Part 2 of 2

Chart C-7 EGR System Check (Part 2 Of 2):

EGR System Wiring Circuit:

CIRCUIT DESCRIPTION:
The Exhaust Gas Recirculation (EGR) valve is controlled by a normally closed solenoid valve. The PCM turns the solenoid "ON" to allow vacuum to pass to the EGR, and turns the solenoid "OFF" to prevent EGR operation.

The duty cycle is calculated by the PCM based on information from the Throttle Position (TP) sensor, Engine Coolant Temperature (ECT) sensor, Manifold Absolute Pressure (MAP) sensor and engine speed. There should be no EGR when TP sensor input is below 3% or over 50% throttle, low vacuum or low engine coolant temperature.

With the ignition "ON" and engine "OFF," the EGR solenoid valve is de-energized. The solenoid valve, however, should be energized, if the diagnostic "test" terminal is grounded with the ignition "ON" and engine "OFF."

CHART TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The remaining test checks the ability of the EGR valve to interact with the exhaust system. This system uses a negative backpressure EGR valve which should hold vacuum with engine "OFF."
2. When engine is started, exhaust backpressure at the base of the EGR valve should open the valve's internal bleed and vent the applied vacuum allowing the valve to seat.

DIAGNOSTIC AIDS:
Suction from shop exhaust hoses can alter backpressure and may affect the functional check of the EGR valve.

During normal EGR valve operation, the movement of the EGR pintle is small. It is important to determine whether the valve pintle moves and not how much it moves.