GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Cobalt 🢒 Restraints 🢒 SIR 🢒 DTC P0068

Circuit 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

If the ECM detects the airflow rate is more than expected, DTC P0068 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0068 Throttle Body Airflow Performance

Conditions for Running the DTC
    • DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
    • The engine is running and the engine speed is more than 600 RPM.
    • DTC P0068 runs continuously when the above conditions are met.

Conditions for Setting the DTC
    • The ECM detects that the calculated airflow rate is more than expected.
    • The above condition is present for more than 0.2 second.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
    • 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
    • The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using a scan tool.

Diagnostic Aids
    • Inspect for the following conditions:
       - The throttle blade for damage
       - A skewed cam sensor signal--Inspect for signals that are intermittently shorted to ground, causing a fluctuating RPM on the scan tool.
    • If the condition is intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step will determine if the manifold absolute pressure (MAP) sensor voltage is within the proper range at idle.

    2.

  2. This step will determine if the MAP sensor responds properly to the change in manifold pressure.

    3.

  3. A throttle blade that sticks or binds may set this code. Opening the throttle through the entire range will indicate conditions such as these.

    4.

  4. When the ECM detects a condition within the ETC system, other DTCs may set due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Are any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition.
  3. Start the engine.
  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/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

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

Did you find and correct the condition?

--

Go to Step 8

Go to Step 5

5

  1. Allow the engine to reach operating temperature.
  2. Observe the MAP Sensor Voltage parameter with a scan tool.

Is the manifold absolute pressure (MAP) sensor voltage within the specified range?

0.8-4 V

Go to Step 6

Go to DTC P0106

6

  1. Idle the engine.
  2. Observe the MAP Sensor kPa parameter with a scan tool.
  3. Increase the engine speed slowly and then back to idle.

Does the MAP sensor kPa change smoothly and gradually as engine speed is increased and returned to idle?

--

Go to Step 7

Go to DTC P0106

7

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

  1. Inspect the throttle body for the following conditions while modulating the throttle through the entire range using the scan tool:
    2. • Loose or damaged throttle blade
    • Broken throttle shaft
    • Drive mechanism damage
  2. If any of these conditions exist, replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .

Did you find and correct the condition?

--

Go to Step 6

Go to Diagnostic Aids

8
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  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/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 7

9

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK