P1191

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The Mass Air Flow (MAF) sensor measures the amount of air entering the engine during a given time. The PCM uses the mass air flow information to monitor EGR flow rates. 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 PCM has the ability to determine a intake leak by using the Mass Air Flow (MAF) sensor and the EGR Control Pressure/Barometric pressure (BARO) sensor.


Conditions for Setting the DTC

^ The PCM performs this DTC diagnostic continuously.

^ The DTCs P0405, P0406, P0102 and P0103 are not set.

^ Baro greater than 75 kPa.

^ All EGR tests have been completed (internal to PCM).

^ Intake leak greater than calibrated value (internal to PCM)

^ All of the diagnostic set conditions met for 2 seconds.


Action Taken When the DTC Sets

^ The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL off after three consecutive trips without a fault condition.

^ A History DTC will clear when forty consecutive warm-up cycles that the diagnostic does not fail (coolant temperature has risen 5°C (40°F) from start up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle.

^ Use of a Scan tool

Diagnostic Aids

The most likely cause of failure is a leaky intake

duct after the MAF sensor.

To run the diagnostic test the engine must be at operating temperature, vehicle in drive at idle for approximately 1 minute, then with vehicle in park hold engine rpm steady between 1500 and 2100 rpm for 30 seconds. If the diagnostic test fails to run, vehicle must be driven.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

3. A large leak in the intake system will set MAF sensor DTC. All intake ducts should be checked after the MAF sensor.