2000 Mercury Grand Marquis:
Check Engine Light, Code P0456 and more

Question:

I own a 2000 Mercury Grand Marquis with 41,000 miles. On Monday the Check Engine Light went on. The code was PO456. The mechanic managed to turn the light off and told me to drive the car for 60 miles for testing purposes.

On Thursday the Check Engine light went on again. The codes were PO174, 1151, 1131, 171. The mechanic was reluctant to fix it. He suggested bringing the car to the dealer. Can you tell me what these codes mean?

Answer:

The initial trouble code stored in the system's memory, PO456, indicates a very small leak of fuel vapors from the evaporative emissions control system.

The bunch of codes which came up following your test drive refer to the system's unsuccessful attempts at compensating for an excessively rich condition (too much fuel) by reducing the amount of fuel delivered to the engine by the fuel injectors.

The first code and the second group of codes may or may not be related, but you want to deal with the most recent first. And there's a good sized list of possible causes, beginning with a problem in the fuel delivery system (high or low fuel pressure, leaking injectors, etc) and including the vapor recovery system which prompted the initial trouble code.

If the technician on the job suggested a Mercury dealership service department for further diagnosis, by all means take his advice.

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