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

[GLStang]

Recently purchased a 2016 GT with 52K on it. Was running good. My son and I put a JLT CAI and custom tune. After about 15 minutes after you drive it the car thinks it’s over heating. The coolant light comes on and temp gauge goes to C and the car thinks it’s overheating. I check the gauge reading and head temp is normal. I’m getting codes P1285 and P1289. I thought it was the cylinder head temp sensor but the first mechanic said that it checked out fine but they found code U0401.

The problems started once we flashed custom tune. BAMA/SCT has done a number of things but no fix. I now have the stock tune and stock filter on and same issue slightly worse actually.

Any thoughts or ideas would be greatly appreciated on how to fix this.

 

[Noobz347]

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).

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.