DTC P0137 HO2S Circuit Low Voltage Sensor 2. Isuzu S/T Isuzu

For 1990-2009 cars only

Makes 🢒 Isuzu 🢒 1999 🢒 S/T Isuzu - 4WD 🢒 DTC 🢒 DTC P0137 HO2S Circuit Low Voltage Sensor 2

Engine Controls Components
Cell 20: EGR Valve, EVAP and IAC Controls
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts 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 Running the DTC

•	DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0200, P0300, P0301, P0302, P0303, P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set.

•	The air flow is more than 5.5 grams per second.

•	The engine coolant temperature (ECT) is more than 40°C (104°F).

•	The throttle position (TP) angle is between 5 percent and 50 percent for 4 seconds.

Conditions For Setting The DTC

HO2S 2 remains below 22 mV for 150 seconds.

Action Taken When the DTC Sets

•	The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present.

•	The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

•	A history DTC stores.

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 number(s) below refer(s) to the step number(s) 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 information for later reference.

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

It is necessary to jump the HO2S 2 low circuit to ground in order to allow the PCM to display the supplied bias voltage. The PCM and the wiring are OK if the voltage is between 0.35 and 0.55 volt .

Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communications System (ITCS) information for PCM programming and Crankshaft Position System Variation Learn for the crankshaft position system variation learn procedure.

DTC P0137-Heated Oxygen Sensor (HO2S) Circuit Low Voltage (Sensor 2)

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

Turn ON the ignition switch leaving the engine OFF.
Install a 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

Review the Freeze Frame data and record the parameters.
Start the engine.
Operate the vehicle within the Freeze Frame conditions and Conditions For Setting the DTC as specified

Is the HO2S 2 voltage less than the specified value?

40 mV (0.04 V)

Go to Step 4

Go to Step 8

Turn OFF the ignition switch.

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

Disconnect the HO2S 2 electrical connector.
Connect a jumper wire to the HO2S 2 sensor low circuit (PCM side) to ground.
Turn ON the ignition switch leaving the engine OFF.

Does the scan tool indicate the 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

Turn OFF the ignition switch.
Disconnect the PCM electrical connectors.
Check the HO2S 2 sensor signal circuit for the following condition(s):

•	Short to ground

•	Short to the HO2S 2 sensor ground circuit

Repair the electrical connectors and the circuits as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 8

Go to Step 6

Replace the PCM. Refer to the Powertrain Control Module Replacement .

Is the action complete?

Go to Step 8

Turn OFF the ignition switch.

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

Replace the HO2S 2 sensor. Refer to the Heated Oxygen Sensor Replacement .

Is the action complete?

Go to Step 8

Clear the DTCs with the scan tool.
Start the engine.
Idle the engine at the normal operating 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 has ran and passed?

Go to Step 9

Go to Step 2

Check to see if any additional DTCs are set.

Does the scan tool display any DTCs that you have not diagnosed?

Go to applicable DTC table

System OK