Advice please. I have a 98 C5 coupe auto, 135,000 miles. I'm getting these two codes with the check engine light and it is running rough at idle.

P0151 Heated Oxygen sensor (H02S) Circuit low voltage Bank 2 Sensor 1

P0174 Fuel Trim System Lean Bank 2

I looked for vacuum leaks visually and all looks well. I would think if a vacuum leak was the problem, both sides would be lean? I pulled the plugs and sure enough the drivers side is chalky white and the passenger side is black, so it is lean on that side for sure, pict below.

Should I go ahead and replace the Bank 2 sensor 1? If so is this the one on the header, drivers side? I already check power and ground on this sensor. Should I check something else before this is done or could it be anything else?

Thank you everyone!

 

If you want the quick fix 99% of the time if you have a heater circuit code it needs to be replaced. Bank 2 Sensor 1 is the front sensor on the passenger side. Replace it, clear codes and drive to see if the lean code comes back. You said headers in your initial post so just check that the wiring did not come into contact with a header tube and melt it.

 

If the plug with the soot on it is from the right bank, replace the primary o2. It's lying, telling the PCM it's lean when it isn't. That's why it's rough idling and fouling plugs. Here is a description of the code.

The PCM supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The PCM monitors and stores the Heated Oxygen Sensor (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed below a predetermined voltage. If the PCM detects the voltage is below a predetermined voltage, a DTC sets.

CONDITIONS FOR RUNNING THE DTC
DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0125, P0200, P0335, P0336, P0351-P0358, P1120, P1220, P1221, P1258 are not set.
The ignition voltage is greater than 9.0 volts .
The fuel system is operating in Closed Loop.
The AIR and the Catalyst diagnostics are not active.
The TP angle is between 2 percent and 70 percent.
CONDITIONS FOR SETTING THE DTC
The HO2S signal voltage remains below 200 mV .
The conditions are present for 31 seconds .
ACTION TAKEN WHEN THE DTC SETS
The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

At 135k I wiould replace both primary sensors and install a fresh set of plugs. You'll be good to go!

 

Really needed this input and can't thank you enough. The black plug is from the passenger side, so that upstream heated O2 sensor will be swapped out Monday. I was being a bone head and thinking lean, so I thought the white plug from the drivers side was the problem. Sanity check, well I guess I failed, but win never the less with this advice.

I'll post with the results.

 

It may be the camera angle, but aren't those plug gaps a bit wide as well?

 

I thought so too, but they are already in the landfill. These were the original plugs and their first time out as far as I know.

 

I just went and put an eye ball on it and I'm wondering if the way to get it is from the top, perhaps if I remove the battery and the plastic box around the battery compartment?

 

You mean the 02's sensor ? You did say you headers correct ?

 

In either case no you change them from underneath and access the connector from there also. With headers the PS is a breeze. The DS with (my Kooks LT's) is a little more difficult.

 

Whoops, it is all stock, so exhaust manifold? Picked up "a" sensor at AutoZone, Bosh. Not looking for more trouble, time and financial loss. I did change the plugs and wires, yesterday. Thanks for the input. Tomorrow is the day, will post results......

PS, just two weeks ago she left me stranded with a broken auto shift cable.

 

She Purrrrrrrrrrrs.......... like a kitten. I was so pumped, I reaplaced all four sway bar links, turned the rotors, new pads and shocks all the way around that I purchased form someone on this very board a few years ago. Can't thank everyone enough for the help.