I took the War Wagon down to the Family Dollar down the road (~3 miles) and the check engine lit up. It ran as normal (indifferently), and when I started it back up the light stayed off. I checked the codes when I got home and saw:

12 (normal)

33 (A/C relay? This truck has never had A/C installed.)

37 (Trans Lock-Up Solenoid? It has no TCC)

41 (Alternator Field Control. Not sure what this one means.)

42 (Auto Shutdown. This has to do with the ASD relay, I'm guessing.)

22 (ECT Sensor. The guage seems to be working.)

11 (Pick-up signal. I replaced the pick-up coil last summer.)

If anyone knows if these codes mean different things than the list I found when applied to a '91 D250 318 with an A518 trans, I'd be thrilled to hear from you.

Thanks in advance for any help!

 

Clear the codes, drive it and re-check them. Some of them may be left overs or ghost codes.

 

X2 on that

12, 33, and 37 will never go away, they don't hurt anything, but they will always be there because the computer looks for input and doesn't find anything. 41 deals with the charging system. I just dealt with this one, my truck slowly started having erratic charging. I ended up replacing the ECM to fix the issue. But, before trying to diagnose anything, clear the codes, drive it for a bit and see what comes back.