Diagnostic Instructions
DTC Descriptors
DTC P0068: Throttle Body Airflow Performance
DTC P0121: Throttle Position (TP) Sensor Performance
Circuit/System Description
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
| • | The throttle position (TP) |
| • | The barometric pressure (BARO) |
| • | The manifold absolute pressure (MAP) |
| • | The intake air temperature (IAT) |
| • | The mass air flow (MAF) |
Conditions for Running the DTC
P0068
| • | DTC P0120, P0220, P0601, P0602, P0603, P0604, P0606, P0607, P060D, P1516, P2101, P2119, or P2176 is not set. |
| • | The DTC runs continuously when the above conditions are met. |
P0121
| • | DTC P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0335, or P0336 is not set. |
| • | The engine coolant temperature (ECT) is between 70-125°C (158-257°F). |
| • | The intake air temperature (IAT) is between -7 and +125°C (+19 and +257°F). |
| • | The DTC runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the airflow rate is more than the calculated airflow for more than 0.2 second.
Action Taken When the DTC Sets
| • | DTC P0068 is a Type A DTC. |
| • | DTC P0121 is a Type B DTC. |
| • | The control module commands the TAC system to operate in the Reduced Engine Power mode. |
Conditions for Clearing the MIL/DTC
| • | DTC P0068 is a Type A DTC. |
| • | DTC P0121 is a Type B DTC. |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Description and Operation
Throttle Actuator Control (TAC) System Description
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Circuit/System Testing
- Inspect for the following conditions:
| • | Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label |
| • | Inspect thoroughly for any type of leak or restriction |
| • | Air leaks at throttle body mounting area and intake manifold sealing surfaces |
- Allow the engine to reach operating temperature. Observe the MAP Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
| ⇒ | If more than 4 volts or less than 0.8 volt, refer to
DTC P0106
. |
- Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
| ⇒ | If the MAP sensor kPa does not change refer to
DTC P0106
. |
- Take a snapshot of the engine data list while performing the actions listed below. The mass air flow (MAF) sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.
| 4.2. | Increase the engine speed slowly to 3,000 RPM, then back to idle. |
| 4.3. | Exit from the snapshot and review the data. |
| 4.4. | Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle . |
| ⇒ | If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to
DTC P0101 or P1101
. |
- Inspect the throttle body for the following conditions:
| • | Loose or damaged throttle blade |
| • | Any throttle body damage |
| ⇒ | If any of these conditions exist, replace the throttle body assembly. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
