Snap a picture. It should be behind the large catalytic converter and may be just out of sight.

 

DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1



<A href="#ss1-554109">Circuit Description

The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.
Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.
This diagnostic trouble code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the vehicle control module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:
This DTC is designed to detect an HO2S voltage that remains at a low (lean) voltage for more than a specified number of seconds during the test conditions. This DTC is set under the following conditions:
<A href="#ss2-554109">Conditions for Running the DTC


here is a electrical layout picture.

The number below refer to the step number on the diagnostic table.

1. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for lean conditions that may affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S needs replacement or a lean condition exists only on the suspect HO2S cylinder bank.

Step
Action
Values
Yes
No
1
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
--
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check
2

1. Run the engine until normal operating temperature is reached.
2. Use the scan tool in order to monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage fixed less than the value specified?
86 mv
Go to Step 4
Go to Step 3
3
This DTC is intermittent.
Are any additional DTCs stored?
--
Go to applicable DTC
Go to Diagnostic Aids
4

1. Turn OFF the ignition.
2. Disconnect the HO2S connector for the sensor that applies to this DTC.
3. Jumper the HO2S LOW circuit terminal (Engine harness side) to a known good ground.
4. Turn ON the ignition, with the engine OFF.
5. Use the scan tool in order to monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage within the specified value range?
351-551 mV
Go to Step 5
Go to Step 6
5

1. The HO2S may be detecting a lean exhaust condition. Check for one of the following conditions:
   • HO2S connector water intrusion
   • An exhaust leak between the HO2S and the engine
   • Vacuum leaks
   • Incorrect fuel pressure
   • Lean fuel injectors
   • An inaccurate MAF sensor
2. Repair any of the above or similar engine conditions as necessary.

Did you find a problem?
--
Go to Step 10
Go to Step 8
6

1. Turn OFF the ignition.
2. Remove the jumper from the HO2S LOW circuit terminal.
3. Disconnect the VCM connector that contains the HO2S HIGH signal circuit.
4. Use a DMM in order to measure and record the resistance between the HO2S HIGH signal circuit and ground.
5. Measure and record the resistance between the HO2S HIGH signal circuit and the HO2S LOW circuit.

Is the resistance at the specified value on both tests?
--
Go to Step 9
Go to Step 7
7
Repair the HO2S signal HIGH circuit shorted to ground or shorted to the HO2S LOW circuit. Refer to Wiring Repairs in Wiring Systems.
Is the action complete?
--
Go to Step 10
--
8
Replace the HO2S. Refer to Heated Oxygen Sensor Replacement .
Is the action complete?
--
Go to Step 10
--
9
Important: The replacement VCM must be programmed.
Replace the VCM. Refer to VCM Replacement/Programming .
Is the action complete?
--
Go to Step 10
--
10

1. Use the scan tool in order to Clear the DTCs.
2. Start the engine.
3. Allow the engine to idle until the engine reaches normal operating temperature.
4. Select the DTC and the Specific DTC function.
5. Enter the DTC number which was set.
6. Operate the vehicle within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate that this diagnostic Ran and Passed?
--
Go to Step 11
Go to Step 2
11
Does the scan tool display any additional undiagnosed DTCs?
--
Go to applicable DTC
System OK

all this information is from the GM data base for service and repair i have access to this from the dealer i work at so i dont have a problem giving you the information. enjoy. pm if you need any more charts.

 

You must have missed my first reply to this thread where I posted the identical information.

 

I have since replaced both o2 sensors with n ot luck. I then removed the o2 sensor in front of the cat still the same. Tonight i put a fuel pressure guage on itAt about 55-56pis it would start then drop to about 50 if reved a little it would dropdown as low as 40 and stall out. Tried to start again was at about 55 psi started dropped and stalled. What should the psi be while running and also being brought up to a high idle say 2500. thanks

 

we had a s-10 that did exactly that. Turned out to be the fuel pump

 

i got p0151 and replaced the o2 sensor and the code came back any ideas?

 

Diagnosing the issue would be a good place to start. Just throwing parts at a problem can get expensive.

 

I agree just not sure where to start, i just had the spider replaced and plugs and all that stuff, just not sure where else to look

 

The links at the top of this thread provide the diagnostic procedure from start to end that will get to the root cause of the problem.

 

thanks will work on it