GM/Detroit 6.5L ENGINE CONTROLS – DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

Refer to Emission Hose Routing 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 f l ow rates. A large quantity of air entering the engine indicates an acceleration, high load situation or no EGR flow, while a small quantity of air indicates deceleration, idle or full EGR situations. The PCM will monitor MAF and EGR pressures at different ranges to determine correct EGR flow rates.

Conditions for Setting the DTC
• DTCs P0405, P0406, P0102 and P0103 not set.
• All MAF and EGR control pressure test complete (internal to PCM).
• EGR in Closed Loop.
• IAT greater than or equal to 20°C (68°F) and less than or equal to 95°C (203°F).
• Fuel rate between 10 and 25 mm3.
• Engine RPM between 1500 and 2100.
• Engine speed stable.

Conditions for Setting the DTC
• ALM cell s not changed for greater than 2 seconds.
• Above conditions persist for at least 3 seconds.

Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip 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 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
A vacuum leak will cause a DTC P1406. Carefully check all vacuum lines and components connected to the hoses for leaks or deformities. Check the vacuum source to the EGR solenoid assembly. Also check for a small leak in the EGR valve, and proper vacuum line routing. Vacuum line ends can be trimmed to ensure a tight fit if length permits. To run the diagnostic test the engine must be at the operating temperature with the vehicle in drive at idle for approximately 1 minute. Then, with the 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.
The Adaptive Learn Matrix (ALM) is used to adjust the EGR vacuum control based on mass air flow (MAF). The ALM may change as a result of back pressure increases over the life of the vehicle or other engine system variations. The ALM is made up of sixteen cells (numbered from zero to fifteen) in which each cell covers a range of engine speed (RPM) and load (mm3).

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
3. Vacuum lines should be checked carefully for proper fit and deformities.


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