Pulling a P0118 ECT code, what does this mean?

P0118 -ECT Circuit High Input

Since you asked specifically about the P0118 DTC, let's start there. The DTC indicates that the sensor's voltage return to the PCM is TOO HIGH.

This usual is cause the a hard FAULT in the circuit. Suggest start by inspecting the wiring harnes to/from the coolant sensor. Look for loose/chaffed/burnt wires. Look at the connector itself. Is it plugged in all the way?

It is also possible that the sensor itself is bad. Also note that the DTC refers to the cylinder head sensor but the Mustang does not have a CHT. On applications that do not have a CHT, the DTC means coolant sensor.

OBTW, on the 4.6 SOHC the coolant sensor is located on the right hand side of the intake manifold crossover near the alternator.

Does your scanner also monitor ODB2 data? If so, use it to monitor the engine coolant temperature. Is it reasonable?

The PCM uses the engine coolant sensor to make various decisions regarding engine management. Things like O2 open/closed loop, engine fan settings and others depend on an accurate coolant temperature. So it may or may not be causing your other problems. IMO, it can't be helping the situation.

However, if you have been disconnecting the coolant sensor doing other work, this could account for the DTC.

Regarding the other DTC codes. Where do you stand regarding vacuum leaks and exhaust leaks?

Also check your fuses. Esp fuse F2.8 in the CJB.

>>From Ford service CD
P0118 - Engine Coolant Temperature (ECT) Circuit High Input

Indicates the sensor signal is greater than Self-Test maximum. The ECT sensor maximum is 4.6 volts or -50°C (-58°F). Note on some vehicles that are not equipped with an ECT sensor, CHT can be used and can set this DTC.

Open circuit in harness
Sensor signal short to power
Damaged PCM
Improper harness connection
Damaged sensor

ECT V PID reading greater than 4.6 volts with key ON and engine OFF or during any engine operating mode indicates a hard fault.

IronD01GTvert said:

So my SES Light came on and I'm showing a few codes. My scanner showed these 3: P0118, P1131 and P0172 P. I know the last 2 have to do with one of my cats, since it is effed.

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This is probably incorrect.

P1131 points to bank 1, sensor 1 not switching and showing lean. Since this is before the cats, it's not related to them. The sensor is likely bad or the wiring is suspect.

P0172, interestingly, contradicts P1131 by indicating a rich condition for that bank. Both codes are related to the front (pre-cat) O2 sensor or its wiring.

I have a feeling If I get the cat replaced these will go away...

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You would be seeing catalyst efficiency codes, not fuel mix/sensor codes. The problem is not the cats.

but what is the P0118? I know it has to do with "P0118 - ENGINE COOLANT TEMPERATURE CIRCUIT HIGH INPUT" but what does that mean?

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It likely means either the engine coolant temp sensor is unplugged, defective (open circuit) or the wiring to it is bad.

It's located in the intake manifold at the coolant crossover near the front, passenger side I believe.

IronD01GTvert said:

As far as the other codes go. Which sides of the car do these numbers refer to? I believe I have heard that bank 1 refers to whichever side cylinder #1 is located on and i believe that is the passenger side on the 01 GT 4.6L.

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This is correct. B1 is the passenger side.