Time to read the manual. The manual said that either too much suds or the drain pump was having a problem. I went to the Internet to try to find more information. Jackpot! I found a post of the description and the fix for the error code.
It was obvious that excessive suds was not my problem.
You will need a towel, a flashlight and a 4d nail / brad (or some other metallic pointed thing). You may or may not need some silicone grease to lube the sump cap. (I did not need any.)
If you have water in the drum of the machine, you will need a wet/dry vacuum cleaner with crevice end and more towels and maybe ear plugs if your vacuum is as loud as mine.
Note: Wet/dry vacuum cleaners use 2 inch and/or 1 and 1/2 inch hoses. The smaller hoses and accessories are easier to maneuver inside the washer.
Step 1: Gaining Access
The access for the drain pump is behind the circular access panel on the bottom right front of the machine. This panel twists off. There are three ears on the panel that fit into three cutouts on the machine front. After the ears are in the cutout, the panel is twisted counterclockwise to lock ears behind metal.
If the panel were a clock face, there is a small hole in it at about the 5. Insert a nail in the hole to gain some leverage. Gently press on the panel with your other hand while you rotate the panel clockwise to move the hole to the 6 o'clock position.
Update - 10/2011: Be careful when you get the cover off. The edges of the hole may be unfinished and sharp. You can tape over the edge while you are working or wear gloves. The more adventurous can grind or file the rough edges.
Step 2: Removing the Sump Cover
Be careful when you reach into the sump area because the edges of the hole may be unfinished and sharp. You can take a file/grinder to the edge, or duct tape the edge, or wear gloves.
Stuff as much of a towel as you can under the cover and under the machine to catch some of the water. The error occurred mid wash for me so there were gallons of water in the drum. One towel was not going to be enough.
The cover is screwed in only hand tight. It might have been the hand of gorilla but you should not need tools. Righty-tighty lefty loosey.
If there is water in the drum, DO NOT REMOVE THE COVER . Only break the seal by turning one quarter turn.
I do not know if the sump is ever empty. I suspect it is empty at the end of the cycle but you would not get the e.04 error at the end of the cycle.
Update 6/2012 - I opened the sump in response to an o-ring question posted here and found that the sump is not empty at the end of the cycle. It contains about 1 quart/litre of water. So you need very very thirsty towels or the vac.
Step 3: Sucking Out the Water
Assemble the hose and crevice tool onto your wet/dry vacuum. Turn on the vac. There is a protrusion - a lip - at the bottom of the sump face. Water will puddle there as you loosen the cover. Place the crevice tool at the lip on the sump. Slowly loosen the cover until water comes out as fast as the vac can suck it up. Turn off the vac when water flow has stopped. My washer had about 5 gallons (20 litres) in it. (NOTE: That's about 40 pounds (80 kilograms) of weight. You may need to get help to lift the vac when emptying it. If no one is around to help, just don't empty the washer all at once.)
Step 4: Remove the Sump Cover
You can see a "black-white-black" sandwich at the end. It is the gasket - impeller base- cover. See the other pictures to see how the gasket fits in the sump cover. Carefully pull the gasket out of its groove to clean it and the groove.
Step 5: Removing the Junk
Step 6: Final Clean Up and Reassembly.
The impeller housing was kind of grundgey so I cleaned it. I found I had to stick a towel into the sump while I cleaned because water was still puddling at the bottom.
Most of the dirt came off with direct scrub with an old toothbrush. But there was some resistant scale that responded to the pointed end of a nail.
Update 8/2016 White vinegar is often used on stubborn deposits, Sometimes a spray works, sometimes you need a soaking. There are specific mineral-deposit-cleaning products if your water is particularly mineral laden.
The impeller housing is marked to indicate which way goes down. Align the housing and screw the cover back in. I did not see any kind of thread lube / sealant, so I did not apply any. Usually sealants are not used on plastic. However, sometimes there is silicone grease on o-rings. If your model had grease, reapply a little bit if you wiped it off during cleaning or during removal.
Insert the cover and screw it down hand tight. Run the short cycle to check for leaks.
Reattach the access panel.
Smile because you just saved at least $50 on a service call. Now pay it forward and bless someone.