GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 Exhaust Gas Recirculation (EGR) System Description

EGR Valve
Object Number: 14441 Size: SH

Purpose

An exhaust gas recirculation (EGR) system is used in order to lower oxides of nitrogen (NOx) emission levels. The EGR system accomplishes this by feeding small amounts of exhaust gas back into the combustion chamber. High combustion temperatures cause NOx. Combustion temperatures are reduced when the air-fuel mixture is diluted with the exhaust gases.

Operation
Object Number: 11696 Size: SH
(1)Cap-Sensor
(2)Sensor-EGR Pintle Position
(3)Pole Piece-Primary
(4)Bobbin and Coil Assembly
(5)Sleeve-Armature
(6)Valve-Pintle
(7)Armature and Base Assembly

The EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The EGR valve controls the exhaust flow into the intake manifold from the exhaust manifold through an orifice with a powertrain control module (PCM) controlled pintle. The PCM controls the pintle position using inputs from the engine coolant temperature (ECT) sensor, the throttle position (TP) sensor, and the manifold absolute pressure (MAP) sensor. The PCM commands the EGR valve in order to supply the correct amount of exhaust gas recirculation for the current engine operating conditions. This can be monitored on a scan tool as the Desired EGR Position.

The PCM monitors the position of the EGR valve through a feedback signal. The PCM supplies 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 from the EGR valve. This feedback signal can also be monitored on a scan tool and is the actual position of the EGR pintle. The actual EGR position should always be near the commanded or desired EGR position.

The EGR valve is usually activated under the following conditions:

    • The engine is warm.
    • The engine is above the idle speed.

Diagnosis
Object Number: 11699 Size: SH
(1)Linear EGR Valve
(2)Exhaust Gas
(3)To Cylinders
(4)Pintle

Too much EGR flow causes any of the following conditions to occur:

    • The engine stalls after a cold start.
    • The engine stalls during closed throttle conditions.
    • The vehicle surges during a cruise condition.
    • A rough idle
    • A DTC P0300 misfire detected

Too little or no EGR flow allows the combustion temperatures to increase. This causes the following symptoms:

    • Spark knock, detonation
    • Engine overheating
    • Emission test failure
    • DTC  P0401
    • Poor fuel economy

The EGR flow diagnosis is included in the DTC P0401 diagnostic table. The EGR pintle position and the EGR valve control circuit diagnosis are covered in DTCs P0404, P0405, and P1404. Go to the appropriate DTC table for diagnosis if an EGR DTC is stored.