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P0491 and P0492 secondary air injection codes

Jeremy Cottrell
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Ed T Member

Ed T

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Posted (edited)

2004 C4S,Cab. My tech repaired a vacuum leak recently.  All was good, but now have 491 and 492 codes.  The 40 Amp fuse is intact.  I still have some more troubleshooting to do.  Can I damage the engine by driving with these codes?  

Edited by Ed T
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Loren Member

Loren

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43 minutes ago, Ed T said:

2004 C4S,Cab. My tech repaired a vacuum leak recently.  All was good, but now have 491 and 492 codes.  The 40 Amp fuse is intact.  I still have some more troubleshooting to do.  Can I damage the engine by driving with these codes?  

 

Not likely engine damage.

A flashing CEL indicates potential engine damage and/or cat damage.

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Ed T Member

Ed T

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Hi All, 491, 492 codes.  I checked the Fuse, checked the secondary air pump, replaced the MAF & all 4 O2 sensors.  

 

After all of the above I got a 153 code today.  

 

Loren I've seen your multiple posts re: the 1st codes and troubleshooting.  Am I missing something?  Barking up the wrong tree?

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JFP in PA Member

JFP in PA

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36 minutes ago, Ed T said:

Hi All, 491, 492 codes.  I checked the Fuse, checked the secondary air pump, replaced the MAF & all 4 O2 sensors.  

 

After all of the above I got a 153 code today.  

 

Loren I've seen your multiple posts re: the 1st codes and troubleshooting.  Am I missing something?  Barking up the wrong tree?

What do the voltage traces for the O2 sensors before and after the cats look like on bank #2? Whose O2 sensors did you install?

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JFP in PA Member

JFP in PA

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5 minutes ago, Ed T said:

I haven't checked the voltage before and after the cats.  They are all Bosch O2 sensors.  I noticed the post cats are actually in the downwind end of the Cat.  

You need to look at the voltages; the ones ahead of the cats should cycle very quickly in a sine wave fashion, the one behind the cat should be relatively steady.  If the one ahead of the cat is cycling slowly, or not at all, it is showing age out condition's.

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