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2003 Jeep Wrangler O2 sensor issue

02-03-2010, 01:34 AM
A friend of mine has a 2003 Jeep Wrangler X with the 4.0L I6 and an automatic transmission. It was throwing code P0155 for Bank 2 Sensor 1 Heater Circuit. I pulled the original sensor (136k miles) and replaced it because it was very worn out (the tip was warped and charred). The replacement was a Bosch unit from the local Advance Auto. The Bosch unit had a rounded solid tip, the original had a cylindrical tip with holes in it, if that matters. The replacement had a factory style plug on it.

I took the Jeep to my local parts store and had the code reset, but it popped up a few days later. Normally, I'd suspect a wiring issue, but the original sensor was obviously worn out. I've also found a post through google stating that the Bosch sensors have the wrong resistance for the heater and will trip the light, and another stating that Chrysler has an updated PCM flash for the O2 heater code. I checked the Wrangler forum and found nothing. I'm at a loss for what to tell my friend, other than that I will take the Jeep back and check the wiring to the O2 heater. I only found one instance of each of the above mentioned posts, but I'm not the type to simply throw parts at a problem.

In short (if you skipped the book I just typed), has anyone here heard of an issue with the Wrangler and the P0155 code? Could the coolant sensor (or some other sensor) be causing a false code? Or should I just check the harness and return the sensor if I don't find any issues?

I also reattached a braided ground strap to the intake manifold (the original bolt was gone, so I used a fuel rail bolt to secure it). Not sure if it matters, but sometimes cars are weird about things like that.

02-03-2010, 05:47 AM
Your best bet is to get a diagram and make sure there is nothing wrong with the wiring. If that passes you might have a bad sensor OR there may be an update as you mentioned. Your best bet is to take the bosch sensor back and spring for a mopar unit and see if that works out first.

02-05-2010, 12:38 AM
Since the code is for the O2 heater circuit, I would check the heater relay first. Its $6.99 and easy to try.

The best way to figure it out is to measure resistance across the high side of the relay when energized, but another quick and dirty way to test it is to swap the O2 heater relay with the air injection relay. If your O2 sensor code gets replaced with a secondary air injection code, its a no-brainer.

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