Check engine light diagnosis.

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Nov 30, 2014 | 02:25 PM

wakum6

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Joined: Jan 2014

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Check engine light diagnosis.

So I've been getting a check engine light every once in awhile on my 94 F150 5.0. I ran a engine off key on test and got 3 codes:
176 Oxygen sensor not switching- system is/was lean left or front oxygen sensor.
177 Oxygen sensor not switching- system is/was rich left or front oxygen sensor.
327 EGR feedback signal is/was low.
The first 2 seem connected since they're completely conflicting codes but I don't know where to start troubleshooting. The EGR I have no idea about. I recently replaced the EGR sensor so maybe the EGR itself is bad? Also I'm thinking the cold weather may have some sort of effect on at least one of these issues. The CEL only used to come on intermittently in the early morning then go away. Now with temps below freezing it'll come on and stay on. Any advice?

Nov 30, 2014 | 06:02 PM

rla2005

Fleet Owner

Joined: Oct 2005

Posts: 20,786

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From: Kentucky

Codes 176 and 177 are only from historical (CM) memory. Code 327 can be displayed during the KOEO tests, CM display or KOER tests. I suspect you read it during the CM display.

Clear the codes then drive the truck again. See if any of the codes return. If they do, check for codes then list them here by number and when they were displayed.