O2 Sensor Hell

[AndyA]

This is such an annoying problem that has been plaguing me for over a year. I managed to get it through emissions in the narrow window between reconnecting the battery and getting all the emissions monitors ready and before the CEL coming on. The CEL finally came on about half an hour after the emissions test. Phew.

Code is P0133 - O2 sensor slow response bank 1 sensor 1. It is intermittent - went away for several months after changing the O2 sensors then came back.

I have replaced all of the O2 sensors with NTK replacements.

The connector is secure and the contacts are not corroded.

The PCM is a Wanglerfix unit.

I've connected a leaf blower to the exhaust and sprayed soapy water and I didn't see any bubbles as best as I could see.

So I think this narrows it down to:

- bad sensor even though it is new
- PCM problem?
- CAT problem
- loose manifold bolts

I am so fed up with this. My next step is to try swapping the upper O2 sensors and see if the error follows the sensor or not. I am 80% sure I already tried this a year ago and it stayed at the 1/1 location but I will try again.

I generally don't like throwing money at problems, I prefer to diagnose and replace the correct part, so I am hesitant to replace the cats if I don't have to.

I cannot see the manifold bolts or really much of the exhaust manifold. I am not confident I sprayed much of it with soapy water. Is there a better way to look for leaks on this particular engine with the intake manifold right above the exhaust manifold?

Thanks Andy

 

[macleanflood]

You need to monitor live ODB data and the O2 sensor voltage. They should range below .9v.

You can do this with the free Torque Lite app and a $30 Bluetooth ODB dongle.

Without hard data you can't make a proper diagnosis and everything else would be speculation.

-Mac

 

[AndyA]

Thanks Mac. Is this to diagnose if it is the sensor itself vs something else or can it tell me what else might be the issue? I know that the O2 sensors switch voltages between low and high but what am I looking for in the data?

Thanks, Andy

 

[macleanflood]

For starters that the voltage ranges below .9v.

-Mac

 

[Chris]

Not to be obtuse, but have you made 100% certain it's not a wiring harness issue?

 

[ItchyDong]

- bad sensor even though it is new
- PCM problem?
- CAT problem
- loose manifold bolts

-Bad sensor, maybe. It’s been known to happen.
-PCM. Probably not
-CAT, probably not. Most of the time a bad CAT is driven by the downstream sensor “copying” the upstream sensor and will set an efficiency code.
-Loose Manifold, probably not.

You need to graph some live data like MAC said. Look at the offending O2 sensors activity compared to the opposite banks upstream sensor. Stress test the sensors by adding an alternative fuel source (propane, brake parts cleaner, snap throttle) and see if you can force the sensor to read rich. Then introduce a lean condition by inducing a vacuum leak and see if the sensor is able to drive lean.

If neither of those tests are fruitful, it points to a bad sensor, however, wiring checks would be in order before I would sell a sensor to a customer. You can unplug the sensor and force a fake rich condition with a test light from battery positive while monitoring live data, and the same with a test light to ground to simulate a lean. This verifies wiring integrity and the PCM’s ability to correctly interpret the data.

 

[JKP]

Check the cat to manifold bolts, they loosen up. I've had to tighten mine several times.

Look straight up from under the Jeep, 4 15mm bolts. If you can wiggle the cats, they are loose.

Somebody recently had a leak there even though the bolts were rusted in place, broke them free then tightened.

 

[AndyA]

OK Thanks. I have ordered a bluetooth OBDII gizmo so I can do the charting. Andy

 

[Hacker412]

On mine, the PO broke the Po2 connection. I did not know the guy, but I bet money he is not an electrician. I replaced and rewired it, and no more check engine light

 

[steelhd]

So I think this narrows it down to:

- bad sensor even though it is new
- PCM problem?
- CAT problem
- loose manifold bolts

I am so fed up with this. My next step is to try swapping the upper O2 sensors and see if the error follows the sensor or not. I am 80% sure I already tried this a year ago and it stayed at the 1/1 location but I will try again.

I generally don't like throwing money at problems, I prefer to diagnose and replace the correct part, so I am hesitant to replace the cats if I don't have to.

I cannot see the manifold bolts or really much of the exhaust manifold. I am not confident I sprayed much of it with soapy water. Is there a better way to look for leaks on this particular engine with the intake manifold right above the exhaust manifold?

Thanks Andy

That is a lot of work. I recommend uprooting the family and moving everyone and everything you own to a state without emissions testing. <waves hands> Solved!

 

[AndyA]

I disconnected the battery and did some electrical testing on the O2 1/1 harness connector:

Solid connection from ground pin to ground.
Solid connection from signal pin to PCM S2 connector
Solid connection from signal return pin to PCM S1 connector.

Solid means jiggling the engine wiring harness at multiple points along it did not interrupt the connection.

I tested the O2 1/1 sensor connector:

Heater coil was 4.0 Ohms.
No connection (electrically open) between signal, ground and signal return (same on O2 2/1 sensor) pins.
No connection between ground pin and ground of vehicle (so not grounded through body of sensor).

The pre-cats are solidly bolted to the exhaust manifold.

The O2 1/1 sensor is securely bolted into the pre-cat manifold.

I reconnected the battery and CEL was now off, I presume from the disconnect. I did about 30 miles of driving including some Interstate and no CEL. Connecting my reader shows no stored or pending codes.

I then captured the O2 1/1 voltage, the O2 1/2 voltage and the O2 2/1 voltage (for comparison). I have no idea how to interpret these. The final image is zoomed in a bit compared to the other two.

All four O2 sensors were replaced at the same time with NTK.

Thanks! Andy

 

[macleanflood]

I see voltage ranging over .9v. While not definitive it's indicative of a bad O2.

-Mac

 

[AndyA]

Thanks. What do you make of the other upstream sensor? I am not getting any error codes for that but the waveform is all over the place. Andy

 

[InOmaha]

I replaced my O2 sensors and got a noticable performance upgrade on the low end. But threw a code a last week after 6 months code free. So I'm watching the thread. Same sensor code as before P0153.

It was after filling the tank and a cold start stumble after starting in a parking lot later. I cleared it and there's been nothing for a week.

 

[TJ Jim]

Just for a comparison for you @AndyA on my Jeep. This is after I replaced mine for a heater circuit fault.

 

[AndyA]

Thanks that is very helpful. Can I conclude from my data that the bank 1 precat is working fine. Seems to be storing oxygen?

Andy

 

[AndyA]

Replaced the 1/1 O2 sensor with another NTK sensor and I still have voltages going above 0.9V. Any ideas what to try next? Thanks, Andy

 

[macleanflood]

Interesting. I replaced my rear O2 on my 97 with a Walker...did the same thing and trended above .9v...then a new NGK...same issue...then I grabbed a used NGK off a 2001 and it works perfectly.

New parts suck.

-Mac

 

[AndyA]

Did you get DTCs with both of those sensors? Maybe going above 0.9V is not really an issue? Or maybe the engine is running too rich because of an unrelated issue?

Andy

 

[Chris]

New parts suck indeed. Just like every other aspect of life that is slowly getting worse, such is the case with replacement parts.