Fan Assembly Module (UBR10-FAN-ASSY=)

that fan module was EOLed and likely was removed from supported hardware in more current IOSes

http://www.cisco.com/c/en/us/products/collateral/video/ubr10000-series-u...

it was replaced with the UBR10012-FAN-PLUS

here is an excerpt from the docs http://www.cisco.com/c/en/us/td/docs/cable/cmts/ubr10012/installation/fi...

Fan Assembly Module (UBR10012-FAN-PLUS=)

This fan assembly as shown in Figure 2 has nine internal fans that draw cooling air into the front of the chassis and directs it across the internal components. This fan assembly module provides:
Increased cooling capability
Higher redundancy in case of a failure
Repositioned thermal sensor that detects the ambient temperature of the cable plant or facility and adjusts the variable fan speeds to maintain the temperature
Figure 2 Fan Assembly Module (UBR10012-FAN-PLUS=)

1
Fan assembly module
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This fan assembly module works at four variable speed levels (0, 1, 2, and 3). The operating speed of the fan is determined by the temperature of the facility. A thermistor, mounted on the fan assembly module, is placed in front of the vent holes on the front panel. It measures the ambient air temperature on the outside of the fan module. The threshold temperatures and speed levels are set internally and the fan assembly controller monitors the thermistor and controls the speed of the fan. When powered on, the fans operate at a speed according to the ambient average air temperature of the facility at the appropriate speed level.

Note Each speed level is based on a certain system pressure drop. As the system pressure changes, the air flow rate also changes.

Note On startup, it may take up to 30 seconds for the fans to stabilize at the appropriate speed.
Three LEDs indicate the status of the fan assembly. Table 1 lists the LEDs on the front panel of the fan assembly module. In addition, there is a PRODUCT ID LED/switch on the front panel of the fan assembly module (see Figure 3 ).
Figure 3 Front Panel of the Fan Assembly Module (UBR10012-FAN-PLUS)

Table 2 lists the default activation status of the PRODUCT ID LED/switch when it is shipped.
Table 2 PRODUCT ID LED/Switch Default Activation Status
Ordered Equipment
PRODUCT ID LED/Switch Status
Fan module (spare)
Activated
Fan module and Cisco uBR10012 chassis running unsupported Cisco IOS Release
Not activated
Fan module and Cisco uBR10012 chassis running supported Cisco IOS Release1
Activated
1.For information on Cisco IOS Releases that support the PRODUCT ID LED/switch feature, see the Cisco uBR10012 Router Release Notes for Cisco IOS Release 12.2(33)SCE.
If the PRODUCT ID LED/switch is illuminated (green), the Cisco IOS software identifies the fan assembly module as UBR10012-FAN-PLUS only if you are running a supporting Cisco IOS release on the chassis. If the PRODUCT ID LED/switch is illuminated (green) but a non-supporting release is running on the chassis, the software reports the default UBR10-FAN-ASSY product part number and a FAN-MISSING alarm may be randomly raised. To clear the alarm, see “Troubleshooting the Fan Assembly” section .

Tip Use a small object, such as a paper clip, to press the PRODUCT ID LED/switch inside the cavity on the front panel of the fan assembly module.

Four alarms (System OK, FAN-MISSING, PARTIAL-FAN Failure, and TOTAL-FAN Failure) are used for monitoring the fan module.
Table 3 summarizes the specifications of both the fan assembly modules.

I had the same problem.

"Bug CSCtd37319

Symptom:
The IOS first reports the fan tray status as missing, partial faliure or total failure for a brief period and later reports the status as OK.

Conditions:
This issue occurs when certain combinations of blower or the chassis have poor connector mating, causing the system software to intermittently report erroneous changes to the Fan Tray status. This condition is independent of the type of PRE."

You need to pull out and again plug tightly fan module. This can be done without powering down the cmts.
Important: all you need to do no more than 5 minutes otherwise the cmts will automatically turn off.