Mercury Grand Marquis owners have reported 1 problem related to speed sensor (under the vehicle speed control category). The most recently reported issues are listed below. Also please check out the statistics and reliability analysis of Mercury Grand Marquis based on all problems reported for the Grand Marquis.
The passengers side seat beat comes undone at times and the speed sensor works intermittently and it leaks gas from around the fuel pump.
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all problems of the 1999 Mercury Grand Marquis
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