GM/Detroit 6.5L ENGINE CONTROLS – DTC P1191 Intake Air Duct Leak

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/BARO sensor.

Conditions for Running 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).

Conditions for Setting the DTC
• 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 clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The 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.


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