Exhaust Gas Recirculation: Testing and Inspection

Chart C-7:

EGR Solenoid Wiring Circuit:

CIRCUIT DESCRIPTION:
A properly operating EGR system will directly affect the air/fuel mixture requirements of the engine. Since the exhaust gas introduced into the air/fuel mixture cannot be used in combustion (contains very little oxygen), less fuel is required to maintain a correct air/fuel ratio. If the EGR system were to fail in a closed position, the exhaust gas would be replaced with air, and the air/fuel mixture would be leaner. The ECM would compensate for the lean condition be adding fuel, resulting in higher long term fuel trim values.

The fuel control in this engine is conducted within 4 block learn cells. Since EGR is not used at idle, the idle cell would not be affected by EGR system operation. The other fuel trim cells are affected by EGR operation, and when the EGR system is operating properly, the long term fuel trim values in all cells should be close to the same. If the EGR system becomes inoperative, the long term fuel trim values in the open throttle cells would change to compensate for the resulting lean mixtures, but the long term fuel trim value in the closed throttle cell would not change.

The difference in block learn values between the idle (closed throttle) cell and cell 2 is used to monitor EGR system preformance. When the difference between the two long term fuel trim values is greater than 12 and the long term fuel trim value in cell 2 is greater than 140, DTC 32 is set. The system operates in long term fuel trim cell 2 during a cruise condition at approximately 55 mph.

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

1. DTC's should be diagnosed using appropriate chart before preparing a functional check. If DTC's 14, 21, 23, 32, or 33 are set, use those charts first.

DIAGNOSTIC AIDS:
This chart is a functional check of the EGR system. If the EGR system works properly, check other items that could result in high long term fuel trim values in fuel trim cell 2, but not in the closed throttle fuel trim cell.