Component Tests and General Diagnostics

Chart C-7E - Pulse Width Modulated (PWM) EGR System Check:

Wiring Diagram for Chart C-7E - Pulse Width Modulated (PWM) EGR System Check:

CHART C-7E - PULSE WIDTH MODULATED (PWM) EGR SYSTEM CHECK


Circuit Description:

PWM EGR is an ECM control that pulses the vacuum signal to the EGR. This is accomplished through a normally open EGR solenoid which when energized by the ECM shuts off the vacuum to the EGR valve diaphragm. This system can pulse the solenoid many times per second (PWM). The EGR solenoid is always energized (EGR off) when any one of the following conditions are met:

^ Throttle Position greater than specified.

^ Coolant temperature less than specified.


Test Description:

1. Checks to see if the EGR passages are restricted or if the valve is stuck open.

2. A cold engine is simulated by disconnecting the coolant temperature sensor which will also energize the EGR solenoid.

3. With the 4 wire EST connector disconnected, the ECM thinks the engine is not running. Grounding the test terminal, under this condition, causes the ECM to pulse the EGR solenoid "ON" and "OFF" for testing which will result in a controlled vacuum supply to the EGR valve diaphragm at 2000 RPM.

4. By disconnecting EGR solenoid electrical connector, control by the ECM is overridden and the normally opened EGR solenoid will pass available vacuum. At 2000 RPM EGR valve should move if EGR control system is functioning properly.


5. If vacuum is below 23.6 kPa (7" Hg) at 2000 RPM with EGR solenoid electrical connector disconnected, a leak or restriction between test point (EGR diaphragm) and source is evident.

6. Checks EGR solenoid electrical control circuit. The test light should "flicker faintly" if the ECM, harness and connections are OK. "Flicker faintly" refers to a slightly pulsing glow as opposed to a "bright steady" glow from a continuous ground path.

Steps 1, 2, and 3 represent an EGR system operation check.