94 ATX Code 556 & 551

[Adharan]

I’ve been having some trouble lately with the rpms surging/engine bucking at idle. It’s very sporadic and seems like it goes away once I give the car some gas - but it doesn’t happen every time I start the car either. I pulled the codes (with the paper clip method) and got 556, 556, and 551 (in that order). As far as I can tell, 556 is fuel pump relay and 551 is IAC failure. My next step is to order a new IAC and fuel pump relay (or get one from a junkyard). I’ll freely admit I’m a beginner mechanic, so if you have experience please check my work before I start replacing parts.

- is there a significance to getting the 556 code twice in a row?

- is there a common symptom that would cause both issues that I’m not seeing?

-is there a possibility the fuel pump itself needs replaced?

-is there anything I should try before I dive right in to replacing those parts?

Any help is appreciated, and feel free to correct me if I’ve gotten any of this wrong. Thanks SHO community for your time!

 

[zoomlater]

if you do a search by typing in "code 551", then another search "code 565", you can see what others have done or the symptoms when you get a code like that. Usually the codes repeat after with a break in the middle. Its possible those are old codes unless you cleared them recently. Maybe you can clear the codes first and then wait until it happens again, and confirm those are current codes.

 

[rubydist]

When you pull the codes, it will repeat them so you should see them each twice.

551 is intake runner control failure, that has to do with whether the secondaries open like they should or not
556 gets set any time the engine stalls, so can almost always be ignored.

 

[luigisho]

IAC has been a common failure part. That's not a diagnostic just some info for the mix

 

[rubydist]

So as not to confuse future readers, IAC issues are reported with codes 411 or 412. Those are not the codes reported in this thread.

 

[Adharan]

Ah thanks everyone for the clarification! Idk how I got those confused.

 

[BaySHO Performance]

When you pull the codes, it will repeat them so you should see them each twice.

551 is intake runner control failure, that has to do with whether the secondaries open like they should or not
556 gets set any time the engine stalls, so can almost always be ignored.

Correct on the 551. Take a look at the secondary butterflies and note that there's a tab on each one that can be lifted by hand. The secondaries are open engine off. When the engine is started, you should see those tabs lift up, closing the secondaries. Now rev to over 4,000 RPM and they should go down again, opening the secondaries. If they don't, it could be the Intake Manual Relay Control (IMRC) bolted to the back of the intake, the vacuum canister just to the left of it, or a vacuum leak.

556 is fuel pump relay primary circuit failure. That usually means a bad CCRM. It's usually 542: fuel pump secondary circuit failure that gets triggered if the engine stalls. Look for the large letter on it. You may be able to get one from

89-95 Electronics

shosource.com

 

[Adharan]

Thanks so much! Especially for the link. I was at the junkyard this weekend pulling a clock spring from a regular taurus. The CCRM was a match for mine so I pulled it just in case — but the guy at the counter was trying convince me it was the cars “computer” and wanted $400 for it, which I wasn’t going to do. Good to know there’s another option!

 

[Adharan]

Update: huge thanks to everyone for all the advice! I checked the butterflies and sure enough - no movement whatsoever. Pulled the IMRC solenoid and replaced it with one from O’Reillys Auto (I’ll put the part # below for anyone else who needs it) and everything is running again. Car seems to work fine, with none of the stumbling/surging issues. It cleared up the 551 code as well — I still have the 556 but I’m hoping that swapping in a new CCRM will fix that as well. Will update when I get that switched over. Thanks again for all your help!

O’Reilly’s Part # for solenoid: TCA91

OE reference #: 7L1Z9H465B

 

[BaySHO Performance]

How on EARTH did you find that was actually going to work???
Per O'Reilly it's called a Standard Ignition 2 Terminal 4 Wheel Drive Actuator - TCA91

 

[Adharan]

Truthfully, a lot of research and a little bit of shooting in the dark lol.

I found this old thread
where there’s a mention of the Expedition 4wd actuator as a drop-in replacement. I did some googling of some part numbers and found TCA91 as a replacement for the aforementioned 4wd actuator and took a shot. It’s physically pretty much a 1:1 identical copy of the OE solenoid so I figured it’d work. It’s been working fine on my test drives - I will update tomorrow if there’s any issues after I take it out on a longer trip.

 

[BaySHO Performance]

Shared this info on the Gen 1 & 2 Taurus SHO Facebook page. Other ones that came up:
With mods: Autozone Dorman 600-400, and:

https://www.oreillyauto.com/detail/c/standard-ignition/standard-ignition-2-terminal-4-wheel-drive-actuator/std0/tca91/v/a/5544/automotive-car-1991-ford-taurus?q=TCA91&pos=0&fbclid=IwY2xjawGN7npleHRuA2FlbQIxMAABHVyjSRM5EBsZQlfinBP9Dq7_ZZtx2THz0W-CqGSFCuM9bs3PEJW3TjqXmA_aem_sE_u0iatN3I7TUmZSlCdYQ

Dorman 4WD Hub Locking Solenoid 600-401

Shop for Dorman 4WD Hub Locking Solenoid 600-401 with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

This might even work:

Duralast Four Wheel Drive Actuators SW9319

Shop for Duralast Four Wheel Drive Actuators SW9319 with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com