My 2008 H3 has had a P0420 since I bought it. I never worried too much about it since the Previous owner told me that he had recently replaced the Cat with an aftermarket one. I figured that either it would eventually go away as the Cat got some time on it, or -- Well, there are other things I can do about it -- one being just live with it.

But every time I connect my SCAN Tool, there are more codes.

A few months ago I noticed I also have a P0014.

The vehicle does have a rough idle, but not bad.... I know about cleaning the throttle body/etc. I always figured I'd "Get a round to it" someday. It actually seemed to get better after an oil change -- it's barely noticeable over a "normal car" once warmed up.

But a few days ago, it developed a really bad idle from a cold start, and the next day, it did the same thing, and then actually quit in my driveway. I started it back up, and it ran fine the rest of the day, but I figured I'd better put the SCAN tool on it again.

Now add to the list a P0300. I watched with the scan tool, with the engine idling in the driveway, and saw various misfires on all cylinders, but mostly Cylinder 3.

The oil (as mentioned) was recently changed and the drained oil looked fine. I paid particular attention to it due to the high mileage (almost 142K miles at the time of the oil change. The oil on the dipstick now still looks fine.

My current plan is to just throw parts at it -- I have no problem doing this since it is an older vehicle, and I don't know it's history.

I am going to buy a cam position solenoid, and 5 plugs. I'll clean the TB when I have the intake box off to get to the plugs.

The other codes that suddenly popped up are all of the O2 Sensor Heater Codes.
P0030-00
P0036-00
P0053-00
P0054-00
P0135-00
P0141-00
P0420

Since the O2 Sensor heater voltage is not one of them, and from getting the same groups of codes on other vehicles, I am going with the fact that both upstream and down stream O2 sensors need to be replaced. Again, given the vehicles age, mileage, and history I don't mind throwing even O2 sensors at it. It just may fix my P0420, too.

So I have a plan, but if anyone has other suggestions, warnings, etc., I would appreciate it.

 

Clear codes & recheck after running to operating temperature.

 

Your P0420 and all the various Oxygen Sensor codes could be related, as bad O2 sensors can potentially trigger a P0420 code. As pointed out, clear everything, and see what the car throws at you once up to operating temperature. Make sure your oxygen sensor connectors (and wires that are not protected with heat shrink, etc.) are not too close to the hot exhaust pipe; I got a false reading from one of my sensors (and a CEL code) in the past due to the connector being misplaced right next to the hot exhaust manifold. Once I repositioned the connector and reset the codes, the code has not reappeared.

Regarding the misfire codes, lots of things could be causing this. Definitely start with the easy things, such as inspecting the spark plugs and cleaning the throttle body, but do not start throwing parts at the problem.

If the plugs need replaced, then replace them. If the throttle body needs cleaned, clean it. Do this and see what happens. Since you have the plugs out at this point, I would personally take it a step further and run a compression test and measure the psi.

If the compressions are all around 175 psi or greater, then this is probably not the reason for your misfires.

If your compressions are more in the 150-160 psi range, this can certainly trigger misfires and codes. From here, you need to figure out the source of the low compression (intake valves, exhaust valves, piston rings, or head gasket) which can be accomplished via a leak down test.

If the source of the leakage is the valves not sealing, then this could be carbon buildup on the valves, causing them not to seal properly. Running some Seafoam through the engine can help remove the carbon; Hummerz has a great setup for how to do this.

The P0014 has to do with exhaust camshaft timing for the variable valve timing system. If your exhaust camshaft phaser is not operating properly, this can cause this code. Other things that could trigger this are a bad exhaust camshaft sensor, and also a bad VVT solenoid, or worst case, if the timing chain has jumped a gear.

I would definitely start with checking the spark plugs, running a compression test, and cleaning the throttle body. In this engine, a dirty throttle body can absolutely cause your engine to do stumble and stall out (at least it did on mine years ago); do not underestimate just how much a throttle body cleaning can improve your performance.

 

MILES on the truck????????????????

 

" almost 142K miles at the time of the oil change. The oil on the dipstick now still looks fine. "

 

Sorry -- 142K Miles.