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!