OK, new code on one of our vans turned up. The code that I just fixed (hopefully) was an EGR flow code. Replaced the DPFE and it hasn't been back yet, but today it showed a p1157. This is "Lack of Downstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2".
Is this a common failure? I didn't find much here, but one thing that I found is an exhaust leak can cause this code. What is most likely? An exhaust leak, the sensor or wiring?
I looked at Freeze Frame and found STFT for bank #2 was at 12.X. What does this suggest?