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Here is the diagnostic routine from the factory service manual for this code:
SET CONDITION Conditions are met, the EGR is turned OFF and ON momentarily. The O2 Sensor signal is monitor for changes in its output signal during this test. If no significant change or too much change is seen, a flag is set
It would appear that the PCM determines that the EGR system is not operating by looking for the front )2 sensor signal to momentarily drop low (lean) when the valve is commanded open during the self test it runs periodically on the system. This could also be due to clogged EGR passages in the manifold; try using a vacuum pump to manually open the valve at idle; this chould cause the engine to stall from the resulting huge vacuum leak. If it does not, either the valve is not operable (not opening) or the EGR passages in the engine are clogged with carbon; if so, the intake manifold will need to be removed for manual cleaning.
I hope this is helpful; if so, an accept would be most appreciated! thanks!