Code 556 ... anyone?

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Jul 15, 2002 | 09:32 PM

joelb

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Code 556 ... anyone?

My 1994 Explorer Sport has a case of the go-slows. It's been pretty doggy for a while and I have the good old intermittent check engine light. The gas mileage is pretty bad, so it seems to be running pretty rich.

I get diagnostic codes 332, 335, and 556. I'm guessing that the 332 and 335 codes are DPFE related or something like that. No big deal there, but I'm wondering about the code 556 (primary fuel pump circuit fault). That's a pretty vauge description. Does anyone have any experience with this one? I don't know what condition in the engine causes this code to come up. Could it be a secondary fault related to the EGR issues, or is it a defined problem with the fuel pump?

Thanks

Jul 16, 2002 | 07:03 PM

Dialtone

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From: South Texas

Code 556 ... anyone?

[updated:LAST EDITED ON 16-Jul-02 AT 08:11 PM (EST)]I looked at the wiring diagram for 92 model and see where power from fuel pump relay to fuel pump looks like it could be monitored by PCM. Was the 556 code output as part of the Key on engine off test or during the dump of continuous monitored codes? My bet is it is an old stored code, intermittent or such. If you want to chase the wiring, 92 diagram shows a DarkGreen/Yellow wire leaving the fuel pump relay and going to both PCM connector pin 8 and Inertia cutoff switch. Your lead color could vary somewhat.
I suggest you work on the other codes first. 335 is EGR sensor out of range signal (Key on engine off self test) code 332 is EGR valve opening not detected (Continuous or engine running test). Looks like either the connector to sensor is off (open/broken leads) or sensor is bad.
I recommend fix EGR sensor problem, clear PCM memory then see if 556 code returns. That much alone should clear up majority of the doggedness problems with driveability.
Dialtone

Jul 16, 2002 | 11:19 PM

joelb

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Code 556 ... anyone?

Thanks for the reply. Here's the scoop on which code appears when:

KOEO - 335 (EGR sensor voltage out-of-range)
- 556 (primary fuel pump circuit failure)
Continuous memory - 332 (EGR valve opening not detected)
Engine running - 326 (my manual doesn't list this one, but from another post I read, it sounds like this is EGR sensor related)

I'm guessing that the 3xx codes listed are all DPFE related.

I'm in the process of tracking down any wiring fault that might cause the code 556. Since I haven't found much info in previous posts on this topic, I'll post info if anything definitive turns up.

Jul 17, 2002 | 12:20 PM

Dialtone

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From: South Texas

Code 556 ... anyone?

336 code is output as part of engine running test and is described as "EGR circuit higher than expected" I think you are back to the sensor on that one also.
556 code may indicate high resistance on the Fuel pump relay contacts leading to less than full voltage getting to fuel pump. I would stick a straight pin thru the insulation of the wire at the pcm and check with voltmeter. With the key on, you should have full battery reading from main fuse, thru the relay contacts, going to the inertia switch and then on to the fuel pump motor. Anything less would indicate some sort of problem.
Dialtone