P0152

DTC P0152 HO2S Circuit High Voltage Bank2 Sensor1




Circuit Description

IMPORTANT: If the voltage is measured with a 10 Megohm DMM, the voltage may read as low as 0.32 volt.

The HO2S does not produce a voltage at temperatures below 200 °C (392 °F). When the HO2S is below 200 °C (392 °F), the VCM will default to a 450 mV reference voltage. When the HO2S temperature is below 200 °C (392 °F), the oxygen sensor voltage displayed on the scan tool will be near the 450 mV reference signal. The VCM holds the fuel control system in open loop operation until the sensor reaches operating temperature. The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time. When the HO2S temperature exceeds 200 °C (392 °F), the sensor begins producing a voltage that varies in response to exhaust oxygen levels. This voltage ranges from a high of approximately 900 mV under rich exhaust conditions, to a low of approximately 100 mV under lean exhaust conditions. These voltage transitions from rich-to-lean and lean-to-rich occur rapidly when the VCM is in control of the air/fuel ratio (closed loop operation).

This DTC is designed to detect an HO2S voltage that remains at a high (rich) voltage for more than a specified number of seconds during the test conditions. This DTC is set under the following conditions:
- There is an HO2S circuit fault that results in a false rich exhaust condition.
- The HO2S is correctly detecting the rich air/fuel ratio resulting from either a fuel control or emission system problem.

Conditions for Running the DTC
- No active TP sensor DTCs
- No active EVAP system DTCs
- No active IAT sensor DTCs
- No active MAP sensor DTCs
- No active ECT sensor DTCs
- No active MAF sensor DTCs
- No active misfire DTCs
- No intrusive test in progress
- No device controls active
- The system voltage is between 11.7 - 18 volts

Rich Test Enable
- The system is in closed loop
- The air/fuel ratio is between 14.5 - 14.8
- The throttle position is between 0 - 50%
- The above conditions are met for 5 seconds

Decel Fuel Cut-Off (DFCO) Rich Test Enable
- The system is in closed loop.
- DFCO mode active
- The elapsed time since test enabled is greater than 2 seconds.

Conditions for Setting the DTC

Rich Test
The O2 sensor voltage is greater than 976 mV for more than 40 seconds.

Decel Fuel Cut-Off Rich Test
The O2 sensor voltage is greater than 468 mV for more than 30 seconds.

Action Taken When the DTC Sets
- The VCM illuminates the MIL (Malfunction Indicator Lamp) if a failure is detected during 2 consecutive key cycles.
- The VCM will set the DTC and records the operating conditions at the time the diagnostic fails. The VCM stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC
- The VCM 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 (coolant temperature has risen 22 °C (40 °F) from the startup coolant temperature and the engine coolant temperature is more than 70 °C (158 °F) during the same ignition cycle).
- Use the scan tool Clear Information function.

Diagnostic Aids

IMPORTANT: Never solder the HO2S wires. For proper wire and connector repair, refer to Wiring Repairs or Connector Repairs.

Check the following items:
- The fuel pressure: If the pressure is too high, the system will run rich. The VCM can compensate for some increase; however, if the pressure gets too high, this DTC may set. Refer to Fuel System Diagnosis.
- A rich injector. Perform an Injector Balance test.
- A leaking injector. Refer to Fuel System Diagnosis.
- Fuel contaminated oil
- EVAP canister purge: Check for a fuel saturation. If full of fuel, check the canister control and hoses. Refer to Fuel System Cleaning.
- Leaking fuel pressure regulator diaphragm by checking the vacuum line to the regulator for fuel.
- The TP sensor: An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving.
- False rich indication due to silicon contamination of the heated oxygen sensor. This DTC, accompanied by a lean driveability condition and a powdery white deposit on the sensor, may indicate a false rich condition.

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.

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

Steps 1 - 4:

Steps 5 - 7:

Steps 8 - 11:

Test Description
The number below refers to the step number on the diagnostic table.
3. In order to determine if the engine is rich during De- acceleration Fuel Cut-Off (DFCO) operate the vehicle up to highway speed conditions and release the accelerator pedal allowing the vehicle to coast in gear. Monitor the scan tool HO2S voltage and the DFCO parameter. A rich condition will cause HO2S voltage to be above 468 mV during DFCO.

An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.

5. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.
8. An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.