P0121

DTC P0068 or P0121

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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 actual throttle position and airflow rate is compared to an expected throttle position and airflow rate based on engine load. The engine control module (ECM) determines engine load based on inputs from the mass air flow (MAF) sensor and the manifold absolute pressure (MAP) sensor. Further comparisons are done to distinguish if a sensor is at fault, and the respective DTC will set.

The 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 supercharger inlet absolute pressure (SCIAP)
* The intake air temperature (IAT)
* The engine RPM

Conditions for Running the DTC

P0068
* DTCs P0122, P0123, P0220, P0221, P0222, P0223, P0601, P0602, P0603, P0604, P0606, P0607, P060D, P062F, P0641, P0651, P1516, P2101, P2119, P2135, P2176, P2610 are not set.
* The engine is running.
* DTC P0068 runs continuously when the above conditions are met.

P0121
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0116, P0128, P0122, P0123, P0220, P0221, P0222, P0223, P0335, P0336, P0401, P0405, P0601, P0602, P0603, P0604, P0606, P0607, P060D, P062F, P0641, P0651, P1404, P1516, P2101, P2119, P2135, P2176, P2610 are not set.
* The engine coolant temperature (ECT) is between 70-121°C (158-249°F).
* The engine IAT is between -7° and +60°C (+19° and +140°F).
* The engine speed is between 550-5,000 RPM.
* DTC P0121 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 DTC

* DTC P0068 is a Type A DTC.
* DTC P0121 is a Type B DTC.

Conditions for Clearing the MIL/DTC

* DTC P0068 is a Type A DTC.
* DTC P0121 is a Type B DTC.

Circuit/System Verification

1. If DTCs P0101, P0106, P0120, P012B, and P0220 are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis. Diagnostic Trouble Code Descriptions
2. Ignition ON, observe the scan tool BARO, MAP, and the SC Inlet Pressure sensor parameters. The readings should be within the range specified for your altitude. Determine the altitude at your current location and refer to Altitude Versus Barometric Pressure.
3. Engine running, observe the DTC information with a scan tool. DTCs P0068 or P0121 should not set.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame Records data.

Circuit/System Testing

Important: You must perform the Circuit/System Verification before proceeding with the Circuit/System Testing.

1. Start the engine. The Manifold Absolute Pressure (MAP) and SC Inlet Pressure Sensor parameters should decrease and closely match each other.

• If the MAP sensor parameter does not decrease, refer to DTC P0106. P0106
• If the SC Inlet Pressure Sensor parameter does not decrease, refer to DTC P012B. P012B

2. Engine running, inspect for any of the following conditions:

* Vacuum hoses for splits, leaks, and improper connections
* Air leaks at throttle body mounting area and intake manifold sealing surfaces
* A supercharger bypass valve that is binding or incorrectly adjusted-Refer to Supercharger Cleaning and Inspection Overhaul

• If any of the above conditions are found, repair as necessary.

3. While taking a snapshot of the engine data list, perform the following actions. Idle the engine. Increase the engine speed slowly to 3,000 RPM, then return to an idle. Observe the Mass Air flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor parameter should change smoothly as the engine speed is increased and is returned to idle.

• If the MAF sensor parameter does not change smoothly as the engine speed is increased and is returned to idle, refer to DTC P0101 or P1101. P0101 P1101

4. Ignition ON, slowly depress the accelerator pedal to a WOT position, then slowly release the pedal while comparing the TP Sensor 1 and TP Sensor 2 parameters. The difference between the parameters should be less than 4 percent.

• If TP Sensor 1 and TP Sensor 2 parameters differ more than 4 percent, refer to DTC P0120, P0122, P0123, P0220, P0222, P0223, or P2135. P0120 P0122 P0123 P0220 P0222 P0223 P2135

Caution: Turn OFF the ignition before inserting fingers into the throttle bore. Unexpected movement of the throttle blade could cause personal injury.

5. Ignition OFF, 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 after completing the diagnostic procedure. Verification Tests

* Throttle Body Assembly Replacement
* Control Module References for ECM replacement, setup, and programming Programming and Relearning