DTC P0131 O2S Circuit Low Voltage Sensor 1. GMC Truck Sonoma Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 Sonoma Pickup - 2WD 🢒 DTC 🢒 DTC P0131 O2S Circuit Low Voltage Sensor 1

Engine Controls Components
Cell 20: Oxygen Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

Circuit Description

The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volts to the Oxygen Sensor 1 (O2S 1). The O2S 1 varies the voltage between a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if the exhaust is lean.

The O2S 1 is like an open circuit and produces no voltage when the O2S 1 temperature is below 315°C (600°F). An open O2S 1 circuit or cold sensor causes an Open Loop operation.

Conditions For Running The DTC

•	No active MAP DTC's

•	No active IAT DTC's

•	No active ECT DTC's

•	No active TP DTC's

•	No active Fuel Trim DTC's

•	No active Injector Control DTC's

•	No active Misfire DTC's

•	No active CKP DTC's

•	No active EVAP DTC's

•	No active IAC DTC's

•	No active PCM Memory DTC's

•	Air flow is more than 3 grams per second.

•	Engine Coolant Temperature (ECT) is more than 70°C (158°F).

•	Engine is operating in Closed Loop.

•	Throttle Position (TP) angle is between 5 percent and 50 percent.

•	Engine has been in the above conditions for 20 seconds.

Conditions For Setting The DTC

O2S 1 voltage is less than 52 mV for 125 seconds.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.

•	The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.

Conditions for Clearing the MIL or DTC

•	The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.

•

A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.

•	Use a scan tool in order to clear the DTCs.

Diagnostic Aids

•	The Fuel Pressure - System will run lean if the fuel pressure is too low. Monitor the fuel pressure while driving the vehicle at various road speeds and loads in order to confirm. Refer to Fuel System Diagnosis .

•

The Map Sensor - An output that causes the PCM to sense a lower than normal manifold pressure, or high vacuum, can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed, or defaulted, value for the MAP sensor. When the lean condition is gone when the sensor is disconnected, substitute a known good sensor and recheck.

•	A fuel contamination - Water, in even small amounts, near the fuel pump inlet can be delivered to the fuel injector. The water causes a lean exhaust and a DTC P0131 can set.

•	The O2S harness - the O2S 1 pigtail may be mis-positioned and contacting the exhaust manifold.

•	An engine misfire A misfire will result in unburned oxygen in the exhaust, which can cause DTC P0131. Refer to Symptoms .

•	A cracked Oxygen sensor (O2S) - A cracked O2S or poor ground at the sensor can cause a DTC P0131. Refer to Symptoms .

•	A plugged fuel filter - A plugged fuel filter can cause a lean condition and cause a DTC P0131 to set.

•	A plugged Oxygen Sensor (O2S) - A plugged reference port on the Oxygen Sensor (O2S) will indicate a lower then normal voltage output from the O2S.

Whenever the oxygen sensor pigtail wiring, connector or terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, connector or terminals. In order for the sensor to function properly, the O2S must have a clean air reference provided. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the O2S sensor wires, connectors or terminals could result in the obstruction of the air reference degrading the performance of the oxygen sensor.

An intermittent may be caused by any of the following conditions:

•	A poor connection

•	Rubbed through wire insulation

•	A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

This step determines if the DTC P0131 is the result of a hard malfunction or an intermittent condition. It may be necessary to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.

Program the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming.

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Run the engine until normal operating temperature is reached.
Using the scan tool monitor the O2S voltage for the sensor that applies to this DTC.

Is the O2S voltage fixed less than the value specified?

44 mV

Go to Step 4

Go to Step 3

This DTC is intermittent.

Are any additional DTCs stored?

Go to applicable DTC table

Go to Diagnostic Aids

Turn OFF the ignition.

Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.

Disconnect the O2S harness connector.
Turn ON the ignition leaving the engine OFF.

Does the scan tool indicate that the O2S voltage is within the specified values?

351 - 551 mV

Go to Step 5

Go to Step 6

The O2S may be detecting a lean exhaust condition. Check for one of the following condition:

•	O2S connector water intrusion

•	An exhaust leak between the O2S and the engine. Refer to Exhaust System Inspection in Engine Exhaust.

•	Vacuum leaks

•	Incorrect fuel pressure. Refer to Fuel System Diagnosis .

•	Lean fuel injectors. Refer to Fuel Injector Balance Test

•	An inaccurate MAF sensor

Repair any of the above or similar engine conditions as necessary.

Did you find a problem?

Go to Step 10

Go to Step 8

Turn OFF the ignition.
Disconnect the PCM connector that contains the O2S HIGH signal circuit.
Using a J 39200 DMM measure and record the resistance between the O2S HIGH signal circuit and ground.

Is the resistance at the specified value?

∞

Go to Step 9

Go to Step 7

Repair the O2S signal HIGH circuit shorted to ground . Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 10

Replace the O2S. Refer to Oxygen Sensor Replacement .

Is the action complete?

Go to Step 10

Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

Go to Step 10

Using the scan tool, clear the DTCs.
Start the engine.
Allow the engine to idle until the engine reaches normal operating temperature.
Select DTC and the Specific DTC function.
Enter the DTC number which was set.
Operate the vehicle , with the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

Go to Step 11

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go to the applicable DTC table

System OK