P0406

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Steps 4 - 8:

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Steps 13 - 15:

DTC P0406 Exhaust Gas Recirculation (EGR) Sensor Circuit High




Circuit Description
An Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures. It accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, combustion temperatures are reduced

A linear EGR valve is used on this system. The linear EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The valve controls exhaust flow going into the intake manifold form the exhaust manifold through an orifice with a PCM controlled pintle. The PCM controls the pintle position using inputs from the Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensors. The PCM then commands the EGR valve to operate when necessary by controlling an ignition signal through the PCM. This can be monitored on a Tech 2 as the Desired EGR Position.

The PCM monitors the results of its command through a feedback signal. By sending a 5 volt reference and a ground to the EGR valve, a voltage signal representing the EGR valve pintle position is sent to the PCM. This feedback signal can also be monitored on a Tech 2 and is the actual position of the EGR pintle. The Actual EGR Position should always be near the commanded or Desired EGR Position.

If the PCM detects a continuous short to ground in the signal circuit or the sensor, then DTC P0406 will set. Diagnostic Trouble Code P0406 is a type A code.

Conditions for Setting the DTC
- IAT is greater than 5 °C (41 °F).
- The PCM sees less than 0.10 voltage from the EGR valve sensor.
- A malfunction is present for 10 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM will record operating conditions at the time the diagnostic fails.
- A history Diagnostic Trouble Code is stored.
- The EGR Valve is disabled.

Conditions for Clearing the MIL/DTC
- The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history Diagnostic Trouble Code will clear after 40 consecutive warm-up cycles without a fault.
- Diagnostic Trouble Code(s) can be cleared by using the Tech 2.

Diagnostic Aids
Due to the moisture associated with exhaust systems, the EGR valve may freeze and stick in colder
weather at times. After the vehicle is brought into a warm shop for repairs, the valve warms and the problem disappears. By watching the Actual EGR and Desired EGR Positions on a cold vehicle with a Tech 2, the fault can be verified easily. Check the freeze frame data to determine if the Diagnostic Trouble Code set when the vehicle was cold by viewing the Engine Coolant Temperature (ECT).