help with hardware test error code

4MOT/4/40000002 :CPU-xxx
CPU fan/blower, located next to left speaker (logic board has to be removed to replace CPU blower)
Verify that the CPUblower/ fan cable is securely connected to the left side of the logic board and that there are no obstructions that would prevent the blower/fan from rotating. Replace fan if the error continues.
Normal fan operation, except the CPU blower
Note: Make sure black mylar tape along the bottom of LCD panel is not obstructing fan blades, if so, cut tape and re-stick to LCD.

 

iMacs generate fan errors when rpm is 10% or more off the target rpm.

I would proceed as follows:

1/ SMC reset (unplug power cord for a few minutes when imac is shut down), and see if the problem is still there.

2/ Open it up carefully (following step-by-step instructions on youtube, ...), use a compressed air can to get rid of all the dust and check for anything else that could be straining the CPU fan (like the mentioned tape).

3/ If the problem persists, buy a new CPU fan e.g. on ebay

If you don't feel comfortable doing this, seek help

Good luck!