For most Americans, the employer-sponsored 401(k) account is truly essential to their retirement. Eighty percent of full-time workers have access to these plans, and 88 million actually participate in them.

The defined benefit pension has all but gone the way of the dodo; the defined contribution plan is the way of the future.

Dating back to the late 1970s, 401(k) plans were meant to have four big advantages for employees: tax-deferred status; the convenience of automatic pretax paycheck deductions; an employer match (in many cases) to grow the balance faster; and, finally, at least for big plans with lots of assets, lower management fees.

On the last point, too often the benefit exists in theory rather than in practice. Large companies are supposed to be able to negotiate better rates on investment management fees than retail investors can do alone, saving individuals money.

Today there is $4.89 trillion invested in these plans. Jerry Schlichter, managing partner of a law firm in St. Louis, says that kind of cash is tempting some companies to steal from the cookie jar. In other cases, they're just lax about keeping away the mice.

Last year, Schlichter's firm won a $35 million settlement on behalf of participants in the 401(k) of Cigna, the health insurer. He represented employees in a suit claiming the plan, which was heavily invested in Cigna financial products, had charged them excessive fees.

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Here are red flags to see if your job's 401(k) is a lemon. It might inform your decision to stay in your job -- and these are good questions to ask if you're looking for a new one.

What options are there? The lack of low-cost index funds and the presence of lots of funds with the name of your company or its subsidiaries are bad signs.

What are the expense ratios? "We were shocked that Fortune 500 companies with billion-dollar 401(k) plans had retail mutual funds in them and employees paying retail fees -- 1.25 percent," as opposed to 0.5 percent for a low-cost index fund, says Schlichter. That may not seem like much. However, it adds up. A 1 percent difference in fees over a work life of 30 years for an employee can make a 28 percent difference in returns.

How can I find out more? There are lots of rules about proper disclosure for 401(k) plan sponsors. Yet, Schlichter says, companies often adhere to the letter of the law by burying pertinent information in the fine print.

If you can't figure out the information you want to know, just ask a human resources person. A corporation working in good faith will want to be alerted to the fact that its plan management needs an upgrade.