DTC P0140 HO2S Circuit Insufficient Activity Sensor 2. Isuzu S/T Isuzu

For 1990-2009 cars only

Makes 🢒 Isuzu 🢒 2000 🢒 S/T Isuzu - 2WD 🢒 DTC 🢒 DTC P0140 HO2S Circuit Insufficient Activity Sensor 2

Circuit Description

The heated oxygen sensor 2 (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 powertrain control module (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, P0169, P0171, P0172, P0178, P0201, P0202, P0203, P0204, P0300, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602 or P1441 are not set.

•	Air flow is more than 5.5 grams per second.

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

•	The above conditions are met for 70 seconds.

•	Engine run time is more than 30 seconds in Closed Loop.

•	The throttle position (TP) is between 8 percent and 56 percent.

Conditions For Setting The DTC

HO2S 2 remains between 425 mV and 460 mV for 125 seconds.

Action Taken When the DTC Sets

•	The malfunction indicator lamp (MIL) will illuminate after 2 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 is stored.

Conditions for Clearing the MIL/DTC

•	The 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.

•	A scan tool can clear the DTCs.

Diagnostic Aids

Important: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Inspect for exhaust system leaks upstream of the suspect HO2S. The leak may be very small and typically be within 30.5 cm (12 inches) of the suspect HO2S. Refer to Exhaust Leakage in Engine Exhaust.

A Malfunctioning HO2S Heater or Heater Circuit

With the ignition ON and the engine OFF, the HO2S voltage displayed on a scan tool should gradually drop to below 0.150 volts, indicating that the heater works properly. If not, disconnect the HO2S and connect a test lamp between the terminals C and D. If the test lamp does not light, repair the open in the HO2S ground circuit or the HO2S ignition positive voltage circuit. If the test lamp lights, replace the HO2S.

The Intermittent Test

Use a scan tool in order to monitor this HO2S signal voltage. Move the related connectors and the wiring harness with a warm engine running at part throttle in Closed Loop. If the failure is induced, the HO2S signal voltage reading changes from its normal fluctuating voltage (above 600 mV and below 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction.

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 Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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

Test Description

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

This step checks for proper sensor activity. When in Closed Loop fuel control, the HO2S voltage should rapidly swing above and below the bias voltage.

This step checks the PCM and the HIGH and LOW circuits between the PCM and the HO2S connector for proper operation.

This step checks for proper HO2S heater circuit operation up to the HO2S connector.

This step checks for proper circuit resistance between the HO2S LOW circuit and PCM ground.

This step checks for proper circuit resistance between the HO2S LOW circuit and PCM ground with a COLD sensor. A loose HO2S or poor thread to the exhaust electrical contact will cause higher resistance when the HO2S is cold. Although 500 ohms is allowed, typical resistance should be less than 50 ohms.

Step

Action

Values

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

Use a scan tool in order to store the DTC information from the PCM into the scan tool.
Clear the DTC information from the PCM.
Reset the fuel trim values.
Start and idle the engine until the normal operating temperature is reached.
Use a scan tool in order to monitor the HO2S voltage.

Is the HO2S voltage fixed within the voltage range specified?

400-473 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.
Disconnect the HO2S connector for the sensor that applies to this DTC.
Jumper the HO2S return circuit to a clean body ground.
Jumper the HO2S signal circuit to a clean body ground.
Turn ON the ignition, with the engine OFF.
Use a scan tool in order to monitor the HO2S voltage.

Is the voltage less than the specified value?

20 mV

Go to Step 7

Go to Step 5

Turn OFF the ignition.
Remove the jumpers from the HO2S terminals.
Disconnect the PCM connector containing the HO2S signal and return circuits.
Using a DMM, measure the continuity of the HO2S signal circuit and then the HO2S return circuit between the PCM connector terminal and the HO2S connector terminal on the engine harness side.

Is the resistance of both circuits less than the specified value?

5 ohms

Go to Step 6

Go to Step 9

Check for proper PCM connector terminal contact.
Repair the connectors as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find a condition?

Go to Step 17

Go to Step 16

Remove the jumpers from the HO2S terminals.
Connect a test lamp between the HO2S heater ignition positive voltage and heater ground circuit terminals on the engine harness side.
Ensure the ignition is ON while the engine is OFF.

Is the test lamp ON?

Go to Step 8

Go to Step 10

Turn OFF the ignition.
Reconnect the HO2S connector.
Disconnect the PCM connector containing the HO2S return circuit and the PCM connector containing the PCM ground circuits.
Using a DMM, measure the resistance between the HO2S return circuit terminal and one of the PCM ground circuit terminals.

Is the resistance less than the specified value?

5 ohms

Go to Step 12

Go to Step 11

Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 17

Repair the HO2S heater ignition positive voltage circuit or ground circuit. Refer to Wiring Repairs in Wiring Systems.

Probable causes include the following:

•	An open circuit

•	High circuit resistance

•	Poor ground connections

•	A blown heater fuse--other DTCs should set.

Is the action complete?

Go to Step 17

Repair the high resistance between the HO2S return circuit and the PCM ground circuit. Refer to Wiring Repairs in Wiring Systems. Probable causes include the following:

•	A poor HO2S connector terminal contact.

•	An open sensor harness return circuit--this requires HO2S replacement.

•	A sensor harness return circuit with high resistance--this requires HO2S replacement.

•	A poor PCM ground connection.

•	High PCM ground circuit resistance.

•	An ungrounded exhaust system.

Is the action complete?

Go to Step 17

Check for exhaust system leaks upstream of the suspect HO2S. The leak may be very small and typically will be within 12 inches of the suspect HO2S.
Repair the exhaust system as necessary. Refer to Exhaust System Inspection in Engine Exhaust.

Did you find a condition?

Go to Step 17

Go to Step 13

Allow engine to cool to ambient temperature.
Remeasure the resistance between the HO2S return circuit terminal and a PCM ground circuit terminal.

Is the resistance less than the specified value?

5 ohms

Go to Step 15

Go to Step 14

Remove the HO2S from the exhaust.
Clean the HO2S mounting threads.
Apply anti-seize compound P/N 5613695 or equivalent to the sensor threads.
Tighten the HO2S to the proper torque.
Remeasure the resistance between the HO2S return circuit terminal and a PCM ground circuit terminal.

Is the resistance less than the specified value?

5 ohms

Go to Step 17

Go to Step 15

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

Is the action complete?

Go to Step 17

Important: The replacement PCM must be programmed.

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

Go to Step 17

Use the scan tool in order to clear the DTCs.
Start the engine.
Allow the engine to idle until the engine reaches the normal operating temperature.
Select DTC and the Specific DTC function.
Enter the DTC number which was set.
Operate the vehicle within 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 18

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go to applicable DTC table

System OK