P0146

DTC P0146 HO2S Insufficient Activity Bank1 Sensor3




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 below200 °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 determines if the HO2S is functioning properly by checking for an adequate number of HO2S voltage transitions above and below the bias range of 300 - 600 mV. This DTC sets when the VCM fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are listed below.
- An open circuit or a short to voltage on either the HO2S signal or HO2S low circuits
- A malfunctioning HO2S
- A problem in the HO2S heater or its circuit
- A poor HO2S ground

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 intrusive tests (i.e., EGR or Catalyst) in progress
- No device control active
- The system voltage is between 11.7 - 18 volts
- The engine run time is greater than 2 minutes
- DFCO mode is not active
- The ECT is 58.5 °C (137 °F) or greater
- The MAF is 13 g/s or greater
- DTC P0147 not active
- The system is in closed loop

Conditions for Setting the DTC
The O2 sensor voltage is between 400 - 473 mV for more than 100 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 connection repairs, refer to Wiring Repairs.

A intermittent may be caused by a poor connection, a rubbed through wire insulation, or a broken wire inside the insulation.

Check for the following conditions:
An exhaust system leak (typically within 30 cm (12 in) up-stream of the HO2S). Refer to Exhaust System Inspection.

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 volt, indicating that the heater works properly. If not, disconnect the HO2S and connect a test lamp between the terminals Cycles if and D. If the test lamp does not light, repair the open in the HO2S ground circuit or the HO2S ignition feed 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 Intermittents and Poor Connections Diagnosis.

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

Step 1:

Steps 2 - 4:

Steps 5 - 7:

Steps 8 - 10:

Steps 11 - 13:

Steps 14 - 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 VCM and the HIGH and LOW circuits between the VCM 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 VCM ground.
13. This step checks for proper circuit resistance between the HO2S LOW circuit and the VCM ground with a cold sensor. A loose HO2S or poor tread 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.