GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2008 🢒 Astra 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0068, P0121, or P0221

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • 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 1 Performance

DTC P0221: Throttle Position (TP) Sensor 2 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 intake air temperature (IAT)
    • The engine RPM
    • The mass air flow (MAF)

Conditions for Running the DTC
    • DTCs P000A, P000B, P0016, P0017, P0102, P0103, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0221, P0222, P0223, P0340, P0341, P0365, P0366, P0458, P0459, P0642, P0643, P0652, P0653, P065E, P2227, P2228, P2229 are not set.
    • DTCs P0068, P0121, P0221 run 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 B DTC.
    • DTCs P0121 and P0221 are Type A DTCs.
    • 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 B DTC.
    • DTCs P0121 and P0221 are Type A DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Throttle Actuator Control (TAC) System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
    • Verify that DTCs P0122, P0123, P0222, or P0223 are not set. Refer to DTC P0122, P0123, P0222, or P0223.
    • 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/Failure Records data.

Circuit/System Testing
  1. Inspect for the following conditions:
    2. • Vacuum hoses for splits, kinks, and proper connections
    • Inspect thoroughly for any type of leak or restriction.
    • Air leaks at throttle body mounting area and intake manifold sealing surfaces
  2. Ignition OFF for 90 seconds, determine the current vehicle testing altitude. Ignition ON, engine OFF, observe the scan tool BARO parameter. Compare the parameter to the Altitude Versus Barometric Pressure table. The BARO parameter should be within the specified range as indicated in the table.
    3. ⇒If the BARO parameter is not within the specified range as indicated in the table, refer to DTC P2227, P2228, or P2229.
  3. Take a snapshot of the engine data list while performing the actions listed below. The MAF sensor kg/h should increase as the engine speed is increased and decrease as the throttle is returned to idle.
    4. • Idle the engine.
    • Increase the engine speed slowly to 3,000 RPM, then back to idle.
    • Exit from the snapshot and review the data.
    • Observe the MAF Sensor parameter frame by frame with a scan tool. The MAF sensor kg/h should change smoothly and gradually as the engine speed is increased and is returned to idle.
         ⇒If the MAF sensor kg/h does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101.
  4. Inspect the throttle body for the following conditions:
    5. • 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.

    •  Throttle Body Assembly Replacement
    •  Control Module References for ECM replacement, setup, and programming