P0140
DTC P0140 HO2S Circuit Insufficient Activity Sensor 2
Circuit Description
The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal proportional to the oxygen storage capacity of the catalytic converter. The PCM uses this signal to measure the ability of the catalytic converter to convert the exhaust emissions effectively. The HO2S 2 signal is much less active than the signal produced by the front oxygen sensor 1 (O2S 1).
Conditions for Running the DTC
- There are no active manifold absolute pressure (MAP) DTCs
- There are no active intake air temperature (IAT) DTCs
- There are no active engine coolant temperature (ECT) DTCs
- There are no active throttle position (TP) DTCs
- There are no active fuel trim DTCs
- There are no active injector control DTCs
- There are no active misfire DTCs
- There are no active crankshaft position (CKP) DTCs
- There are no active evaporative emissions (EVAP) DTCs
- There are no active idle air control (IAC) DTCs
- The air flow is more than 5.5 grams per second.
- Engine Coolant Temperature (ECT) is more than 40° C (104° F).
- Throttle Position (TP) is between 4% and 56%.
- The above conditions are met for 140 seconds.
Conditions for Setting the DTC
The HO2S 2 signal remains between 425 - 460 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 ignition cycles.
- The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is recorded in the scan tool's Freeze Frame and Failure Records.
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.
- The DTCs can be cleared using the scan tool Clear Information function.
Diagnostic Aids
Whenever the oxygen sensor pigtail wiring, the connector, or the 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 rear HO2S 2 must have a clean air reference. This clean air reference is obtained through 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 performance of the oxygen sensor.
A poor connection, rubbed through wire insulation, or a wire broken inside of the insulation may cause an intermittent fault to occur.
Check for the following conditions:
A poor connection or damaged harness -Inspect the PCM harness for the following condition:
- An open in the rear HO2S high circuit
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connections
- A damaged harness
An intermittent test: With the key ON, observe the rear HO2S 2 on the scan tool while moving the related connectors and wiring harnesses. If the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction.
Steps 1 - 3:
Steps 4 - 6:
Steps 7 - 9:
Step 10:
Steps 11 - 12:
Steps 13 - 16:
Steps 17 - 18:
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. 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.
4. This step checks the PCM and the HIGH and LOW circuits between the PCM and the HO2S connector for proper operation.
7. This step checks for proper HO2S heater circuit operation up to the HO2S connector.
8. This step checks for proper circuit resistance between the HO2S LOW circuit and PCM ground.
13. 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 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.