P0137
Diagnostic Chart:
Wiring Diagram:
CIRCUIT DESCRIPTION
The VCM supplies a voltage of approximately 0.45 volt (450 mV) between the HO2S High and HO2S Low circuits.
IMPORTANT: It the voltage is measured with a 10 megaohm digital voltmeter, the voltage may reach as low as 0.32 volt. 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.
When the HO2S temperature measures below 360°C (600°F) the sensor will not produce any voltage. The sensor will behave like an open circuit. This will result in an open loop operation.
The HO2S heater provides for a taster sensor warm-up which allows the sensor to become active in a shorter period of time. The sensor will also remain active during a long extended idle.
The DTC P0137 determines if the HO2S or circuit is shorted 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 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 Low MAP not active
^ Closed Loop
^ 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
^ HO2S voltage is less than 0.086 volt (86 mV)
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
^ HO2S voltage is less than 0.598 volt (598 mV)
ACTION TAKEN WHEN THE DTC SETS
The VCM turns on the MIL (Malfunction Indicator Lamp) after 2 consecutive failures.
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 startup 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
IMPORTANT: Never solder the HO2S wires. For proper wire and connector repair refer to Wiring Repairs in Electrical Diagnosis.
Using the scan tool, observe the LT fuel trim values at the different RPM and the air flow conditions. The scan tool also displays the fuel trim cells, so the LT fuel trim values can be checked in each of the cells in order to determine when the DTC may have set. If the conditions for this DTC exist, the LT fuel trim values measure around 158 or greater.
Check for the following conditions:
^ A sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ An intermittent ground in wire between the connector and the sensor.
^ A poor VCM ground.
^ Lean injectors: Perform the Injector Balance Test. Refer to Fuel Injector Balance Test. Fuel Injector Balance Test
^ Fuel Contamination: Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can also set this DTC.
^ Fuel pressure: If the pressure is too low, the system will be lean. In order to confirm, monitor a fuel pressure while driving the vehicle at various speeds and loads. Refer to Fuel System Diagnosis. System Diagnosis - Fuel System
^ Exhaust leaks: If there is an exhaust leak, the engine may pull the outside air into the exhaust. and past the sensor.
^ Vacuum or the Crankcase leaks can cause a lean condition or a possibly a high idle.
TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Running the engine at 1200 RPM keeps the HO2S temperature hot in order to ensure the HO2S remains active. Running the engine at 1200 RPM can indicate the exhaust oxygen content accurately.
3. Opening the HO2S circuit should result in a displayed voltage between 350 and 550 mV. If the display is still fixed below the 350 mV, the fault is a short to a ground in the HO2S high signal circuit or a faulty VCM.