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, or 0 percent. If the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128, that is, from 0 percent to 100 percent. If you detect a rich condition, the fuel trim values will be below 128, or from 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 Setting the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0401, P0503, P0506, P0507, P0601, P1133, P1336, P1404, and P1441 are not set. |
| • | The Intake Air Temperature (IAT) is between -25°C (-13°F) and 115°C (175°F). |
| • | The Engine Coolant temperature is between 60°C (140°F) and 115°C (239°F). |
| • | The engine speed is between 550 RPM and 3400 RPM. |
| • | The vehicle speed is below 70 mph (113 km/h). |
| • | The MAP is above 27 kPa. |
| • | The BARO is greater than 74 kPa. |
| • | The EVAP purge is not occurring. |
| • | The Fuel Trim Index is below 75 (-54 percent). |
| • | The above conditions are present for 4 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 80 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. |
| • | Clear the MIL/DTCs with a scan tool. |
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. |
| • | Contaminated crankcase |
| • | If a DTC P1404 is also set, check the 5 V reference circuits for a short to voltage. |
| • | Check for a restricted intake manifold. |
| • | Check for a restricted exhaust system. |
| • | A shorted 5 V reference circuit may cause a DTC P0172 to set. Check the 5 V reference sensors for abnormal readings. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The Powertrain OBD System Check prompts the technician to complete some 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 fault occurred. The information is then stored on the scan tool for later reference.
-
A clogged air cleaner filter element restricts the airflow coming into the engine. This step checks the condition of the air cleaner filter.
-
A leaky injector can cause a rich condition and set DTC P0172. Refer to Fuel Injector Solenoid Coil Test for further diagnosis.
-
A loose TP sensor may not set a TP sensor related DTC, but may cause the system to become rich by a higher than actual TP reading.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
2 | Are any component related DTCs set? | -- | Go to Component DTC table | |
3 |
Is the Fuel Trim Index above the specified value? | 75 | ||
4 |
Is the Fuel Trim Index above the specified value while operating under the specified conditions. | 75 | ||
Did the air cleaner filter require replacement? | -- | |||
6 |
Did the air intake system require repair? | -- | ||
7 | Inspect the throttle body inlet for damage or foreign objects which may partially block the airflow and correct any problem found. Did the inspection of the throttle body reveal a condition requiring a repair or replacement? | -- | ||
8 |
Did the inspection reveal a condition requiring a repair? | -- | ||
9 | Start the engine with the vehicle in park or neutral and A/C OFF and note the idle quality. Is a low or unsteady idle being experienced? | -- | ||
10 | With the engine idling. Are the IAC counts below the specified value? | 100 | ||
11 |
Does the Fuel Trim Index increase above the specified value? | 60 | ||
12 |
Did the inspection reveal a condition requiring a repair? | -- | ||
13 |
Did the inspection reveal a condition requiring a repair? | -- | ||
14 |
Does the throttle position display increase steadily and evenly from its minimum voltage at closed throttle to its maximum voltage at wide-open throttle? | -- | ||
15 |
Did the table isolate a problem requiring a repair? | -- | ||
16 |
Was a problem isolated that requiring a repair? | -- | ||
Did the table isolate a problem requiring a repair? | -- | |||
18 |
Was contamination present? | -- | Go to Diagnostic Aids | |
Is the action complete? | -- | -- | ||
20 | Replace the MAP sensor. Is the action complete? | -- | -- | |
21 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||
22 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
