Check Engine light

PaulS said:
It's a test that monitors the switching of the 2nd o2 sensor. Could be a leaking injector or an air leak. I'm telling you, for me the issue was the PCV valve not closing properly allowing extra air in beyond the MAP sensor in my Grand Cherokee. It caused a P013C code, o2 sensor 2/2 slow to respond. But it also caused the P0430 code, though not as often. Were I faced with a cat issue again, it's the first thing I'd replace. These issues start out slow, you get a few thousand between mil trips, then it goes down to a hundred miles. I would also check the EGR valve and tube. The valves can stick after a while, there's a parameter you can watch on the scanner to see the lag if you have one, at least there was for the Hemi. Doesn't set a code.
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You mean MAF sensor, right?

There is no way to let air "past" a MAP sensor, except perhaps through an exhaust valve or head gasket breach (not very likely), or a broken vacuum line that disconnects the sensor from the manifold (more common). It measures pressure in the intake manifold.

MAF sensors can be bypassed rather easily by vacuum leaks of any sort. But it's a little weird for a PCV valve to make an internal vacuum leak -- usually, they draw ambient air from the intake tube in front of the throttle, which still goes through the MAF (that way, you are still using filtered air!). However, they can leak around the outside and get unmetered air that way. And if the valve cover is also leaking, that might explain it.

Lots of stuff can cause the downstream sensor test to fault. Vacuum or fuel leaks sufficient to overpower adaptivity will certainly do it, but so will exhaust leaks ahead of the cat -- it will never run the reduction cycle and run cool, making it ineffective. Just an old or fouled sensor might be enough, or damaged wiring. Poor grounding at the PCM or body can make for all kinds of really interesting faults, including this one (seen it on a Camry).

The big one is that engine basics have to be decent before the self tests are reliable. Pretty much anything that cools the exhaust is going to present problems for the cat. They like it hot. To a lesser extent, so do the HEGO sensors; they will read lean below 600 deg no matter what is going on. Retarded spark timing is a common problem here. So is a blown head gasket.
 
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MAKG1 said:
You mean MAF sensor, right?

There is no way to let air "past" a MAP sensor, except perhaps through an exhaust valve or head gasket breach (not very likely), or a broken vacuum line that disconnects the sensor from the manifold (more common). It measures pressure in the intake manifold.

MAF sensors can be bypassed rather easily by vacuum leaks of any sort. But it's a little weird for a PCV valve to make an internal vacuum leak -- usually, they draw ambient air from the intake tube in front of the throttle, which still goes through the MAF (that way, you are still using filtered air!). However, they can leak around the outside and get unmetered air that way. And if the valve cover is also leaking, that might explain it.

Lots of stuff can cause the downstream sensor test to fault. Vacuum or fuel leaks sufficient to overpower adaptivity will certainly do it, but so will exhaust leaks ahead of the cat -- it will never run the reduction cycle and run cool, making it ineffective. Just an old or fouled sensor might be enough, or damaged wiring. Poor grounding at the PCM or body can make for all kinds of really interesting faults, including this one (seen it on a Camry).

The big one is that engine basics have to be decent before the self tests are reliable. Pretty much anything that cools the exhaust is going to present problems for the cat. They like it hot. To a lesser extent, so do the HEGO sensors; they will read lean below 600 deg no matter what is going on. Retarded spark timing is a common problem here. So is a blown head gasket.
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There is no MAF on a hemi, at least 2008.
 
MAKG1 said:
Not enough.

Here is an example of a Jeep (Cherokee) drive cycle:

http://www.smogtips.com/smog-question/2839/Jeep-Cherokee-Emission-Monitors-Not-Ready

Here's the relevant monitor:


Did you do all that in your 60 mile drive, or did you fill the tank and drive for an hour at highway speed, and then park?

Even if you did, you need to connect a scan tool to see if the monitor actually ran, before assuming your MIL is fine. If it wasn't run for any reason (including an unrelated fault -- not all potential faults set DTCs, and even those that do sit in a "pending" state for at least a drive cycle), your test is inconclusive.
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It is not a Cherokee, and my maintenance manual has no such test.
checked the error codes this evening after another 40 mile drive and there are no stored codes.
the light is still out.
 
Tom-D said:
It is not a Cherokee, and my maintenance manual has no such test.
checked the error codes this evening after another 40 mile drive and there are no stored codes.
the light is still out.
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100 miles should be good, some of the tests need highway speed. Hopefully you won't see it again.
 
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