Computer Command Control - Throttle Body Fuel Injection

Chart C-7:

EGR Wiring Diagram:

CIRCUIT DESCRIPTION:

The ECM operates a vacuum solenoid to control the EGR valve. The solenoid is normally closed. The ECM provides a ground path to energize the solenoid. This allows vacuum to flow to the EGR valve. The ECM controls the operation of the EGR valve based on input from the following sensors:

1. The Coolant Temperature Sensor (CTS) sensed a temperature value above 25~C (77~F).
2. The Throttle Position Sensor (TPS) sensed an off idle condition.
3. The Manifold Absolute Pressure (MAP) sensor is sending the proper signal to the ECM.




TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. Grounding the diagnostic test terminal should allow the EGR solenoid to energize, and vacuum should flow to the EGR valve.
2. When the diagnostic test terminal is not grounded, the vacuum should bleed off through a vent in the EGR solenoid, and the EGR valve should close.
3. This test determines if the electrical control portion of the system is at fault, or if the EGR solenoid and/or connector is at fault.
4. This system uses a negative back pressure EGR valve which should hold vacuum when the engine is not running.
5. Once vacuum has been applied to the valve, start the engine and note EGR diaphragm movement. Vacuum should bleed off and the EGR valve should close.

NOTE: Once the test sequence is completed, clear codes and verify NO "SERVICE ENGINE SOON" light exists.




DIAGNOSTIC AIDS:

1. Vacuum hoses should be thoroughly inspected for internal restrictions in the EGR system.
2. The ECM uses the Manifold Absolute Pressure (MAP) sensor for checking EGR operation.
3. Remove the EGR valve.
4. Plug the exhaust side hole with a suitable stopper. Leaving the intake side hole open, attempt to start the engine. If the engine runs at a high idle (up to 3000 rpm is possible) or starts and stalls, the EGR intake passage is not restricted. If the engine starts and idles normally, the EGR intake passage is restricted.
5. Remove the stopper from the exhaust hole and plug the intake passage. With the exhaust side hole open, start the engine and check for the presence of exhaust gases. If no exhaust gas is present, the EGR exhaust passage is restricted.
6. If no problems are found, see DIAGNOSIS BY SYMPTOM.