P0151

Diagnostic Chart:

Diagnostic Chart (cont'd):

Wiring Diagram:

Circuit Description
The VCM supplies a voltage of about 0.45 volt (450 mV) between the HO2S High and HO2S Low circuits. (It measured with a megohm digital voltmeter, this may read as low as 0.32 volt.) The Heated Oxygen Sensor (HO2S Bank 2 Sensor 1) varies the voltage within the range of about 1.0 volt (1000 mV) if the exhaust is rich, down to about 0.10 volt (100 mV) if the exhaust is lean. The DTC P0151 is a type A DTC.

The Sensor is like an open circuit and produces no voltage when it is below 360°C (600°F). The DTC P0151, P0152 or an open sensor circuit or the cold sensor causes the Open Loop operation. The DTC P0151 determines if the HO2S sensor or the circuit is shorted to low by checking for a lean condition during a steady throttle and power enrichment (PE).

Conditions for Setting the DTC
The following conditions will set the DTC:

^ No Throttle Position (TP) sensor DTCs.
^ No EVAP DTCs.
^ No IAT sensor DTCs.
^ No MAP sensor DTCs.
^ No ECT sensor DTCs.
^ No MAF sensor DTCs.
^ No intrusive test in progress.
^ No device controls active.
^ The system voltage measures at least 9.0 volts.

Test Enable Lean Test

^ Closed Loop.
^ No fuel injectors turned off.
^ Air to fuel ratio is at least 14.5 but less than 14.8.
^ The TP is greater than 3.5% but less than 99%.
^ The above met for 5 seconds.
^ The HO2S (Bank 2, Sensor 1) DTCs not active since code clear.
^ HO2S Bank 2 Sensor 1 voltage is less than 0.086 volts (86 mV).

Test Enable PE Lean Test

^ A Closed Loop.
^ The Power Enrichment mode active.
^ The high speed fuel cutoff not active.
^ DTC P0151 not active since code clear.
^ Time elapse since test enable is at least 1 second.
^ The Bank 2 Sensor 1 H02S voltage measures less than 0.598 volts (598 mV).

Action Taken When The DTC Sets
A current DTC causes the system to operate in an Open Loop. With the DTC set, the Malfunction Indicator Lamp (MIL) turns on at the first test failure.

Conditions for Clearing the MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

Test Description
The numbers below refer to the step numbers in the diagnostic table.

2. Running the engine at 1200 RPM keeps the HO2S hot in order to ensure the HO2S remains active and can indicate the exhaust oxygen accurately.
3. Opening the HO2S sensor circuit should result in displayed voltage between 350 and 550 mV. If the display is still fixed below 350 mV, the fault is a short to ground in the HO2S (Bank 2, Sensor 1) high signal circuit or a faulty VCM.