Engine Compartment Cowl Removal: Owners w/Mice or Stinky AC take note...

Over the last couple of weeks I noticed that immediately after washing my 2004, I could hear water in the cowl area upon driving the car away. I decided to remove the cowl this afternoon to get rid of any accumulated debris and dirt. After removing the cowl cover I could see the two rectangular drain holes. The driver's side hole was plugged with dirt. I decided to remove the windshield wiper motor assembly and the metal cowl so that I could thoroughly clean the cowl.

If you have a problem with mice getting into the cabin air filter, then you will need to screen off the openings that become visible once the two-piece black plastic cowl cover is removed.

If you have a problem with weird smells coming from your ventilation system, a possible reason for such smells might be an accumulation of detritus that is producing the smell. (Other reasons could include a dirty cabin air filter, a plugged water drain pipe, and mold on the AC evaporator unit.)

It is good to learn how to remove the cowl if/when you decide to replace the PCV valve. After the cowl, the bolts holding the engine wiring harness to the valve cover, and the wire harness connectors to the spark igniters are removed, the PCV valve hiding under the wiring harness can be exposed and removed.

Hobbit has an excellent webpage that describes how to remove the cowl plus perform other activities, see:
Prius heat-efficiency mods

The basic steps are as follows:

• remove windshield wiper arms. Note that the windshield has a couple of dots that show where the wiper blade tips should be placed, upon reassembly
• carefully remove rubber trim at leading edge of cowl, taking care not to damage the plastic pegs that hold the trim in place
• remove two-piece black plastic cowl cover, note that each piece has one black plastic fastener at the end. Push down on the center pin, then pop up the fastener. Then remove the driver's side of the cowl cover first, followed by the passenger's side
• remove windshield wiper motor assembly
• remove relay box and sheet steel cowl pan, gently removing the plastic clamps that hold the wire harness to the cowl. Gently squeeze the clamp pegs with long-nose pliers to remove from the cowl.

Tightening torques are as follows: 57 in.-lb for the bolts holding the metal cowl to the body. 49 in.-lb for the bolts holding the windshield wiper motor assembly to the metal cowl. 15 ft.-lb for the nuts securing the windshield wiper arms.

The attached photos show the following:

• passenger side ventilation hole. Note that you can see an oblong hole behind the bulkhead that leads to the ventilation system. Ideally you would like to screen this oblong hole if you have a mouse problem, but that will not be easy since the hole is hiding behind the bulkhead. I inserted my hand into the access hole and could not feel the full extent of the oblong hole.
• windshield wiper and cowl parts that were removed
• driver's side drain hole
• passenger's side drain hole, under the VIN stamped into the bulkhead
• view of the windshield wiper motor assembly with the two-piece black plastic cowl cover removed