Home » GM 6.5 » GM/Detroit 6.5L ENGINE CONTROLS – DTC P0406 Exhaust Gas Recirculation (EGR) Position Sensor Circuit High Voltage

GM/Detroit 6.5L ENGINE CONTROLS – DTC P0406 Exhaust Gas Recirculation (EGR) Position Sensor Circuit High Voltage

Refer to Emission Hose Routing Diagram

Circuit Description
A EGR control pressure/baro sensor is used to monitor the amount of vacuum in the EGR circuit. It senses the actual vacuum in the EGR vacuum line and sends a signal back to the PCM. This signal is used to control EGR duty cycle calculated by the PCM. This is a type B DTC.

Conditions for Running the DTC
• The PCM performs this DTC diagnostic continuously.
• The ignition switch is in the ON position.

Conditions for Setting the DTC
• The EGR control pressure signal is greater than 3.96 volts (85 kPa).
• All diagnostic set conditions met for 2 seconds.

Action Taken When the DTC Sets
• The PCM will shut down the EGR.
• 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
With the ignition ON and the engine OFF, the manifold pressure is equal to atmospheric pressure with the signal voltage being high. This information is used by the PCM as an indicator of vehicle altitude. If DTC P0406 is intermittent, refer to Symptoms. 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, the 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.
2. This step will check for EGR Vent Solenoid DTC.
3. This step determines if DTC P0406 is a hard failure or an intermittent condition.
4. This step simulates conditions for a DTC P0405. If the PCM recognizes the change, the PCM and the signal circuit are OK.


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