Unexpected Pentastar Cylinder Head Replacement Under Warranty - 2012 Jeep Wrangler Long-Term Road Test

2012 Jeep Wrangler Long Term Road Test

2012 Jeep Wrangler Sport: Unexpected Pentastar Cylinder Head Replacement Under Warranty

January 7, 2013

2012 Jeep Wrangler

Wow, things can sure happen fast. One moment everything's fine. It's the Sunday before Christmas and our 2012 Jeep Wrangler is running great. Late in the afternoon the check engine light comes on, but there are no symptoms other than the light itself. We're not too stressed by this because we're almost back in our driveway at home.

Turns out the closest dealer, Glendale Jeep, is closed on Christmas Eve day in addition to Christmas, so this is going to have to wait until Wednesday the 26th when they open again at 7:00 a.m. No problem. With family in town and plenty of stuff going on it's easy to leave the Jeep parked until then.

That was how it began for John Adolph. Nothing seemed too alarming, but with a 1,600-mile New Year's day road trip looming on Thursday — including a side trip for some off-road action in Death Valley — he was eager to have this handled. Besides, it was time for an oil change anyway.

John arrived bright and early Wednesday morning and told the service writer about the oil change, the check engine light and his upcoming road trip the next day. Within walking distance from home, he agreed to leave it with them, expecting to pick it up later that day.

At 10:30 a.m. he gets a call. "Yeah, you're going to need a new left cylinder head," said the service writer.

"What?" replied John, more than a little taken aback. "How much is this going to cost me?"

"Nothing. It's covered under warranty," came the reply. There was more, the gist of which was this wasn't a complete surprise to the dealer. Apparently, the need to swap in a new left-hand cylinder head isn't exactly unheard of with this new Pentastar V6.

So much so that the dealer went on to say this, "We can have you fixed up tomorrow afternoon. Do you want us to go ahead?"

For this kind of turnaround they must have had a new cylinder head very close at hand, although at this point it must be said that this Jeep brings up the name Edmunds or Edmunds.com when they put the VIN into the system. We bought it outright, but it isn't registered anonymously. Still, even with that knowledge, a one-day turnaround seems unlikely without parts standing by in a nearby depot. It probably didn't make much difference.

Whatever the circumstances, John picked up the Jeep with its new cylinder head the next day at 2:00 p.m. and was on his way. He put 1,600 miles on it over the weekend and it never once flinched. In the process, the Death Valley dirt roads applied so much fresh dust over the engine compartment that it's difficult to see signs that anything was done.

2012 Jeep Wrangler

The work ticket is clear, but it raises as many questions as answers and it doesn't explain what actually went wrong. I have a call in to Jeep to see what I can find out.

But I do know the code was P0302, which represents a misfire in cylinder #2, which is on the left-hand bank of cylinders. From there they installed a new coil, spark plug and injector, but the error code persisted.

At this point I get confused, because after this failed they did a compression and leakdown test. Knowing this is not a wholly unfamiliar issue, I'd have thought they'd do the leakdown test first before throwing any parts at it. What was the point? But I digress.

The leakdown test didn't go the way they'd hoped. The cylinder pumped up to 125 psi and exhibited 85% leakdown. I'm not privy to the actual specs for this motor, but apparently this was enough to trigger the decision to install a new cylinder head.

From the way the service writer talked about it I get the impression that the problem as it pertains to a larger set of vehicles is confined to the left-hand bank, although I don't yet know for certain. The fact that they are opting to replace the entire head tells me it may be a problem with the head itself, not a problem with a valve, seal or spring that could be repaired, but that's a guess at this point, too. And I have no idea if this is tightly confined to a small group of vehicles built with one lot of parts or something larger.

I do know that we have been sticking with Jeep's recommendation for 87-octane fuel, but we always buy that gas from top-tier name brands: Shell, Chevron, Mobil, Unocal 76, Texaco. We don't use ARCO because of their quirky payment system and their sometimes-low octane, and we don't use off brands.

