New X-pipe-P0156, P0174 codes

[bbayne35]

I have a 2000 GT. I installed a Bassani catback exhaust and Bassani X-pipe about 10 years ago along with some MIL eliminators soldered into the rear O2 sensor harnesses. I needed to replace the X-pipe due to a rattling sound possibly caused by a small slit in the heat shield area. I replaced it this weekend with a new Bassani Catted X-pipe. I replaced the original front O2 sensors as well. I reinstalled the old rear O2 sensors since they have the MIL eliminators. After a few days of driving, I saw a P0156 code (O2 Sensor Circuit malfunction, Bank 2, Sensor 2). Bank 2 is the driver side, right? Sensor 2 is the rear, right? I rechecked the rear driver side O2 sensor, reconnected it and cleared the code. After a few drives, the light came back on with P0156 and P0174 (Too Lean Bank 2) codes.

I was originally thinking that I may have damaged the rear O2 sensor during uninstall from the old x-pipe and re-install into the new. So, I was going to replace both rears, but the P0174 code is making me wonder if something else is going on.

On a side note, I seem to recall my original x-pipe was an "off-road" version, as evidenced by the fact that I saw no signs of any substrate inside of the "catalytic converter" portion of the old x-pipe. It apparently was designed to look like it had cats even though it really did not. The new x-pipe really does have cats. Is it possible that the MIL eliminators are no longer needed and are causing the problem?

Any insight is appreciated. Thanks!

 

[wmburns]

Bank 2 sensor 2 is the left rear O2 sensor.

FWIIW, anytime the DTC code calls out a "circuit malfunction", focus first on a wiring fault.

However, if asked to handicap this thread, my vote is an exhaust leak allowing unmetered air to enter. The air is making the PCM "think" the motor is lean. Especially since a new exhaust system was installed.

Focus on the left side (driver's). Check the EGR system for leaks.

Of couse an intake vacuum leak can cause this as well.

>>
P0174 - System to Lean (Bank 2)


Air Measurement System
MAF sensor (contaminated, damaged, malfunctioning, etc.)

Fuel System
Fuel pressure regulator (leaking, malfunctioning, etc.).
Fuel filter plugged, dirty.
Fuel pump (weak, check valve leaking, etc.).
Leaking/contaminated fuel injectors.
Low fuel pressure or running out of fuel.
EVAP canister purge valve leaking (when canister is "clean").
Fuel supply line restricted.
Fuel rail pressure sensor (incorrect reading).

Air Induction System
Air leaks after the MAF.
Vacuum leaks.
PCV system (leak, valve stuck open, etc.)
Improperly seated engine oil dipstick.
Air induction turbulence due to incorrect air filter.

Exhaust System
Exhaust leaks before or near the HO2Ss (exhaust manifold gasket, mating gaskets, etc.).

EGR System
EGR valve tube/gasket leak
EVR solenoid vacuum leak

Secondary Air Injection
Damaged/malfunctioning secondary air injection system (mechanically stuck valve).

 

[bbayne35]

I will re-tighten the nuts at the driver's side header to x-pipe joint. I know that I tightened them to the proper torque value, but maybe they came a little loose or require more tightening. Given that the problem only seems to be on Bank 2, I agree with you that there may be an exhaust leak at that joint.

Do you agree that the MIL eliminators are NOT causing a problem? I am guessing they are fine since I am not getting a Bank 1 DTC.

I did log data on my Predator on my 30 minute drive home from work yesterday. The rear driver side O2 sensor seemed very low. It ranged from 0 to .09 V with an average of about .05 V. The rear passenger side sensor ranged from 0 to 0.55 V with an average of about .15 V.

This new x-pipe is a 5 piece design. In other words, the cats are not welded in place; hefty band clamps are used instead. I tightened the crap out of the clamps, but I may be able to get a few more turns on those as well.

 

[wmburns]

I'm not sure why you are focusing on what the rear O2 sensors are doing. You should be focusing on what the front O2 sensors are doing. The front O2's affect driveability.

