Where does fan speed sensor go in 2004 trailblazer

the fan resistor is bad. Most fan resistors have a different size wire for each fan speed which controls the fan speeds, the small wire is low speed ETC, This site will show you how to replace fan resister--- https://www.youtube.com/watch?v=Be61A67ltP4 - When utube comes up, Please click on 7th link down on right side of page. Good-Day!

See attached picture for location of temp. sensor, but that code has nothing to do with temp sensor. The speed of the fan does not agree with the commanded speed, you may have another bad fan clutch.

Replace sensor

Assuming that you're talking about the front wheel speed sensors...
Your best bet is to replace both from wheel hub/bearing assemblies.

They'll cost about $100-$150 each.
When the wheel speed sensors are setting ABS codes it usually means that the bearings are bad.
When you replace the whole hub assembly, a new sensor is already installed in that hub. If it just the sensor (unlikely that just the front sensors alone are going bad) the sensor itself is usually 3/4 of the price of a new hub anyway.

I’m happy to help further over the phone at https://www.6ya.com/expert/jason_00b31cc8f593773a

Did you replace the thermostat and bleed all the air out the system also? The fan clutch needs to be checked to make sure the fan is fully engaged or the engine will overheat.

This an indication of the fan clutch gone bad or a problem with the wiring harness. The computer controls the speed of the fan by engaging the clutch, without the speed sensor signal being present, the computer can't control the speed so the fan will only spin slowly. If you are driving in very hot weather or heavy traffic, you may encounter an overheating condition.

A couple of things come to mind. Double check the wiring at the fan clutch, check the whole harness, there is a known problem wth chaffing there. Is it a Dorman brand fan clutch? These have been known to be bad out of the box. The other thing that could be wrong is the actual speed sensor on the new fan clutch. Hope some of this helps.

CODE PO526 - FAN SPEED SENSOR. POSSIBLE CAUSE WIRING POOR CONNECTION BAD SPEED SENSOR.

p0526-- fan speed sensor curcuit, p0495 is fan speed high, p0410 is secondary air injection system malfunction.

Hi.
The cooling fan speed sensor is built in inside the fan clutch.
If you have a code p1481 or similar , pointing at the cooling fan speed sensor, often you have to fix or replace the wiring , rather that the sensor.
Check that wiring has continuity, the wire to sensor must have +5V. Here an interesting website on trailblazer fan system.
Regards.