System Description
Oxygen sensors (O2S) are used for fuel control and post catalyst monitoring. Each O2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The O2S must reach operating temperature to provide an accurate voltage signal. A heating element in O2S 2 minimizes the time required for the sensor to reach operating temperature. The powertrain control module (PCM) supplies the O2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the O2S voltage signal. Once the O2S reaches operating temperature and Closed Loop is achieved, the O2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High O2S voltage indicates a rich exhaust stream. Low O2S voltage indicates a lean exhaust stream. If the PCM detects that O2S 1 voltage stays below a specified value, DTC P1171 will set.
Conditions for Running the DTC
| • | DTCs P0122, P0123, P0131, P0132, P0133, P0134 are not set. |
| • | The ECT Sensor parameter is more than 20°C (68°F). |
| • | The Engine Run Time parameter is more than 20 seconds. |
| • | The Loop Status parameter is closed. |
| • | The Power Enrichment parameter is Active. |
Conditions for Setting the DTC
The PCM detects that the O2S 1 parameter is less than 300 mV for 5 seconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | 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 non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | The fuel pressure--System will run lean if the fuel pressure is too low. Monitor the fuel pressure while driving the vehicle at various road speeds and loads in order to confirm. Refer to Fuel System Diagnosis . |
| • | The MAP sensor--An output that causes the PCM to sense a lower than normal manifold pressure, or high vacuum, can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed or defaulted value for the MAP sensor. When the lean condition is gone when the sensor is disconnected, substitute a known good sensor and recheck. |
| • | A fuel contamination--Water, in even small amounts near the fuel pump inlet, can be delivered to the fuel injector. The water causes a lean exhaust condition. |
| • | The O2S harness--The O2S 1 pigtail may be mis-positioned and contacting the exhaust manifold. |
| • | An engine misfire--A misfire will result in unburned oxygen in the exhaust, which can cause a lean condition. Refer to Symptoms - Engine Controls . |
| • | A plugged fuel filter-- A plugged fuel filter can cause a lean condition. |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Is the O2S 1 voltage less than the value specified? | 52 mV | Go to Step 4 | Go to Step 3 | ||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||
4 |
Does the scan tool indicate that the O2S 1 voltage is within the specified values? | 351-551 mV | Go to Step 5 | Go to Step 6 | ||||||||||
5 | The O2S may be detecting a lean exhaust condition. Inspect for one of the following conditions:
Repair any of the above or similar engine conditions as necessary. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 | ||||||||||
6 | Test the O2S high signal circuit for a short to ground or a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 | ||||||||||
7 | Replace the O2S 1. Refer to Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||||
8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||||
9 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 10 | ||||||||||
10 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
