I have a chevy colorado. only the high spped fan works. there are no indicated fuses for the fan system what can the problem be

There isn't one. The function is done by the Body Control Module (BCM) along with lots of other functions.

Where is the turn signal relay on a 2006 Chevy Colorado?
The turn signal is controlled by the BCM (Body Control Module) that is located at the passenger side kick panel.
May 21, 2014

2006 Colorado turn signal relay? where is it - 355 Nation

Known issue

BODY CONTROL MODULE PROBLEMS - Colorado Fans

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ck switch for power in and out if power out ck resistor

Check the blower motor resistor in the front of the passenger side floorboard

Start by checking GM Technical Service Bulletins

Lots of issues on most Colorado's

You have a relay there are 2 speeds low speed and high speed this is controled by a cooling fan module if you changed fan and it does not work then you will need to check the fan module, first the relay its in the engine fuse junction box High speed is marked on the relay C1056 and low marked C1058, here is what you can do go to the high spped relay open thhe cover and expose the relay with key on collapse the relay does the fan come on? if it doesnt replace the fan module if it does you will still have to replace the fan module here is the location is at the radiator on the front (may be under shroud)

Check with Chevy on a Technical Service Bulletin on that issue

code 420= Catalyst system efficiency below threshold(bank 1) code 496=Evaporative emission system-high purge flow. Hope this helps if you need more help get back to me Thanks Ray

The resistor needs to be replaced, common on the Colorado's
http://coloradofans.com/forums/viewtopic.php?f=8&t=48293&p=1038821&hilit=resistor#p1038821
 

Could be a fuse, but try it all the way on high first. If it works on high only, it's most likely the resistor in the fan control. Hapened to mine a couple of times and Chevy charged me about $150 to fix it.

You need a resistor pack, which is likely located in the air box, near the blower motor.