2001 mercury Grand Marquis temp gauge reads cold all the time, jump switch goes all the way up . put in new switch still have same problem

Bad ECM, bad wire from the ECM to the instrument panel, and a bad motor for the temp gauge.

Run self test on heater control head. With the key press off and floor buttons at the same time for 2seconds then release and press auto button for a second.this will put system into self test.if no code all the blend door actuators are ok and I would think vacuum leak from main vacuum, black line going through fire

Check sending unit, Ford/Mercury put out a TSB, technical service bulletin : Article No. 95-13-2 07/03/95, on erratic temp sender units.
You troubleshoot as follows :

1. Turn ignition switch to On or ACC position.
2. Connect a 10 ohm resistor between gauge lead and ground. The centerline of pointer should fall within the band around the H mark.
3. Connect a 73 ohm resistor between gauge lead and ground. The centerline of pointer should fall within the band around the C mark.
4. If gauge tests within calibration, replace sender.
5. If gauge is out of calibration, replace gauge.

If you changed the #5 Coil then the code was wrong

You get lots of wrong codes on a ford, as a bad coil
spikes the pcm when grounding out to fire the coils
secondary side

Try putting the old coil back & walking the new one to
another cylinder,may take many days & many miles of
driving to get it fix,but better than a shop guessing, because
they hate fords

Check under the dash at your Brake pedal interlock switch. It is timed with the gearshift Interlock and Ignition switch. This switch usually gets hit by feet and dislodged or broken. When you shift out of Park, the switch is toggling to a broken piece and shorting out.

The brake interlock switch is at the top half of the pedal lever. The other part of the Interlock uses a rod or cable in the steering column Ignition switch and mates with the shifting mechanism.

Im assumint that you have any fault code stored there, what code was set? Where the Temp gauge and PCM now share a temp sensor, an early guess would be a wiring issue...



Keep us updated.

need to check to see if radiator is circulation the water . hose good make sure their no soft an sucking shut especaily the bottom hose . you can get a temp gauge take radiator cap off ,let warm up til thermostat opens put gauge in radiator see what temp. is . (wife got meat or candy temp gauge this will work) last it could be heater core bad.

it doesent mean the weather it works the same if the engine hasent been rann for awhile its not at operating temp try running it till it reaches normal temp if it does not stall its your cold oxigen sensor

Have you checked the fuse under the dash. You can run power directly from the battery as you did to test the blower just make sure you use a high amp rated switch and make sure you install an inline fuse rated no more than ten amps if you use say 14 guage wire. Let me know how it goes good luck.

it is located on top of the intake manifold right behind the thermostat housing where the upper radiator hose goes to engine