Circuit Description
The powertrain control module (PCM) uses the following readings in order to calculate the predicted mass air flow (MAF) rate:
| • | The throttle position (TP) |
| • | The barometric (BARO) pressure |
| • | The intake air temperature (IAT) |
| • | The engine revolutions per minute (RPM) |
The PCM compares the predicted MAF value to the actual MAF value, and to the speed density calculation in order to verify the proper throttle operation.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0068 Throttle Body Air Flow Performance
Conditions for Running the DTC
| • | DTCs P0601, P0602, P0604, P0606, P1516, P2101, P2108 or U0107 are not set. |
| • | DTCs P0120 and P0220 are not active at the same time. |
| • | The engine operates longer than 1 second. |
| • | The engine speed is greater than 500 RPM. |
| • | This diagnostic runs continuously when the above conditions are met. |
Conditions for Setting the DTC
| • | The PCM detects that the difference between the actual MAF and the speed density calculated air flow is greater than expected. |
| • | All of the above conditions met for less than 1 second. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records. |
| • | The control module commands the TAC system to operate in the Reduced Engine Power mode. |
| • | A message center or an indicator displays Reduced Engine Power. |
| • | Under certain conditions the control module commands the engine OFF. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | 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 emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Inspect the throttle blade for being broken, bent, or missing. |
| • | Inspect the TP sensor for proper installation. A sensor that is mis-aligned could set this DTC. |
| • | Inspect the throttle actuator control (TAC) module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing. |
| • | Physically and visually inspect the throttle body assembly and correct any problems that you observe. Manually move the throttle blade from closed to wide open throttle (WOT). You should not need to use excess force. The throttle blade should move smoothly through the full range and then should independently return to a slightly open position. |
| • | When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info. |
| • | For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections . |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | 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 - Vehicle? | Go to Step 2 | |||||
2 | Is DTC P0101, P0102, P0103, P0107, P0108, P0112, P0113, P1111, or P1112 set? | Go to Step 3 | |||||
3 |
Important: If any of the conditions listed below exist, replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Inspect the throttle body for the following:
Did you find and correct the condition? | Go to Step 4 | Go to Diagnostic Aids | ||||
4 |
Does the DTC run and pass? | Go to Step 5 | Go to Step 2 | ||||
With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | ||||||
