2016 GT, Cold Air/Tune Trouble (overheating) . Advice/Help Please!

You’ve already done a lot of the right things, so here’s how I’d look at it.


P1285 – Cylinder Head Overtemperature Protection Active
P1289 – Cylinder Head Temperature (CHT) Sensor Circuit High Input (Bank 1)
U0401 – Invalid data received from PCM/ECM


What stands out is that the problem started right after the CAI + custom tune.

Even after swapping back to the stock airbox and stock tune, the issue got a little worse, which suggests either a wiring/sensor fault or possibly a corrupt PCM calibration.



Things to check:


Coolant / CHT sensor wiring
The CHT sensor is not the same as the ECT. On the 2016 Coyote, the CHT sensor is threaded into the driver-side cylinder head near cylinder #2. The harness runs right by the intake — it’s easy to pinch, stretch, or leave the connector loose during a CAI install. Inspect the connector and wires closely for bent pins, corrosion, or chafing. A broken or open wire can cause the PCM to see 0 V or 5 V and think the engine is overheating.


Grounds
Make sure the PCM grounds and engine grounds are clean and tight. A floating ground can throw off the reference voltage and cause false over-temp readings.


CHT sensor itself
Even if it “tested good” once, these sensors can fail intermittently. They’re inexpensive (Motorcraft CX-2231 is the OEM part). If the wiring looks fine, replace the sensor as cheap insurance.


Tune / PCM
That U0401 code points to corrupted or mismatched PCM data. If the problem continues after verifying the CHT sensor/wiring, have the PCM reflashed back to the latest stock calibration with Ford IDS/FDRS at the dealer. After you’re confident the stock file is solid, reload your custom tune.



Likely causes in order


-CHT sensor wiring/connector damaged or loose during CAI install.

-Faulty CHT sensor (even if it ohms OK).

-Corrupt or mismatched PCM tune file.

-PCM internal fault (rare).

Pin Out Info said:

CHT Sensor PCM Pinout (2015–2017 5.0L Coyote, PCM Connector C175B)


Pin 39 – CHT Signal (usually Violet/Gray wire)
Pin 91 – CHT Signal Return / Ground (Gray/Red wire)


Expected voltage checks:
• Key ON, engine cold (~70°F): about 3.5 V
• Warm engine (~176°F): about 0.8 V
• At 212°F: about 0.5 V


If you see 0 V or 5 V flatline, suspect an open/short in wiring or a failed PCM input.

Click to expand...