trouble codes 172-176-181-185-186-332 and 556 | Ford Explorer - Ford Ranger Forums - Serious Explorations

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trouble codes 172-176-181-185-186-332 and 556

pdiddy

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December 31, 2012
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Year, Model & Trim Level
1991 ford explorer
these are the codes when engine not running. 172 and 176 refer to the o2 sensor. i havn't replaced it and have around 200,000 miles on the 1991 ford explorer. i read that it should be changed @60,000. my question is does it sound like the o2 sensor could be the source of the problem or is there more to it than just that.
 




MrShorty

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Spanish Fork, UT
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92 XLT and '87 Bronco II
With a "laundry list" of codes, the best place to start is to distinguish between KOEO and CM codes (both types of codes are output during the KOEO test). Diagnose and resolve the KOEO codes first. Of the codes listed, all must be CM (or KOER but you indicate that you haven't run the KOER test) except for the 556 code, which can be either KOEO, CM, or both. You might review my "notes on pulling EEC-IV codes" thread in the EEC-IV forum. In short, the KOEO codes come out first, followed by a separator pulse, followed by the CM codes.

556 refers to a fault in the fuel pump circuit. If it is a KOEO code and the engine won't start, you should check the fuel pump circuit to see where the break in the circuit is. If this is a CM code (pass 111 from KOEO), that suggests an intermittent fault in the fuel pump circuit. If the engine runs fine, then the fault may not be traceable. I used to get one of these off and on for a long time, and couldn't resolve it until one morning when it wouldn't start and I could finally locate the break in the fuel pump circuit.

172, 176, 181, 185 and 186 are all O2 sensor codes. It's kind of a "guess and check" approach, but at 200,000 miles, I'd probably replace both O2 sensors and see if that cleared those codes. An intermittent fault in the fuel pump circuit (possibly indicated by the 556) could also cause these codes if the break is "consistent" enough to have the pump running in spurts. The fuel pump may run enough to keep the pressure up enough to run, but the pressure may be low enough to create the lean condition indicated by the O2 sensor codes. A quick fuel pressure check should be able to identify this situation.

332 is an EGR code. Not sure that I would expect a faulty O2 sensor or fuel system problem to trigger this one. I might look more at this one after resolving the fuel system/O2 sensor codes.

Another thing I might do with a long list of codes like this is clear CM, test drive, and see which codes come back immediately, and which ones don't.
 




92exp4x4

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92 XL 2-door and others
Very strange that a '91 would have an EGR code. I didn't think any 91s had EGR. I guess anything is possible.
 




MrShorty

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92 XLT and '87 Bronco II
Good point. For some reason I thought it was a '94. A '91 should be outputting 2 digit codes, only has one O2 sensor (your code list gives codes for two O2 sensors), and doesn't have an EGR system. Any possibility someone swapped a '93/'94 computer into the truck?
 




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