P0068

°

DTC P0068 or P0121

Diagnostic Instructions

* Perform The Diagnostic System Check - Vehicle Initial Inspection and Diagnostic Overview
* Strategy Based Diagnosis
* Diagnostic Procedure Instructions

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 MAP
* 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, P060D, P062F, P0606, P0652, P0653, P1516, P2101, P2119, P2135, P2176 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, P060D, P062F, P0606, P0652, P0653, P1404, P1516, P2101, P2119, P2135, P2176 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 the DTC Sets

P0068
* 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.
* 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

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

Circuit/System Verification

1. If DTCs P0101, P0106, or P0120 are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis. Diagnostic Trouble Code Descriptions
2. Ignition ON, observe the scan tool MAP sensor parameter. The MAP sensor parameter should be within the range specified for your altitude. Determine the altitude at your current location and refer to Altitude Versus Barometric Pressure.

Circuit/System Testing

1. 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.

2. Engine running, inspect for the entire air induction system following conditions:

* Vacuum hoses for splits, leaks, and proper connections as shown on Vehicle Emission Control Information label
* Air leaks at throttle body mounting area and intake manifold sealing surfaces

3. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. The voltage should be between 0.8-4 volts.

• If more than 4 volts or less than 0.8 volt, refer to DTC P0106. P0106

4. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly to 3,000 RPM, then return the engine speed to a stabilized idle. The MAP sensor kPa parameter should change smoothly as the engine speed is increased and returned to idle.

• If the MAP sensor kPa parameter does not change, refer to DTC P0106. P0106

5. Take a snapshot of the engine data list while performing the actions listed below. The MAF sensor parameter should change smoothly as the engine speed is increased and returned to an idle.
6. Idle the engine.
7. Increase the engine speed slowly to 3,000 RPM, then return to an idle.
8. 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

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