Part 2 of 2

DTC 23 Chart Part 2 Of 2 Exhaust Gas Recirculation:

EGR Control Wiring Diagram:

Circuit Description:


The Exhaust Gas Recirculation (EGR) valve vacuum is controlled by an ECM controlled solenoid valve. The ECM will turn the EGR "ON" and "OFF" (Duty Cycle) by grounding CKT 435. The duty cycle is calculated by the ECM based on information from the engine coolant temperature, air flow and engine RPM. There should be no EGR when in park or neutral, TP sensor input below a specified value, or TP sensor indicating Wide Open Throttle (WOT).

With the ignition "ON" engine stopped, the EGR solenoid valve is de-energized and by grounding the diagnostic "test" terminal, the solenoid valve is energized.



The ECM will check EGR operation when:

- Vehicle speed is above 50 mph.
- Throttle angle is between 8% and 30%.
- No more than 0.4% change in throttle position.
- MAP is in the range listed below, depending on the barometric pressure (as measured by MAP sensor w/ign. "ON", engine "OFF".)

BARO PRESSURE (kPa)
100 90 80 70
________________________________

MAP 30-85 20-75 10-65 0-55
(RANGE)





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:


The EGR circuit can be inoperative if the PNP switch is misadjusted or faulty. The EGR is disabled when in park or neutral. To check the PNP switch, Chart C-1A Park/Neutral Switch Diagnosis

Suction from shop exhaust hoses can alter backpressure and may affect the operation of the EGR valve during install testing.

The ECM also monitors left side short term fuel trim during a DTC 32 test and must detect a change to pass the test. If short term fuel trim is at a fixed value (lean or rich) when a DTC 32 test is run, a DTC 32 may set.

Vacuum lines should be thoroughly checked for proper routing. Vacuum source goes to orifice side of the EGR solenoid valve. Refer to "Vehicle Emissions Control Information" label.