(FORTUNE Magazine) – Like the sound of a juicy 5% dividend yield? If so, you may be tempted by shares of General Motors (GM, $40). Why not buy stock in this $196 billion titan of American commerce? After all, it's trading at a fire-sale price/earnings ratio of 5.9--less than half that of the average S&P 500 stock--and only 80% of its book value. Isn't it worth it solely for the dividend?

Truth is, these are shares you should leave on the lot. And they're the perfect illustration of why a seemingly alluring low P/E and high-dividend yield may signal danger for investors rather than opportunity.

GM's struggles are well known. The company's earnings came in well below forecasts this quarter, and as a UBS release blandly put it, "Weakness Expected to Continue." The litany is familiar: eroding U.S. market share, ever thinner margins thanks to heavy discounting, and troubled European operations. Throw in the looming threat of health-care and pension obligations, and even the healthy returns of the GMAC financing division aren't likely to generate growth.

More important, while GM may be eternal, its dividend hasn't been. Historically GM has slashed its payout in hard times. "Every recession," says Morgan Stanley's Stephen Girsky, "they cut the dividend." Be careful, adds fellow analyst John Casesa of Merrill Lynch: "Earnings are extremely volatile in this business." -- Oliver Ryan