additional tests B4 replacing anything.
And you might check your fuel filter; I have a theory that this code can come from contaminated fuel getting into the IP; the holes the sensor reads are real tiny and any blockage could cause a misread hole.
Good luck; sorry for long post.

[leeunderwood2000]

ucdavis,

Thanks for the info. Brought to dealer and he says IP. He's ordering one now and it will be in Monday. Wednesday they will install. By the way it is under warranty.

Thanks,

Lee