P0152
Diagnostic Chart:
Diagnostic Chart:
Wiring Diagram:
CIRCUIT DESCRIPTION
IMPORTANT: If measured with a megohm digital voltmeter, this may read as low as 0.32 volt.
The Vehicle Control Module (VCM) supplies a voltage of about 0.45 volt (450 mV) between the HO2S signal and the HO2S Low circuits. The Heated Oxygen Sensor (HO2S) varies the voltage from approximately 1.0 volt (1000 mV) during rich conditions to 0.10 volt (100 mV) during lean conditions.
The sensor acts like an open circuit and produces no voltage when the temperature 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 P0152 determines if the HO2S sensor or the circuit is shorted to high by checking for a rich condition during a steady throttle.
CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:
^ No Throttle Position (TP) sensor DTCs.
^ No EVAP DTCs.
^ No Intake Air Temperature (IAT) sensor DTCs.
^ No Manifold Absolute Pressure (MAP) sensor DTCs.
^ No Engine Coolant Temperature (ECT) sensor DTCs.
^ No Mass Air Flow (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 low Manifold Absolute Pressure (MAP) not active.
^ 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 5% but less than 99%.
^ The above met for 5 seconds.
^ Related HO2S DTCs not active since code clear.
Test Enable PE Lean Test
^ A Closed Loop.
^ The Power Enrichment mode active.
^ The high speed fuel cutoff not active.
^ Related HO2S DTCs not active since code clear.
^ Time elapse since test enable is at least 1 second.
Test Enable DFCO Rich Test
^ Decel Fuel cutoff mode is active.
^ A Closed Loop.
^ The time elapsed since the test enable is more than 2 seconds.
^ The HO2S voltage is greater than 468 mV (0.468 V).
ACTION TAKEN WHEN THE DTC SETS
A current DTC P0151 causes the system to operate in open loop. With the DTC P0151 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 drive trips when the test has Run and Passed and not Failed.
^ 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 start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).
^ Use the scan tool Clear Information function.
^ Disconnect the VCM battery feed for 30 seconds.
DIAGNOSTIC AIDS
Check the following items
^ Fuel pressure. System will go rich if pressure is too high. The VCM can compensate for some increase. Refer to Fuel System Diagnosis.
System Diagnosis - Fuel System
^ Rich injector. Perform the Fuel Injector Balance Test for the 4.3L.
Fuel Injector Balance Test
^ Leaking injector. Refer to Fuel System Diagnosis.
System Diagnosis - Fuel System
^ Check for fuel contaminated oil.
^ EVAP canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to EVAP Control System Diagnosis (0).
System Diagnosis - EVAP Control
^ Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
^ TP sensor. An intermittent TP sensor output will cause the system to go rich due to a false indication of the throttle moving.
^ False rich indication due to silicon contamination of the HO2S. This will be indicated by a powdery white deposit on the sensor.
^ Faulty HO2S. If HO2S is internally shorted the HO2S voltage displayed on a scan tool will be over 1 V. Try disconnecting the HO2S; if the displayed voltage goes from over 1000 mV to around 450 mV, replace HO2S. Refer to HO2S Replacement.
^ Never solder the HO2S wires.
TEST DESCRIPTION
The number below refers to the step number on the diagnostic table.
2. This test determines if the conditions exist in order to set the DTC P0152.
3. If the HO2S is internally shorted, the HO2S voltage that is displayed on a scan tool will be over 1.0 volt (1000 mV).