W/Isolated Grounded HO2S
CIRCUIT DESCRIPTIONThis diagnostic applies only to vehicles built with isolated grounded heated oxygen sensors (HO2S). In order to identify the HO2S, refer to Computers and Controls Systems Component views.
The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The HO2S varies the voltage over a range of about 1,000 mV when the exhaust is rich to 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
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.
^ The vehicle is operating in Closed Loop.
^ The ignition 1 signal is between 9-18 volts.
^ The fuel tank level remaining is more than 10 percent.
^ The fuel alcohol content is less than 90 percent.
^ Intrusive tests are not in progress.
^ The scan tool output controls are not active.
Lean Test Enable:
^ The air fuel ratio is between 14.5:1-14.7:1.
^ For vehicles with throttle-actuated control (TAC), the throttle position (TP) indicated angle is between 3-70 percent more than the value observed at idle.
^ For vehicles without TAC, the TP is between 3-70 percent.
Power Enrichment Test Enable:
^ Power enrichment is active.
^ The above condition is met for 1 second.
CONDITIONS FOR SETTING THE DTC
Lean Test:
The HO2S voltage is less than 200 mV for 165 seconds.
Power Enrichment Test:
The HO2S voltage is less than 360 mV for 10 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.
^ The control module commands Open Loop.
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.
^ Clear the MIL and the DTC with a scan tool.
DIAGNOSTIC AIDS
IMPORTANT: Never solder the HO2S wires. For proper wire and connection repair, refer to Wiring Repairs in Diagnostic Aids.
Using the scan tool, observe the long term fuel trim values at the different RPM and the air flow conditions. The scan tool also displays the fuel trim cells, so the long term 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 long term fuel trim values measure around 158 or more.
Inspect 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
^ Any lean injectors. Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2. Testing and Inspection
^ Any 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 (W/O Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (W/ Special Tool). Testing and Inspection
^ The fuel pressure. If the pressure is too low, the system will be lean. In order to confirm the fuel pressure, monitor the fuel pressure while driving the vehicle at various speeds and loads. Refer to Fuel System Diagnosis, Component Tests and General Diagnostics
^ Any 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.
^ Any vacuum or crankcase leaks can cause a lean condition or a high idle.
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 Testing for Intermittent and Poor Connections in Diagnostic Aids.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Diagnostic Aids.
TEST DESCRIPTION
Steps 1-3:
Steps 4-11:
The numbers below refer to the step numbers 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.