2004 GMC Envoy with a P0526 sensor problem

P0526
In order to maintain proper powertrain cooling requirements, and to reduce the cooling fan noise as it is in use, the PCM uses a signal from the cooling fan to assess its speed. If the speed of the fan is higher or lower than the manufacturer’s specifications, the PCM will store the code P0526.

What causes the P0526 code?
In most cases, the P0526 code is caused by a faulty cooling fan motor. However, this code may also be stored due to:

Faulty cooling fan relay
Corroded or loose electrical components
Faulty engine coolant temperature sensor
Shorted or open electrical wiring, which may cause a blown fuse
Faulty cooling fan

this shows info and repair for the p0526 its basically the fan clutch but on an envoy and trailblazers their electronic- prices vary but if this code popped up after changing plugs check the connections and harness for disconnect or damage ---recheck the plugs that the coil s are good and wires are on tight https://www.youtube.com/watch?v=UxwUvTiqtTA

Neither work? replace the turn signal switch.

p0526 Google Search

Ckeck your cranck shaft sensor and if all fuses are good and see if you have fuel too

The fuel level sensor is in the gas tank, and if it needs to be replaced, the tank must be removed from the truck.
Does your gas gauge work correctly? If not, there could be a bad connection at the tank/sensor or the sensor itself is defective.

is your "service engine soon" indicator lit?If so have the computer scanned for error codes and post it on fixya. If not, many issues can cause this (cam sensor, crank sensor malf, faulty coil, fouled spark plugs, vacuum leaks)

Service Engine Soon (SES) or Check Engine Light On, DTC P0480, P0526/P1481/P1484 Set (Replace Engine Cooling Fan Wiring Harness) #05-06-02-012B - (10/19/2006)

Models:2004-2006 Buick Rainier
2002-2006 Chevrolet TrailBlazer, TrailBlazer EXT
2002-2006 GMC Envoy, Envoy XL, 

Some customers may comment that the Service Engine Soon (SES) or Check Engine light is illuminated. This condition may be intermittent and upon investigation, the technician may find either DTC P0480, P0526, P1481 or P1484 set.

This condition may be caused by the cooling fan harness chaffing against the plastic guide it routes through. This contact may damage the insulation of the wires enclosed in that harness.

Replace the wire harness: 
Part Number 89024920 Description Harness Assembly, Engine Cooling Fan Wiring

Good luck and keep me posed. 

there is a fuse box under rear seat and also under the hood they should have cover over both with labels for what is what.

The sensor is located on the drivers side engine block...although you can see if from looking from the top of the engine, you would have to get under the vehicle and look up to replace it. Be aware that it takes a special tool to unscrew the old one and screw in the replacement.