help diagnose EGR problem on '95 E320

[Glen]

The check engine light on my '95 S124 with 258K miles recently came on. Cleared code 5 from the DM (the only code). Every couple days the CEL and code 5 returns.

So, it looks like I have an EGR issue. I don't suspect the switch-over valves because they are only a few years old. A meter on the air pump connector and a cold start shows no power to the pump.

Where should I look next?

Thanks!