Part 2 of 2

DTC P048:

EGR Valve Circuit:

CIRCUIT DESCRIPTION:
This diagnostic test is designed to check for an EGR system fault. After the engine is fully warmed up and the EGR system has been operating on full for a period of time, the PCM will disable the EGR solenoid and monitor the change in rear short term fuel trim for the next 5 seconds. If the change is 14 counts or greater, the EGR system is functioning normally and will not be retested for the current ignition cycle. If the change is less than 14 counts, the test is failed and the counter is incremented. When the counter reaches 4, Code P048 is set. If at any time before the counter reaches 4 a change in the rear short term fuel trim is 14 counts or greater the counter is decremented. If the counter reaches 0, the next rear short term fuel trim change of 14 counts or greater will pass the test for the entire ignition cycle. When Code P048 is set, either the EGR system was turned off before the test started or the EGR system is functioning and the PCM does not have the ability to turn it off.

NOTES ON FAULT TREE:
6. Checking CKT 750 and fuse "CS" for an open.
7. Checking if EGR valve is open circuited.
8. Checking if CKT 435 is open.
9. Checking if PCM is open internally or if CKT 435 is shorted to voltage.
10. EGR valve control circuits are OK. Checking to see if the EGR valve can respond correctly to the signal being sent to it from the PCM.