GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Canyon Pickup - 2WD 🢒 Engine 🢒 Engine Controls - 2.8L (LK5) 🢒 DTC P0121

Circuit Description

The powertrain control module (PCM) 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 mass air flow (MAF)
    • The engine RPM

If the PCM detects the airflow rate is more than expected, DTC P0121 sets.

Conditions for Running the DTC
    • DTCs P0641, P0651, P1516, P1523, P2101, P2176 are not set.
    • The engine is running and the engine speed is more than 600 RPM.

Conditions for Setting the DTC

The PCM detects that the calculated airflow rate is more than expected.

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.

Test Description

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

  1. This step will determine if the 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. When the PCM detects a condition within the TAC system other DTCs may set due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Keep this in mind when reviewing captured DTC info.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Are DTCs P0120, P0220, P1516, P1523, P2101, P2135 or P2176 also set?

--

Go to Diagnostic Trouble Code (DTC) List

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 Intermittent Conditions

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 9

Go to Step 5

5

  1. Allow the engine to reach operating temperature.
  2. Turn OFF all accessories.
  3. Observe the MAP sensor kPa parameter with a scan tool.

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

19-42 kPa

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
  1. Idle the engine.
  2. Take a snapshot of the Engine Data while performing the following action:
    3. • 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.
    • Refer to Scan Tool Snapshot Procedure in Wiring Systems.

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

--

Go to Step 8

Go to DTC P0101

8

    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 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 9

Go to Intermittent Conditions

9

  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 10

10

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK