The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by decreasing combustion temperature.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture thus diluted, combustion temperatures are reduced.

The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The feedback signal can be monitored with a scan tool as ACTUAL EGR POS. ACTUAL EGR POS should always be near the commanded EGR position ( DESIRED EGR POS ). If a problem with the EGR system will not allow the PCM to control pintle position properly, DTC P1406 should set. The PCM also tests for EGR flow; if incorrect flow is detected, DTC P0401 should set. If DTC P0401 and/or DTC P1406 are encountered, refer to the diagnostic chart(s).

The linear EGR valve is usually activated under the following conditions:

The PCM monitors EGR actual position and adjusts pintle position accordingly. The PCM uses information from the following sensors to control the pintle position:

An EGR flow check diagnosis of the linear EGR system is covered by DTC P0401. Pintle position error diagnosis is covered by DTC P1406. If EGR diagnostic trouble codes P0401 and/or P1406 are encountered, refer to the applicable DTC chart for diagnosis.

Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause: