Yellen calls the shots on Wednesday

The bond market is starting to get cold feet about the Fed.

So for traders, appearances by Fed Chair Janet Yellen both Wednesday and Thursday could be critical in setting market expectations about the course of Fed rate hikes. Also looming large is Friday's jobs report, the last big piece of data ahead of the Fed's Dec. 16 meeting, so Wednesday's November ADP payroll report will also be important to markets.

The shockingly weak November ISM manufacturing survey Tuesday showed a contraction in the manufacturing sector for the first time in three years. The reading was the latest piece of softish data that raises doubts about the Fed's plan to raise rates in December, if the economy is strong enough.

"We're going to pay a lot of attention because she's going to have more insight than the rest of us. Let's see how confident she is," said David Ader, head of Treasury strategy at CRT Capital. "Maybe there's concern that the Fed is doing this (rate hike) because they're committed to it, and the economy is just not that strong. And I think that may not get people to be aggressive buyers, but it certainly is inhibiting people being aggressive sellers."

Yellen is scheduled to speak at the Economics Club of Washington on Wednesday at 12:25 p.m. ET and then testifies the next morning before the Congressional Joint Economic Committee. On the data front, there is the ADP data at 8:15 a.m. ET, and 192,000 private sector payrolls are expected. That compares with expectations of 200,000 for Friday's November government jobs report.

There are also productivity and costs at 8:30 a.m. and the Fed's beige book on the economy at 2 p.m.