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JLS 03-10-2010 11:42 AM

Check Engine light - lean/rich
I have a 97 TJ, 2.5l that the check engine light came on. Trouble code showed lean & rich state - replace the O2 sensor with a bosch. Light stayed off for 3 days and came back on. I can reset it, but it comes back. I have gotten a new gas cap, new plugs wires and still no help. Gas mileage has gone from roughly 16 mpg to 9 mpg. Any ideas from anyone???

jwm1986 03-10-2010 02:41 PM

Sticky fuel injector, sticking valves, failing catalytic convertor... That's about all that comes to mind for that kind of stuff. Other than what you've already done.

Jerry Bransford 03-10-2010 02:47 PM

Where was the 02 sensor you replaced, on the exhaust manifold output pipe or on the cat?

JLS 03-10-2010 03:21 PM

It was at the junction of the exhaust manifold and the exhaust system. There is only one O2 sensor.

JLS 03-10-2010 03:22 PM

Anyway to isolate which one of the three could be causing it without replacing everything?

Gonda 03-10-2010 03:51 PM

It could be an exhaust leak upstream of the O2 sensor. This will make the O2 sensor think the engine is running lean and so it will compensate by telling the ECU to add more fuel.

Gonda 03-10-2010 03:54 PM

Also, I would pull all the plugs and see what they look like.

Do you hear any misfire?

A compression check should eliminate the possibility of a valve.

rrich 03-10-2010 04:17 PM

What specifically was the code the first time, and is it still the same?

Your interpretation of the code isn't clear.

JLS 03-10-2010 09:01 PM

Engine backfired prior to replacing O2 sensor, and just started again 2 weeks after replacing it. The trouble code was a 51 & 52, and I amstill getting the same codes now.

01bud 03-10-2010 10:38 PM

how many miles on motor ? check timing

rrich 03-10-2010 11:32 PM

P0051, P0052

Both codes indicate it's a problem with the O2's heater circuit. Check the wiring to the sensor. It runs close to the exhaust pipe, it can melt through to it, grounding the heater wire to the sensor. It's the harness side back from the pigtail on the new sensor.

And - note the article also suggests using one from the dealer since aftermarket sensors are often ”one size fits all.”

P0051 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1) - DTC Code

P0052 Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1) - DTC Code

I've found quite a few times that using one from a parts house gives trouble - especially if its Bosch.

Check the wiring to the heater first. Disconnect the sensor, then key on find which wire at the connector (not the sensor) has 12 volts on it. Follow that wire back up.

s3nt3nc3d 03-10-2010 11:53 PM


Originally Posted by rrich (Post 568287)
I've found quite a few times that using one from a parts house gives trouble - especially if its Bosch.

I'm not sure if Chrysler uses the same supplier for the Wrangler O2 sensors...but NGK was the supplier of O2 sensors for my old 98 Dakota. And buying straight from NGK was much cheaper than buying O2 sensors from the dealer.

I'll 2nd the fact that certain aftermarket sensors don't function identically to the original sensors... TPS sensors are another good example of sensors you should purchase from the dealer.

rrich 03-11-2010 12:09 AM

Also check ALL the fuses - probably not that, but check anyway.

It's probably intermittent, shorted then not, that's why you have both codes, lo and high.

.For the 5 to 10% in savings, it saves you hours of troubles if you buy quality first.

Let us know.

Bosch - Hitler's revenge!

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