Mercury Grand Marquis P0601: Meaning, Causes + Diagnosis

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P0601 Mercury Grand Marquis

P0601 is a somewhat rare OBD2 trouble code.  It’s a generic code (it has the same meaning for the Mercury Grand Marquis as it would any other vehicle).

While it indicates that the PCM’s memory failed a memory check, P0601 is commonly seen when people use OBD2 port plugin accessories on their vehicle.  These accessories are used to turn off cylinder deactivation technology, auto engine start/stop, and performance plugins.  If this is the case with your Grand Marquis, unplugging it may clear the code.

P0601 Definition: Internal Control Module – Memory Checksum Error

P0601 Definition: Mercury Grand Marquis

Your Mercury Grand Marquis’s PCM (powertrain control module) has memory and a processor like any other computer.  The PCM’s processor performs a “checksum test” to verify the integrity of its onboard memory. 

If the PCM fails this self-diagnostic test, P0601 will be stored, and the check engine light will come on.

P0601 Symptoms:  Mercury Grand Marquis

The symptoms associated with P0601 are wide-ranging if there are any at all.  It’s likely that your Grand Marquis will run and drive when normally when this code is present.  Here are the most common symptoms of P0601

  • Check engine light– Other codes are likely to be present with P0601.
  • No start– The engine will have difficulty starting or won’t start at all.
  • Engine performance issues– The PCM controls the engine.  So the engine may stall or act erratically.

Mercury Grand Marquis P0601 Causes and Diagnosis

P0601 Diagnosis

Here are the most common causes of P0601, as well as a proper order of diagnostic operations:

1. Reflashed PCM or OBD2 Dongle

If your computer was reflashed with a tune that Mercury did not approve, that can cause P0601.  You’ll need to have the PCM reflashed.

Those little dongles that plug into the OBD2 port that modify the way the your Grand Marquis runs or drives, they are notorious for causing P0601.  If you have one of these, pull it and reset the code.  If it doesn’t come back, you shouldn’t use the dongle anymore.

2. Bad PCM

Most of the time, with P0601, the only solution is to have the PCM replaced or reflashed, which means taking your Grand Marquis to the dealer.

Conclusion

There’s not a lot you can do to fix P0601 in the Mercury Grand Marquis at home.  The good news is that the PCM may be subject to the eight year 80,000 mile federal emissions warranty.  Here’s a link if you want to read more about that.