GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC P1191

Circuit Description

The mass airflow (MAF) sensor measures the amount of air entering the engine during a given time. The engine control module (ECM) uses the MAF sensor information to monitor exhaust gas recirculation (EGR) flow rate. A large quantity of air entering the engine indicates an acceleration or high load situation, while a small quantity of air indicates deceleration or idle. The ECM has the ability to determine an intake leak by using the MAF sensor and the EGR control pressure sensor.

Conditions for Running the DTC
  1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0405, P0406, P0489, P0490, P0500, P1639, P2141, P2142, P2144, or P2145 are not set.
  2. The engine is running.
  3. The barometric pressure (BARO) sensor pressure is more than 72 kPa (10 psi).
  4. The battery charge is between 9-16 volts.
  5. The vehicle speed is less than 1.6 km/h (1 mph)
  6. The engine speed is between 600-700 RPM.
  7. The coolant temperature is between 0-80°C (32-176°F).

Conditions for Setting the DTC
    • The ECM detects an intake leak more than the calibrated value, internal to ECM.
    • The condition is met for 2 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • The most likely cause of the DTC is a leaking intake duct after the MAF sensor.
    • To run the diagnostic test the following conditions must be met:
       - The engine is at full operating temperature.
       - The vehicle is in drive.
       - The vehicle has been idling for more than 1 minute.
    • After meeting these conditions, shift the vehicle into park, and hold the engine speed steady between 1500-2100 RPM for 30 seconds. If the diagnostic test still fails to run, the vehicle must be driven.

Test Description

The number below refers to the step number on the diagnostic table.

  1. A large leak in the intake system will set a MAF sensor DTC. All intake ducts should be checked after the MAF sensor for proper installation.

DTC P1191

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Does the scan tool display any other DTCs set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Repair the air leak in one or more of the following components:
    3. • The air induction system after the MAF sensor
    • The intake gaskets
    • The EGR tower gasket

Did you complete the repair?

Go to Step 5

--

5
  1. Use a scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 6

Go to Step 2

6

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK