P0121
DTC P0068 or P0121
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
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 engine RPM
* The mass air flow (MAF)
Conditions for Running the DTC
P0068
* The engine is running.
* 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
* The engine is running.
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0335, or P0336 are 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 greater than the calculated airflow for greater 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 ECM 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 (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Throttle Actuator Control (TAC) System Description (Throttle Actuator Control (TAC) System Description)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
1. 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
* Inspect throttle body for dirt, debris, and coking. Refer to Throttle Body Inspection and Cleaning (Throttle Body Inspection and Cleaning).
2. Allow the engine to reach operating temperature. Observe the MAP Sensor Voltage parameter with a scan tool. Voltage should be greater than 0.8 volt and less than 4 volts.
• If greater than 4 volts or less than 0.8 volt, refer to DTC P0106 (P0106).
3. 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 (P0106).
4. 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.
1. Idle the engine.
2. Increase the engine speed slowly to 3,000 RPM, then back to idle.
3. Exit from the snapshot and review the data.
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 returned to idle.
• If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and returned to idle refer to DTC P0101 or P1101 (P0101).
5. Inspect the throttle body for the following conditions:
* Loose or damaged throttle blade
* Broken throttle shaft
* Any throttle body damage
• If any of these conditions exist, replace the throttle body assembly.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Air Cleaner Element Replacement (Service and Repair)
* Air Cleaner Outlet Duct Replacement (Air Cleaner Outlet Duct Replacement)
* Lower Intake Manifold Replacement (Service and Repair)
* Manifold Absolute Pressure Sensor Replacement (Service and Repair)
* Mass Airflow Sensor with Intake Air Temperature Sensor Replacement (Service and Repair)
* Throttle Body Assembly Replacement (Removal and Replacement)
* Upper Intake Manifold Replacement (Service and Repair)