System Description
A Closed Loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy, and emission control. While in a Closed Loop operation, the Powertrain Control Module (PCM) monitors the oxygen sensor signal voltage and adjusts the fuel delivery based on the signal voltage. The long term fuel trim values and the short term fuel trim values can indicate any changes to the fuel delivery. Monitor the scan tool for these changes. The ideal fuel trim values are around 128 (0 percent). If the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0 percent to 100 percent). If you detect a rich condition, the fuel trim values will be below 128 (0 percent to -100 percent), indicating that the PCM is reducing the amount of fuel delivered. If the exhaust emissions reach an excessive level due to a lean or a rich condition, a fuel trim DTC is set.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201, P0202, P0203, P0204, P0300, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, and P1441 not set. |
| • | Intake air temperature (IAT) is between -25°C (-13°F) and 115°C (175°F). |
| • | Engine coolant temperature is between 60°C (140°F) and 115°C (239°F). |
| • | Engine speed is between 550 RPM and 3400 RPM. |
| • | Vehicle speed is below 116 km/h (72 mph). |
| • | MAP is above 26 kPa |
| • | BARO is more than 72 kPa |
| • | EVAP purge is not occurring |
Conditions for Setting the DTC
| • | Fuel Trim Index is below 70 (-46 percent). |
| • | Above conditions present for over 16 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles. |
| Or |
| • | The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | 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 will store. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed. |
| • | A history DTC clears after 40 consecutive warm up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the long term fuel trim to 128 (0 percent).
| • | Check for a poor electrical connection at the PCM. Inspect the harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed electrical connectors |
| - | Damaged terminals |
| - | A poor terminal to wire connection |
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the electrical connectors and the wiring harness related to the engine harness. A change in the display will indicate the location of the malfunction. |
| • | Test for a contaminated crankcase. |
| • | Inspect for a restricted intake manifold. |
| • | Inspect for a restricted exhaust system. |
| • | A shorted 5 volt reference circuit may cause a DTC P0172 to set. Test the 5 volt reference sensors for abnormal readings. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
A clogged air cleaner filter element restricts the airflow coming into the engine. This step inspects the condition of the air cleaner filter.
-
A leaky fuel injector can cause a rich condition and set DTC P0172.
-
A loose TP sensor may not set a TP sensor related DTC, but could cause the system to become rich by a higher than actual TP reading.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
2 |
Are any component related DTCs set? | -- | ||||||||
3 |
Is the Fuel Trim Index above the specified value? | -46% | ||||||||
4 |
Is the Fuel Trim Index above the specified value while operating under the specified conditions? | -46% | ||||||||
Did the air cleaner filter require a replacement? | -- | |||||||||
6 |
Did you find and correct the condition? | -- | ||||||||
7 |
Did the inspection of the throttle body reveal a condition requiring a repair or a replacement? | -- | ||||||||
8 |
Did you find and correct the condition? | -- | ||||||||
9 |
Is the engine experiencing a low or an unsteady idle? | -- | ||||||||
10 |
Are the IAC counts below the specified value? | 100 | ||||||||
11 |
Does the Fuel Trim Index increase above the specified value? | -46% | ||||||||
12 |
Did you find and correct the condition? | -- | ||||||||
13 |
Did the fuel pressure regulator require a replacement? | -- | ||||||||
14 |
Does the throttle position display increase steadily and evenly from the minimum voltage at closed throttle to the maximum voltage at wide-open throttle? | -- | ||||||||
15 |
Did you find and correct the condition? | -- | ||||||||
16 |
Did you find and correct he condition? | -- | ||||||||
Did you find and correct the condition? | -- | |||||||||
18 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Was there contamination present? | -- | Go to Diagnostic Aids | |||||||
Did you complete replacement? | -- | -- | ||||||||
20 |
Did you complete the replacement? | -- | -- | |||||||
21 |
Does the DTC rest? | -- | System OK |
