You can check the actual line status of the V.35 interface using the /usr/sbin/wanpipemon command:
[root@host cdrouter]# /usr/sbin/wanpipemon -i wp1chdlc -u 9000 -c xm
Network interface running Cisco HDLC protocol...
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MODEM STATUS
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DCD: High
CTS: High
[root@host cdrouter]# /usr/sbin/wanpipemon -i wp1chdlc -u 9000 -c xl
Network interface running Cisco HDLC protocol...
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LINK STATUS
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Link status: Active
Available data frames for application: 0
Receiver status: Enabled