DTC P0137 HO2S Circuit Low Voltage Sensor 2. Chevrolet Blazer

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Blazer - 2WD 🢒 DTC 🢒 DTC P0137 HO2S Circuit Low Voltage Sensor 2

Handling ESD Sensitive Parts Notice
Engine Controls Components
Pre and Post Oxygen Sensors
OBD II Symbol Description Notice

Circuit Description

The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal relative to the oxygen storage capacity of the catalytic converter. The PCM can then determine the ability of the catalytic converter to convert the exhaust emissions effectively. The HO2S 2 signal will be far less active than the signal produced by the front Oxygen Sensor 1 (O2S 1).

Conditions for Setting the DTC

•	The Throttle Position (TP) sensor is between 5 % and 50 % (auto).

•	The Throttle Position (TP) sensor is between 10 % and 50 % (manual).

•	The Air Fuel (A/F) Ratio is between 14.5:1 and 14.7:1.

•	The engine coolant temperature is greater than 40° C (158° F).

•	The vehicle is in a Closed Loop.

•	The above conditions are met for 50 seconds

•	The HO2S 2 remains below 22 mV for 112 seconds (auto).

•	The HO2S 2 remains below 22 mV for 100 seconds (manual).

•	One or more of the following DTCs are not set, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300-P0304, P0506, P0507, P1406, P1441.

Action Taken When the DTC Sets

•	The Malfunction Indicator Lamp (MIL) illuminates after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information.

•	A history DTC is stored.

Conditions for Clearing the MIL/DTC

•	The malfunction indicator lamp (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.

•	A history DTC will clear after 40 consecutive warm up cycles without a fault.

•	Use a scan tool to clear the DTCs.

Diagnostic Aids

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

A rubbed through wire insulation or a wire contacting the exhaust may cause an intermittent.

Check for the following conditions:

•	The exhaust system - Inspect the exhaust system for leaks. Check exhaust between the three way catalytic converter and the flange for leaks, corrosion, or for loose or missing hardware and repair as necessary.

•	A poor connection or damaged harness - Inspect the harness for a short to ground in rear HO2S 2 high circuit, improper mating, or broken locks. Ensure that the HO2S 2 pigtail is not contacting the exhaust.

•	An intermittent test - Observe the rear HO2S 2 on the scan tool while moving related connectors and wiring harness with the key ON. Whenever the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction.

Test Description

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

The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.

This step determines if DTC P0137 is the result of a hard fault or an intermittent condition.

Jumpering the rear HO2S 2 low circuit to ground is necessary to allow the PCM to display the supplied bias voltage. Whenever the voltage is between 0.35 and 0.55 volt, then the wiring and PCM are OK.

Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Reprogram the replacement PCM. Refer to the latest Techline information for programming procedures.

Step	Action	Value(s)	Yes	No
1	Was the Powertrain On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Turn the ignition ON leaving the engine OFF. Install the scan tool. Is the HO2S 2 voltage less than the specified value?	200 mV (0.20 V)	Go to Step 4	Go to Step 3
3	Turn the ignition ON leaving the engine OFF. Review the Freeze Frame data. Make a note of the parameters. Operate the vehicle within the Freeze Frame conditions and conditions for setting the DTC as noted. Is the HO2S 2 voltage less than the specified value?	47 mV (0.47 V)	Go to Step 4	Go to Step 8
4	Disconnect the HO2S 2 electrical connector and jumper the HO2S 2 low circuit (PCM side) to a ground. Does the scan tool indicate HO2S 2 voltage within the specified value?	350 mV-550 mV (0.35 V-0.55 V)	Go to Step 7	Go to Step 5
5	Turn the ignition OFF. Disconnect the PCM connectors and check the HO2S 2 high circuit for a short to ground or a short to the sensor ground circuit. If a problem is found repair as necessary. Refer to Wiring Repairs in Engine Electrical. Was a problem found?	--	Go to Step 8	Go to Step 6
6	Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete?	--	Go to Step 8	--
7	Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Is the action complete?		Go to Step 8	--
8	Using the scan tool, clear the DTCs. Start the Engine. Allow the engine to idle until the engine reaches the specified temperature. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text. Does the scan tool indicate that this diagnostic ran and passed?	90°-95° C	Go to Step 9	Go to Step 2
9	Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed?	--	Go to the Applicable DTC Table	System OK