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Old 03-12-2011, 12:12 AM   #2
TENGRAM
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Join Date: Mar 2006
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an aside from Joel5.0:

Quote:
Every now and then I read or hear customers saying..."there are no failure codes, since the CEL isn't turning on while driving, there shouldn't be any codes".......although that observation is true for most OBD-II systems, it's NOT TRUE for EEC-IV or Ford's OBD-I systems. This means that the possibility of having a failure code present causing driveability problems w/out having the CEL indicator at the instrument panel on, is not only true, but common. This is one of the reasons why the only reliable way to check EEC-IV systems is by running the system self-test routines described in the previous post.

FYI....the following failures or codes are the only ones that would trigger the CEL/MIL to turn on for the time the failure condition is present, once the failure is not present, the CEL will turn off:

CIRCUIT CODES
ACT 54, 64
ECT 51, 61
BP/MAP 22
MAF 26, 56, 66
TPS 23, 53, 63
EVP 31, 32, 34, 35
HEGO(1) 41, 91, 42, 92
(1) Based on a "lean-rich" switching counter timer function.

Intermittent codes will only trigger the CEL during the time the failure condition is present. Any other circuit failures may be present, affecting driveability and/or performance, but not cause the CEL to turn on....and can only be identified/retrieved via the self-test routines. Another case are the failures that are not logged in memory, but are present during engine operation.....any failure code that doesn't have a "M" = memory, continuous notation, but any of the others, falls under that category...


What happens when the CEL is on?........the EEC-IV uses a variant of a Failure Modes Effect Management (FMEM) strategy to compensate for the failures...or as described by Ford.....

The Failure Mode (FMEM) strategy protects vehicle function from adverse effects of an EEC component failure. The strategy recognizes open or short circuit failure for six sensors: MAF, TP, ECT, ACT EVP/EPT, and BP. In general, if the continuous Self-Test strategy recognizes a failure the FMEM strategy will execute an alternative vehicle strategy. The alternative strategy disables logic which relies on realistic sensor values. Some sensor FMEM strategies also substitute a "safe" value for the bad sensor.

What are those strategies?.....check the table below, look at the column of the failing sensor, and check the alternative actions it does....



Bottom line.....

Just because you don't see the CEL turning on, you may have circuit failures that affect EEC-IV functionality and performance, run the damn self-tests ....it will provide you with the information you need to correct any problems w/out having to replace unnecessary components, and throw away hard earned

Last edited by TENGRAM; 03-12-2011 at 12:28 AM.
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