Code P048, EGR System Malfunction: Notes

This code test checks for an EGR system fault. After engine is fully warm and EGR system has been operating on full for a period of time, PCM will disable EGR valve and monitor change in rear short term fuel trim for next 5 seconds. If change is 14 counts or greater, EGR system is functioning normally and will not be retested for current ignition cycle. If change is less than 14 counts, test is failed and counter is incremented. Code P048 will set when counter reaches 3.

The counter is decremented if at any time before the counter reaches 3, a change in rear short term fuel trim is 14 counts or greater. If counter reaches zero, 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 EGR system is functioning and PCM does not have the ability to turn it off.