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

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Edmunds Insurance Estimator

The Edmunds TCO® estimated monthly insurance payment for a 2012 Jeep Wrangler in WA is:

$176 per month*
* Explanation