Question about 1999 Mercury Grand Marquis

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My 99 Grand Marquis was a gift from my grandmother. With 104k mi. I am confused by apparent symptoms that all seem to be tied to 1 main cause. Possibly a control box or computer is causing AC, power steering, braking, transmission?, to become uncalibrated. I removed the neg battery cable over night and the next day it ran almost perfect until i had to turn it off. By the 3rd or 4th time it was back to terrible. Can you help please

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The best thing for you to do is go to Autozone, Oreillys, or another parts store where they give FREE scans of the onboard computer. The onboard computer should have some information in it.

Some of your problems can be related but more information would be needed in your description.

First, the Power steering is not connected to the Brakes, Transmission, and only shares the Serpentine belt with the A/C. The Power steering is a hydraulic system. Check the fluid level for the Power steering as well as the Brake fluid and the Antifreeze levels. Exactly what is the car doing when you steer it?

Second, Braking- Does it stop? Is it making any noise and what does the noise sound like? Is there a Warning light on in the dash?

Third, the Transmission. Check the Trans fluid level with the engine warm. Now the Trans does have Electric controls which can be computer controlled and they are linked to the Engine controls. How is it shifting?

Fourth, the A/C. Worry about the first 3 things unless you have no heat or blower control. The AC is a Luxury and it won't stop you from driving the car. It is easier to diagnose once you describe the symptoms and has little effect on the Engine controls.

This model is a very good car. Gas mileage was good to excellent, they are comfortable and dependable. Once you fix this car it will stay fixed. They easily run 200,000 to 250,000 miles.
Parts are available at Salvage yards and most every part is available in lower cost aftermarket parts. Every shop has worked on them, they are used for Taxis and Police cars.

Go to get the scan AS IS. Do not disconnect the Battery. Let it run its own crummy way so when you scan it the problems can be caught. If the car has set for a time, the gas may be flat.

Posted on Nov 07, 2010


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