Circuit Description
When the vehicle is first started, the engine operates in an Open Loop operation, ignoring the oxygen sensor signal and calculating the air/fuel ratio based on inputs from the engine coolant temperature (ECT), the throttle position, and the manifold absolute pressure sensors only. The powertrain control module (PCM) will begin by using the oxygen sensor signal for controlling the fuel delivery (Closed Loop) when the following conditions are met:
| • | The engine has run a minimum amount of time based on ECT at engine start up. |
| • | The oxygen sensor (O2S 1) has a varying voltage output showing that it is hot enough to operate properly. |
| • | The ECT has increased a minimum amount based on the ECT at engine start up. |
Conditions For Running The DTC
| • | DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0131, P0132, P0134, P0201, P0202, P0203, P0204, P0300, P0336, P0440, P0442, P0446, P0601, P0602, P1441, or P1621 are not set. |
| • | Engine has been running more than 250 seconds for an auto trans, or 230 seconds for a manual trans. |
| • | Engine speed is between 1200 RPM and 3400 RPM. |
| • | The throttle position (TP) angle is between 10 percent and 40 percent. |
| • | ECT is more than 65°C (149°F). |
| • | Above conditions have been met for 2 seconds. |
Conditions For Setting The DTC
The engine is not in Closed Loop for 5 seconds out of 12.5 seconds.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | The MIL/DTCs can be cleared by using the scan tool. |
Diagnostic Aids
An O2 sensor performance or slow response DTC is most likely caused by one of the following items:
| • | Fuel pressure--The engine may run rich if the fuel pressure is too high. The PCM can compensate for some increase. However, if the fuel pressure is too high, a DTC P0172 may set. Refer to Fuel System Diagnosis . |
| • | Leaking injector--A leaking or malfunctioning injector can cause the system to go rich. |
| • | MAP sensor--An output that causes the PCM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. |
| • | Pressure regulator--Check for a restricted fuel pressure regulator return hose by checking for a damaged or kinked hose between the fuel filter and the fuel tank. |
| • | TP sensor--An intermittent TP sensor output can cause the system to go rich due to a false indication of the engine accelerating. |
| • | O2S 1 contamination--Inspect the O2S 1 for silicone contamination from fuel or the use of improper RTV sealant. The O2S 1 sensor may have a white powdery coating and result in a high but false voltage signal (rich exhaust indication). The PCM will then reduce the amount of fuel delivered to the engine causing a severe surge or driveability problem. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Powertrain On-Board Diagnostic (OBD) System Check prompts the technician to complete some of the basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information then stores in the scan tool for later reference.
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This step looks for the actual O2S 1 voltage output from the sensor, and the voltage read by the scan tool to have a similar range. If the voltages are similar the fault is caused by a damaged O2S 1 sensor. If the reading from the scan tool shows a small voltage change and the DMM shows a normal sweeping voltage, the PCM is unable to read the voltage correctly and will be replaced.
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Reprogram the replacement PCMs and perform the Crankshaft Position System Variation Procedure. Refer to the latest Techline information for PCM programming .
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 |
Were there any component DTCs set? | -- | Go to Component DTC tables | |
3 |
Does the loop status change from Closed to Open Loop on the scan tool? | -- | Go to Diagnostic Aids | |
4 | Visually and physically inspect the following items:
Did you find and correct a fault in any of the above conditions? | -- | ||
5 |
Is the resistance above the specified value? | 2 ohms | ||
6 |
Does the DMM indicate the specified value? | O L | ||
Does the voltage sweep on the scan tool and the voltage on the DMM follow a similar pattern? | -- | |||
8 | Check the connector terminals at the O2S 1 and PCM for corrosion or spread terminals. Repair as necessary. Was a repair made? | -- | ||
Is the action complete? | -- | -- | ||
10 | Repair the open or high resistance in the signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
11 |
Is the action complete? | -- | -- | |
12 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming Is the action complete? | -- | -- | |
13 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
14 | Check to see if any additional DTC are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK |
