HUMMER DTC P0157

Make:HUMMER
Code:
P0157
Definition:
HO2S Circuit Low Voltage Bank 2 Sensor 2
Description:P0131, P0137, P0151, or P0157

DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0220, P0222, P0223, P0442, P0443, P0446, P0449, P0455, P0496, P1516, P2101, P2119, P2135, P2176 are not set. --->The engine is operating in Closed Loop. The Ignition 1 voltage is between 10-32 V. The fuel level is greater than 10 %. The throttle position (TP) is between 3-70 %. The DTCs run continuously when the above conditions are met for 2 s.Cause:

• P0131, P0137, P0151, or P0157
• The ECM detects that the HO2S voltage is less than 50 mV.
• The DTCs set within 100 s when the above condition is met.

 

MOVED OP's post as it was a near duplicate of another. We do not need to be posting duplicates. Left hummerz code info as helpful should anyone have the issue.

 

PIP4925B

 

PO157 CODE FIXED THIS IS THE THREAD I FOUND AND HAVE RE PASTED, THANKS WHOMEVER POSTED PREVIOUSLY(I COULDN'T FIND)
I WENT DOWN THE LIST AND LO AND BEHOLD THE ENGINE COOLANT TEMPERATURE SENSOR DID IT FOR ME. THANKS FOR THE LAYMAN LAYOUT.

• Check Engine light is the most obvious symptom for Error Code P0157. It will not usually cause drivability issues, since it only suggests an input that measures the efficiency of the catalyst (unlike the front Oxygen sensors). However, there’s a good chance that other error codes may be present as well, such as lean condition codes or pre-O2 sensor codes, which may cause drivability issues, such as the Error Code P0143. For some cases with symptoms, the common symptoms will be:
  • Engine performance problems
  • Rough running
  • Poor idle
  • Engine running rich (happens when the PCM tries to compensate by adding fuel for low oxygen sensor voltage reading)
  • Engine running lean (happens when the vacuum is large enough that PCM will not be able to compensate even by adding fuel)
  • Decrease in fuel economy due to PCM in “limp home” mode
  
  If you suspect your vehicle is running lean, then it is crucial to fix that error and clear the code and check whether the P0157 comes back. Engine running lean could also register lean codes such as P0171 and P0174. Other possible causes of P0157 include:
  • Exhaust air leak in front of O2 sensor which gives false reading
  • Engine running lean
  • Corroded or damaged oxygen sensor
  • Shorted to ground oxygen sensor signal circuit
  • Open ground circuit of oxygen sensor
  • Failed O2 sensor (could be contaminated with coolant or fuel)
  • Damaged PCM (rare)

  How to Check

  Use the OBD-II scanner to collect the freeze frame data of the trouble code. Then, use the scan tool to check the voltage of the O2 sensor to see if it switches properly.
  
  If the trouble code is present, then check it through the live data to see if the engine coolant temperature sensor still works properly. Then, check the pressure of the fuel through the pressure gauge. It should be at 40 psi.
  
  Check the exhaust for any signs of leaks, especially in the pipes and manifold.
  
  Check the rear O2 sensor wires for breaks, shorts and exposed wires.
  
  In some cases, the computer may need to be updated from the dealer. Also, some vehicles may require advanced diagnosis, particularly if there is already a problem in the PCM.
  

  How to Fix

  As with other error codes, repairs for P0157 are done by addressing the issues that arise from the diagnosis, such as:
  
  • Replacement of the rear O2 sensor
  • Repair the cause of the fuel pressure abnormality
  • Repair broken circuits and shorted wires to the O2 sensor
  • Repair faulty engine coolant temperature sensor
  • Replace or update PCM, if necessary
  Error Code P0157 is a moderately serious trouble code. It can definitely cause drivability issues, which can be dangerous when driving at highway speed. Also, if not addressed properly and in a timely manner, it can cause serious damage to catalytic converter, which can be quite expensive to fix.
  
  

 

I think I had this code a while back. I checked the O2 sensors, wiring and everything was good. The Hummer would barely run, it wouldn’t idle at all, the check engine light was flashing instead of just staying on. I thought maybe there was a chance the cats were plugged, pulled them and found good flow so reinstalled them. Did a compression check and found a dead cylinder. I was lucky though I pulled the valve cover off and found one of the springs in three pieces. Went to a machine shop, got a spring off a random lsx head that looked the same, installed it and everything was good again. Just throwing out ideas if someone else runs into the issue.

 

Code P0157 Definition

O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2)

What Does P0157 Mean?

Oxygen sensor 2 is the downstream oxygen sensor in relationship to the catalytic converter. It measures the air-fuel ratio coming out of the catalytic converter to ensure the catalytic converter is functioning properly. The powertrain control module constantly flip-flops between rich and lean air-fuel mixtures due to the input from the upstream oxygen sensor (sensor 1). Whereas, the downstream oxygen sensor (sensor 2) should produce a steady voltage of approximately 0.1-.95 volts if the catalytic converter is doing its job properly and there are no problems with the engine’s air-fuel ratio. When trouble code P0157 is set, this indicates that there is low voltage (roughly 450 millivolts or less) for more than 20 seconds coming from the bank 2 sensor 2 oxygen sensor.

What Are the Symptoms of Code P0157?

• Check Engine Light
• Possible exhaust leaks
• Exhaust odor
• Vehicle running rough
• Lack of power

*No adverse conditions in some cases

What Is the Cause of Code P0157?

• Faulty oxygen sensor (most common)
• Short on voltage to O2 circuit
• Exhaust leaks
• Fuel pressure low
• Engine running lean

How Serious is Code P0157? – Moderate

Driving with trouble code P0157 is acceptable but only for a short period of time. Driving with this code for an elongated period of time could result in greater engine damage if it is being caused by a lean air-fuel ratio.

Code P0157 Common Diagnosis Mistakes

Replacing the O2 sensor without checking for any exhaust leaks or loose connections.

How to Diagnose and Repair Code P0157:

Difficulty of Diagnosis and Repair – 2 out of 5

1. Visually check the O2 sensor wiring and harness connections for any corrosion in the connections or for any physical damage that might be present.
2. Check for exhaust leaks before the sensor and repair as needed.
3. Check sensor voltage after the vehicle has fully warmed up. You should have between .1-.95 volts. If it is less than this, you most likely have a faulty O2 sensor. To be sure, continue diagnosis.
4. Check fuel pressure and compare it to your vehicle specification. (too low of a fuel pressure can cause the engine to run lean causing O2 sensor to read lean aka low voltage.)
5. Conduct a visual and audible inspection of the vacuum lines and any intake connections to make sure there are no signs of disconnection or outside air leaks. (This includes the intake pipe between the throttle body and MAF)

• Listen for a hissing sound, which can be a sign of a vacuum leak.
• Spray water over intake area and listen for idle rpm stumble. If it goes down, then there is an intake leak. Concentrate the stream on different hoses and gaskets until you find your leak.