Meanwhile, as far as our 2012 Jeep Wrangler is concerned, we're fine. It's running great and we love this engine just as much as we did before this went down. Maybe that's because we didn't get stranded, because we experienced no gradual decrease in performance and because we were able to react to the check engine light relatively quickly. The light came on, we went in, the dealer didn't like the reading they were getting and we got a new head with no undue hassle or delay. They had our Wrangler for a grand total of 31 hours — a day and a half to us. That they replaced something as major as a cylinder head almost seems like a dream. It doesn't seem real.

Official comment from Jeep has been requested, but we have not yet heard back. We have no idea how rare this, what causes it and if there are any measures that can be taken to avoid it. Stay tuned for further updates.

Dan Edmunds, Director of Vehicle Testing @ 24,218 miles


  • lmyers92123 lmyers92123 Posts:

    Don't sweat the head replacement. Within the Wrangler (and Pentastar) community this has been a known issue. Some valve guides and seats failed resulting in the compression loss. It is almost entirely the left head with a P302 or P206 error. The original heads were suffixed -AA and went into production through about May of last year with an -AB head short lived for a few months afterwards. Current release (that you got) would be the -AC head and I haven't heard of any -AC failures. I've had 2 heads replaced and currently have the -AC head. Most dealer are on top of this so the quick turn around is not unusual.

  • firstwagon firstwagon Posts:

    I'd sweat a bit if I still had the original heads and was nearing the end of the warranty.

  • lmyers92123 lmyers92123 Posts:

    Understandable in that scenario. It's covered under the 5 yr/100K warranty and the greatest mileage I have seen before failure was under 20K. I'm pretty sure if you have an issue it would appear before 100K. On above post I meant to type P306 not P206. Often associated with the failure is a ticking but keep in mind the injectors tick normally. It should be pretty distinct between the left and right side of the engine. You may also note some rough idling and reduced mpg's. The dealer will sometimes update the flash to try and address this but everyone I heard of always gets a new head shortly there after. Some dealers comp a rental vehicle and if you get the blank stare call customer care, ask for a case number and a vehicle. BTW, it won't leave you stranded after the check light appears. You should be able to get out of the mountains or desert and back to a dealer without a problem. All the above is based on my experience and yours may be different.

  • jku2012 jku2012 Posts:

    This is a very common issue with the new Pentastars. Seems to be worse in the Wranglers than the other vehicles. They've gone through a few head designs in the past year to correct the problem. My JKU just threw the same code this morning. Jeepers have been following the issue since it started cropping up about 1 year ago in the new 2012's. It is all over most forums.

  • jku2012 jku2012 Posts:

    I have 23,000 miles, and the first CEL came on today.

  • buff4 buff4 Posts:

    I have a 2012 jeep wrangler unlimited rubicon with 8884 miles on it. A week ago the check engine light came on and I noticed the engine seemed a bit weaker and smelled stronger than normal and it seemed that the throttle response was... well... different. I took it in to my dealer and a day later I had it back. They had found code p0300 and the misfire monitor found misfires on #2 and #6 cylinders. They performed a leak down test and found 55% in #2 and 67% in #6. They replaced the left side cylinder head and the car was running fine when I hopped into it and I will also say my milage went way up, I was getting around 11 mpg before, actually ever since I bought the car, now it's around 18. Anyways, that doesn't leave me feeling too good about my car, was planning on keeping it but now I think that is a bad idea. I look forward to hearing if anyone else has had a similar problem.

  • bessie3 bessie3 Posts:

    Just got bit by the check engine light. Took it in late last night. Today the service adviser called and said that I needed to replace the cylinder head. Unfortunately, the jeep won't be ready until 04/09/13.

  • hollywoodbb hollywoodbb Posts:

    I have 2012 Jeep Wrangler check Engine light came on, trip to dealership, need a new cylinder head. So annoyed and worried about future problems. Sounds like a lot of people are having this issue. What has jeep said about it? I am at 25,000 miles it just seems so new to be having serious issues like this.

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