computer codes I do not understand

[92 sport]

I have a 92 sport with a 4.0L 5sp 2x4. The computer is giving me two codes that I do not know how to fix. The codes are 211 and 556. The code 211 kinda understand but 556 I have no clue. The description of code 556 is primary fuel pump circuit failure. What could cause this code and how can I fix it. Thanks for the help
92 sport

 

[MrShorty]

Basically two things that cause a 556: Either the fuel pump circuit is open, or the monitoring circuit (between the fuel pump circuit and the computer) is open. Get a wiring diagram and a voltmeter and see where the fault lies. Is the 556 a KOEO fault or a continuous memory fault? If a continuous memory fault, then the problem is probably intermittent, which will make it difficult to diagnose.

 

[92 sport]

I think the 556 is a CM fault. Would this be caused by a gas guage not working? The gas guage has not worked for some time and now the truck has a real bad hesitation. When I get on the gas it feels like it cant find gas. I went over the codes the computer is giving me and than I get the 556 i an stumped.

92 sport

 

[MrShorty]

I don't think the gas gauge could cause a 556. I'm pretty sure a 556 refers to a fault upstream (electrically) of the point where the computer monitors the fuel pump circuit. If it were me, the first thing I'd do with a CM code like that is to clear the CM codes (pull the jumper wire during KOEO test) and see if the code(s) come back. The 211 is also probably a CM code, so both codes will be cleared.
Do you get a pass code for the KOEO test? If so, do you get any KOER codes? If not, then you need to work on any KOEO codes first.

 

[92 sport]

well the codes went like the 111,111,1,211,556,211,556 what i was reading was the pass code twice than the other codes. twice. and what is that single 1 in there?

92 sport

 

[MrShorty]

Yes, that means it passed the KOEO test, and the codes you are listing are CM codes. The single 1 is called a "separator pulse" and is used to separate the KOEO codes from the CM codes. So, have you tried the KOER test? Best practice when diagnosing trouble codes is to resolve codes in this order: KOEO codes (you're already passing this), KOER codes, and finally deal with any CM codes. The next thing to do would be to run the KOER test. Watch the procedure and be sure to warm the engine up before doing it. It's easy to get false codes from the KOER test by a) running it cold, b) forgetting to step on the brake after engine id is output, and c) by neglecting the dynamic response (aka "gooose") test.

 

[92 sport]

ok yeah i did the koer test before i cleared the codes. it took me three tries I got the 538 or operater error three times on the fourth try i did not get any codes at all. should i try it again with the other codes clear?

92 sport

 

[MrShorty]

You didn't get any codes at all as in you got a pass code (111) or you really didn't get any output at all?
It doesn't make any difference to the KOER test whether or not there are any codes in CM. KOER codes, like KOEO codes, represent faults present at the time of the test (aka hard faults). CM codes that aren't accompanied by similar KOER codes suggest that the fault is at least somewhat intermittent.
My strategy would be to clear the CM codes, drive the truck, and see which code(s) come(s) back. If both codes come back, pick one of them (usual procedure is to pick the first one output) and resolve that code. This one could get interesting, so be prepared to exercise some patience. Also, if your local library has good manuals, pick up a copy of the circuit "pinpoint" test for each code you get.
Good luck and let us know what happens.