code 51

[Lincolnmania]

i'm working on a fellow box owners grand marquis
symptoms are it surges, idles rough and lacks power and gets poor fuel economy.........i scanned for codes, came up with a code 51 (ECT sensor signal is greater than the Self-Test maximum of 4.6 volts.) the sensor and wiring seem to check out ok checking voltage and ohm readings of the sensor (sensor appears to be new) i checked connections at the coolant temp sensor and is good.........anybody have any clue what would cause the problem?

[Lincolnmania]

oh i forgot to add that the cap and rotor, wires, spark plugs, o2 sensors tps are also new, so i've eliminated them.......really thinking this code 51 is the problem, runs too rich all the time

[mrltd]

there has to be a short somewhere in the harness, giving the Vref to the pin on the ECM.

[88grandmarq]

the correct definition of code 51 is ECT sensor fault or circuit open. this code only occurs during engine running or continuous test modes.

so you either have a faulty sensor, a wiring problem or a faulty ECM.
First thing you need to do is clear the trouble codes, pull the negative battery cable and step on the brake pedal. Drive the car and re-test for codes.
You may try swapping the sensor with a known good sensor. Also make sure the coolant is full and clean. Do NOT use any pipe tape to seal the sensor, use light skimming of silicone or liquid thread sealer.
one of the quick tests says to disconnect connector and use a jumper wire to connect the 2 wires together in the connector. run the motor and re-test for codes, If code 61 shows up the wiring is good and the sensor is faulty. if code 61 does not generate you have faulty wiring or ECM.
you may try swapping in a known good ECM and see what happens.
if you suspect a wiring problem, inspect the connection at the large white and black engine wiring harness connectors. It's the light green and yellow wires for the ECT sensor.

[gadget73]

This is a repost from an IM, but its relavent.

gadget73: looks like the lg/y wire goes from pin 7 on the ECM to the ECT, and the bk/w wire is a common wire from the ECT, and it also ties in with the bk/w on the EGR, TPS, IAT, MAP, test connector, and pin 46 on the ECM.

[Lincolnmania]

i swapped in another lopo ecm, the code 51 is gone for now......gotta swap the replacement ecm under the dash and take it out for a spin