I just put my stock exhaust manifolds back on after removing my long-tubes, and am getting code P0157. My search results found that the code means: HO2S Circuit Low Voltage Bank 2 Sensor 2. Is that referring to the driver side rear O2 sensor or the passenger side rear O2 sensor?

Secondly, what's causing the code? I leaned out the a/f mixture at WOT when I put the long-tubes on, but haven't reprogrammed the computer with the stock tune after putting the exhaust manifolds on. However, I haven't been WOT since the manifolds were re-installed.

 

Its referring to the passenger side rear O2. First thing to check is the wiring to the sensor since you just got done working in that area. Here is the diagnostic info for that code:

DTC P0157 HO2S Circuit Low Voltage Bank 2 Sensor 2
Circuit Description
The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen (O2) 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 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
Criteria 1
• 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 more than 9.0 volts.
• The fuel system is operating in Closed Loop.
• The AIR and the catalyst diagnostics are not active.
• The throttle position (TP) angle is between 2 percent and 70 percent.
OR
Criteria 2
• 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 more than 9.0 volts.
• The AIR and the catalyst diagnostics are not active.
• The Power Enrichment mode is enabled for more than 1.0 second.

Conditions for Setting the DTC
Criteria 1
• The HO2S signal voltage remains below 80 mV.
• The Criteria 1 conditions are present for 80 seconds.
OR
Criteria 2
• The HO2S signal voltage remains below 420 mV.
• The Criteria 2 conditions are present for 10.0 seconds during the Power Enrichment mode.

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.

Conditions for Clearing the MIL/DTC
• The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids
• The PCM sets this DTC when the vehicle runs out of fuel.
• Heated Oxygen Sensor (HO2S) wire--Sensor pigtail may be in contact with the exhaust manifold or the exhaust system.
• An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provides the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Wiring Repairs in Wiring Systems.
• Inspect for an intermittent ground in the signal wire between the connector and the sensor.
• Lean injectors--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool .
• Fuel contamination--Water near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Fuel pressure--System will be lean if fuel pressure is low. Refer to Fuel System Diagnosis .
• Exhaust leaks--An exhaust leak near the HO2S can cause a lean condition. Refer to Inspection Procedure in Engine Exhaust.
• Vacuum or crankcase leaks can cause a lean condition.
• If the above are OK, the HO2S may be at fault.
• For an intermittent condition, refer to Symptoms .

Test Description
The numbers below refer to the step numbers on the diagnostic table.

2. If the HO2S voltage is fixed well below 200 mV, this indicates a short to battery ground or chassis ground. If the voltage is fixed near or above 200 mV, this indicates a short to a PCM ground. When the HO2S voltage is fixed near 200 mV, indicates the DTC set when the fuel system was in a Power Enrichment mode of operation.
Start the engine and idle at the normal operating temperature before performing this test.

3. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature, etc.) that you observed. This isolates when the DTC failed.

4. A sensor that is disconnected should indicate a bias voltage. If the voltage is low inspect the signal circuit for a short to ground.
Lower the exhaust system to gain sufficient access to the HO2S and/or the HO2S connector if necessary.

5. Disconnecting the PCM allows using a DMM in order to test continuity of the circuits. This aids in locating an open or shorted circuit.


Bill

 

You're the man, Bill! I checked the O2 sensor in question today, and the wire wasn't routed away from the exhaust pipe properly. The wire melted where it touched, so I replaced the O2 sensor. Thanks for the informative post. We're lucky to have you on our board.