P0137 or P0157 (w/ Denso HO2S)

CIRCUIT DESCRIPTION
This diagnostic applies only to vehicles built with Denso heated oxygen sensors. To identify the heated oxygen sensor refer to Delphi/Denso Sensor in Computers and Control Systems Component Views.

The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between the Heated Oxygen Sensor (HO2S) high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed below a predetermined voltage. If the PCM detects the voltage is below a predetermined voltage, a Diagnostic Trouble Code (DTC) sets.

CONDITIONS FOR RUNNING THE DTC
^ DTC P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1415, P1416, P1514, P1515, P1516, P1517, or P1518 are not set.
^ The air fuel ratio is between 14.5:1 and 14.7:1.
^ Vehicles without Throttle-actuated Control (TAC), the Throttle Position (TP) is between 3-70 percent.
^ Vehicles with Throttle-actuated Control (TAC) the Throttle Position (TP) indicated angle is between 3-70 percent more than the value observed at idle.
^ The loop status is closed.
^ The ignition 1 signal is between 9-18 volts.
^ The fuel tank level remaining is more than 10 percent.
^ Intrusive test are not in progress.
^ The scan tool output controls are not active.

CONDITIONS FOR SETTING THE DTC
The HO2S voltage is less than 80 mV for 400 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS

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

Check for the following conditions:
^ A sensor pigtail may be mispositioned and contacting the exhaust system.
^ An intermittent short to ground in the signal circuit between the PCM connector and HO2S
^ A poor PCM to the engine block ground
^ Lean injectors-Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2. Component Tests and General Diagnostics
^ 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. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool). Component Tests and General Diagnostics
^ 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. Component Tests and General Diagnostics
^ Exhaust leaks-If there is an exhaust leak, the engine may pull the outside air into the exhaust and past the sensor. Refer to Exhaust Leakage in Exhaust System. Testing and Inspection
^ Vacuum or Crankcase leaks can cause a lean condition or possibly a high idle.

TEST DESCRIPTION

Steps 1-5:

Steps 6-11:

The number below refer to the step number on the diagnostic table.
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 lean conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S needs replacement or a lean condition exists only on the suspect HO2S cylinder bank.