getting check engine light

Quote from jpfan

as stated above getting check engine light did the key test and pulled an error code 51 says lean condition check o2 sensor/ which one upsteam or downstream and how can you tell which is the culprit

P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)

If there are only 2 it would be upstream I believe.

what engine are we dealing with

Quote from Keith_C

P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)

If there are only 2 it would be upstream I believe.

The only thing that sounds odd with that is the bank 2 part, I know most codes systems are set up where with a V style motor one side (Being the side with cylinder 1) is Bank one, and bank two as the other side. but being that we are talking about a strait 6, Bank two is odd, unless Jeep did it differently. Since It says sensor 1 I would think it would be the upsteam sensor, the one before the cat. They are usually numbered from the engine back.

Quote from BigRed

The only thing that sounds odd with that is the bank 2 part, I know most codes systems are set up where with a V style motor one side (Being the side with cylinder 1) is Bank one, and bank two as the other side. but being that we are talking about a strait 6, Bank two is odd, unless Jeep did it differently. Since It says sensor 1 I would think it would be the upsteam sensor, the one before the cat. They are usually numbered from the engine back.

Not odd at all, that's how the I6 is handled.

1-3 are bank one, 4-6 are bank 2.

My '03 has 4 O2 sensors, and they are know as bank 1 sensor 1 & 2, bank 2 sensor 1 & 2.

I looked up some stuff, and i now see how that works, with the newer 4.0's. With mine all 6 cylenders are run through the same manifold, like this.

It seems that the newer ones split the job of the manifold, like this.

I never knew that, I guess ya learn something new everyday.

But from what I can tell the 97 4.0 still uses a manifold like mine where it is all one piece. Thats where my confusion comes in with the Bank 2 part.

97 4.0 Jeep Wrangler Exhaust manifold ( According to Autozone.com)

Quote from BigRed

It seems that the newer ones split the job of the manifold, like this.

Yeah since there was so much trouble with them cracking they went to a 2 pc design, not sure when.

Quote from Keith_C

Yeah since there was so much trouble with them cracking they went to a 2 pc design, not sure when.

Thats a good idea on there part, I have heard of there being lots of problems with that. Thanks for the help there.

jpfan

As far as we can tell I think we both agree that the Upstream is whats giving you your problem. Most likely the O2 sensor is your problem but there is still a chance that it could be a wiring issue or the o2 sensor heater circuit. If I had to bet I would just swap out the o2 sensor, After checking the wiring for any visible problems that could give the PCM a low voltage signal.

Good luck to ya

Andy

how many miles on your engine? have any O2 sensors been already replaced?

just replace them all. it costs a few bucks, but it'll save you from spending a lot of time trying to figure out which it is. and on a '97, this might not be the only one that goes bad on you. one went bad, and there are three others, any of which could go at any time due to the age and milage. so replacing them all might also save you from having to do this again.

i did all four of mine last year.