SLX V6-3.2L SOHC (1996)
EGR Valve: Description and Operation
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
EGR PURPOSE
The exhaust gas recirculation (EGR) system is used to reduce emission levels of oxides of nitrogen (NOx). NOx emission levels are caused by a
high combustion temperature. The EGR system lowers the NOx emission levels by decreasing the combustion temperature.
LINEAR EGR VALVE
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.
The fuel/air mixture will be diluted and combustion temperatures reduced.
LINEAR EGR CONTROL
The PCM monitors the EGR actual position and adjusts the pintle position accordingly. The PCM uses information from the following sensors to
control the pintle position:
^
Engine coolant temperature (ECT) sensor.
^
Throttle position (TP) sensor.
^
Mass air flow (MAF) sensor.
LINEAR EGR VALVE OPERATION AND RESULTS OF INCORRECT OPERATION
The linear EGR valve is designed to accurately supply EGR to the 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
the pintle position properly, DTC P1406 will set. The PCM also tests for EGR flow. If incorrect flow is detected, DTC P0401 will set. If DTCs
P0401 and/or P1406 are set, refer to the DTC charts.
The linear EGR valve is usually activated under the following conditions:
^
Warm engine operation.
^
Above-idle speed.
Too much EGR flow at idle, cruise or cold operation may cause any of the following conditions to occur:
^
Engine stalls after a cold start.
^
Engine stalls at idle after deceleration.
^
Vehicle surges during cruise.
^
Rough idle.
^
DTC P0300 (misfire detected).
Too little or no EGR flow may allow combustion temperatures to get too high. This could cause:
^
Spark knock (detonation).
^
Engine overheating.
^
Emission test failure.
^
DTC P0401 (EGR flow test).
^
Poor fuel economy.
