I'm trying to get codes from my 94 B4000. The Cel on the dash is not working even after changing bulbs and checking fuses. I don't have an analog multimeter sim using a test light on the sto port of the eec connector. With the light going from sto to the positive terminal and the jumper wire going to the sig term I get a continuous light on when I koeo. No flashes and the light doesn't go off no matter how long I leave the key on. If I start the engine, the light goes off for a few seconds and comes back on. It's like the self test mode isnt working and I've tried different jumpers. The truck was submerged underwater for two days prior to me getting it so there's that too.

 

The CEL in the dash gets 12v with key on

The PCM Grounds it when it boots up using pin 17 of the PCM
This "ground wire" is also on the self test(OBD1) connector

Fuse 7 in the cab fuse box powers the CEL bulb, along with other dash lights and gauges

Have a look here: https://www.therangerstation.com/tec...ry/OBD_I.shtml

The self test OUT on the connector is the CEL bulb ground from pin 17 on PCM

Yes if you place a jumper between self test IN and Sig-Return, that should put PCM in test mode

Test light(or CEL) should come on and then go off and flash 3 digit codes

So could be PCM's pin 17 and other pins are shorted to ground full time when power is applied to PCM

4.0l wiring diagrams here:

 

Thanks Ron. Got the pcm out now. Lots of moisture between it and the connector. Took it apart and besides some rust on the mosfet? Behind the heatsinks the board looks ok visually. I'm going to dry the connector pin area up and see if anything changes. In the meantime I'll look for a pcm to replace this one.

 

I've got a crazy idea but not sure if it'd work. It depends on if the pcm remembers codes. If so I have a 94 ranger but it has the 2.3 in it. Could I hook the B4000 pcm to the ranger and check the codes stored on it that way to see if I'm getting a pcm fault code?

 

The codes may already be cleared once the battery power/the 60 pin connector, was unplugged
But you could try, but I don't think the wiring in the B4000 was the issue, water in connector was

Rinse connector out with distilled water then dry it(hair drier) or let it dry

Yes if there was water in the connector that would cause short to ground, so CEL would not flash codes

 

Ok after cleaning it a bit a bit I've got the cel on the dash illuminated. Still just stays on like the test light. Progress none the less. I'm going the clean the connector now too and see if there's any change.

 

Just found something on a mustang forum where guy had a similar problem with eeciv not dumping codes. One of the last suggestions was to ground the self test wire ,grey and white single wire, and see of that works. It worked. I've got to record all the codes and see what's what but it's now working by grounding that wire.

 

Ok here's the codes from key on engine off I get and what I think they mean:
116 ect out of range
121 tps out of range
114 out of range
327 egr low or no feedback
522 clutch in during test
341 octane jumper installed
543 fuel pump monitor shows no power

Will try key on engine running diagnostic after clearing codes next

 

Couldn't get key on engine running test to run, cleared codes and ran engine to operating temp and ran koeo again and came up with following codes:
118: Ect is/was high or open
123: Tps is/was short to power
113: Iat is was high or open
327: egr feedback is was low
522: clutch in during test
539: system shows voltage at pin 10 a/c on?
341: octane jumper installed
542: fuel pump open bad ground or always on
Spent 20 minutes trying to get truck restarted after warning up to test koer, finally started not sure cause of no start.

 

Does #542 point to a bad or badly connected fuel pump? This goes to your hard starting.
Does #123 point to a bad throttle positioning sensor?
Does #113 point to a bad Incoming Air Temperature Sensor? The car thinks it's warmed up and doesn't choke(?) In '94 is the MAF and IAT a combined part?

 

I googled the codes to get the info I posted. No the Maf and Iat are separate. I think I may have ran it out of gas as the hand on the fuel gauge always reads over full so I cant tell if its empty. It quit again after it restarted and only restarted after I put a gallon of fuel in the tank. Will look at pulling the pump and investigating the breather hoses on the tank anyway due to the hand not working and the filler neck takes gas very slowly.