Yes I absolutely agree that the rear O2 sensors are NOT the problem.

Besides, the data values from the rear O2's are always going to show crap values when MIL's have been installed. That is how MIL's work.

I can image that if there is an exhaust leak, that you can't hear it. Tighten something that was correctly torqued in the first place does not seem wise to me unless there is a known active leak.

Try spraying soapy water solution on the exhaust joints and look for bubbles. This might work best while the exhaust is cold.

 

[bbayne35]

My concern with the rear sensors are the MIL eliminators. If I understand correctly, in an off-road set-up, there are no cats to burn excess fuel, so the rear O2s sense a rich condition and throw a code. The MIL eliminators filter that signal and send an acceptable value back to the PCM. If I now have cats, maybe the adjusted signal is too low and causing the P0156 code?

Regardless, this morning, I put the rear wheels on ramps. When I started it, I noticed some water dripping where the cats are clamped to the x-pipe. I assume this is from condensation, but the drips were telling me that those clamps may not be tight enough. I actually noticed more dripping from the passenger side. I loosened the clamps, moved them a little, and tightened them again. I checked the nuts on the driver side at the x-pipe/header joint, and they seem to be tight.

I sprayed soapy water and did not notice much, but the cats heated up so quickly that the water was evaporating and preventing me from getting much of an evaluation. I could not hear any exhaust leak (what would it sound like?). The car actually feels and sounds like it is running ok.

So, focusing on the P0174 possible causes. The MAF sensor was cleaned recently. I installed a new fuel pump and filter a few months ago. I did remove the stock injectors about a month ago to install new Accels. I had issues with the Accels and re-installed the stock ones. The car is running fine with the stock ones, and I have not yet received any misfire codes. Air induction seems to be ok. I would assume a vacuum leak would cause a lean condition in both banks. What can you tell me about the EVAP canister purge valve? Is this a common part that fails? Would that also cause a lean condition in both banks? Is the exhaust manifold gasket something that commonly fails over time? I still have the stock headers on my car.

 

[SteedaGT9150]

An exhaust leak will sound like a ticking noise, as the rpm's increase the loudness and speed of the tick will increase.

Also, you do not need MIL's if you are running a catted x pipe.

 

[wmburns]

I would assume a vacuum leak would cause a lean condition in both banks.

This is NOT correct. There are some vacuum leaks that will throw a DTC code only on one side.

Consider that a valve cover leak, or an intake manifold leak directly above a cylinder will affect the closest bank.

IMO, the fact that water leaks from the exhaust is NORMAL. In fact, if the exhaust were water tight, this could create a blockage. Remember that exhaust leaks after the O2 sensors don't affect their operation.

 

[bbayne35]

The information is appreciated.

So, after I moved the clamps and re-tightened them as I stated in my last post, I did see the P0156 code the next time I drove the car. I have been monitoring the O2 sensor data as I have been driving for the past few days, and the rear driver side O2 sensor voltage is remaining low (below .1V). All of the others are switching back and forth in what appears to be a normal manner. So far, I have not gotten the lean code P0174. When I started my car this morning, the CEL went off. I checked with my Predator, and P0156 is still present (I assume it would be until I clear it). Why would the light go off? I will monitor that same rear O2 sensor again on my way home. It seems to me that the rear driver side O2 sensor may be faulty. At this point, should I try replacing it?

 

[bbayne35]

Just to follow up on this...

My Service Engine Soon light was continuing to go on and off for a couple of weeks with a P0156 code. I ordered new rear O2 sensors and installed them today. The rear driver's side sensor (which was throwing the code) seems to have failed. It rattles when I shake it, and I can see a small ball moving around inside. The new ones do not rattle. I installed the new ones and monitored their voltage for a few minutes. Bank 2 sensor 2 still seems to be lower than the others, but it now will occasionally flucuate above .1 V. Hopefully, the problem is solved. I will continue to monitor it and post if I discover anything else.