System Description
In order to provide the best possible combination of driveability, fuel economy, and emission control, a Closed Loop air and fuel metering system is used. While in a Closed Loop, the PCM monitors the oxygen sensor signal voltage. The PCM adjusts fuel delivery based on signal voltage. The long and the short term fuel trim values will indicate a change made to the fuel delivery system. The ideal fuel trim values are around 128 (0 percent). Whenever the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0 to 100 percent). Whenever a rich condition is detected, the fuel trim values will read below 128 (0 to -100 percent), indicating that the PCM is reducing the amount of fuel. Whenever the exhaust emissions reach an excessive level due to a lean 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, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0506, P0507, P0601, P1404, 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 750 RPM and 3400 RPM. |
| • | Vehicle speed is below 70 mph (113 km/h). |
| • | MAP is above 27 kPa. |
| • | BARO is greater than 73.8 kPa. |
| • | EVAP purge is not occurring. |
| • | Fuel Trim Index is above 160 (29%). |
| • | Above conditions present for over 4 seconds. |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) illuminates if the fault is active within the same conditions for 2 out of 80 ignition cycles. |
| OR |
| • | The MIL will illuminates after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | A scan tool can clear the DTCs. |
Diagnostic Aids
| • | Check for a poor connection at the PCM. Inspect harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| • | Check for a damaged harness. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the connectors and wiring harness related to the engine harness. A change in the display will indicate the location of the fault. |
| • | Check the brake power booster check valve. |
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 malfunction occurred. The information is then stored on the scan tool for later reference.
-
Visually/physically checking items which may cause a lean condition may determine the cause of the DTC being set and save diagnosis time.
-
A vacuum leak can change the Fuel Trim Index and set DTC P0171. This step checks the intake manifold for vacuum leaks.
-
Contaminants in fuel, such as alcohol or water, can create a lean condition setting DTC P0171. Checking for these contaminants could identify the malfunction.
-
If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||||||||||||||
2 | Are any component related DTCs set? | -- | Go to Component DTC tables | |||||||||||||
3 |
Is the Fuel Trim Index below the specified value? | 160 | ||||||||||||||
4 |
Does the Fuel Trim Index go below the specified value while operating under the specified conditions? | 160 | ||||||||||||||
Preliminary checks-visually/physically check the following items:
Did any of the above checks isolate a condition requiring repair? | -- | |||||||||||||||
6 |
Is the Fuel Trim Index below the specified value? | 160 | ||||||||||||||
7 |
Is the Fuel Trim Index below the specified value? | 160 | ||||||||||||||
8 | Lean condition is not present. Does a driveability problem exist? | -- | Go to Symptoms | |||||||||||||
Did any of the above checks isolate a condition requiring a repair? | -- | |||||||||||||||
10 | Turn the ignition switch ON, with the engine idling. Are the IAC counts above the specified value? | 5 | ||||||||||||||
Check the fuel for excessive water, alcohol, or other contaminants and correct the contaminated fuel condition if present. Was the fuel contaminated? | -- | |||||||||||||||
12 |
Was a repair necessary? | -- | ||||||||||||||
13 |
Is the fuel pressure steady and does the fuel pressure hold? | -- | Go to | |||||||||||||
14 |
Does the fuel pressure drop by the indicated value? | 21-69 kPa (3-10 psi) | Go to Fuel Injector Solenoid Coil Test (ECT Within 10C-35C (50F-95F) | Go to Fuel System Diagnosis | ||||||||||||
15 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Is the action complete? | -- | -- | |||||||||||||
16 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||||||||||||||
Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK Refer to Diagnostic Aids |
