Faulty A/C request switch or climate control head unit sending an incorrect signal.; Damaged or corroded wiring in the A/C request circuit, including open or short circuits.; Poor electrical connection at the PCM or climate control module connectors.; Failed A/C pressure sensor or transducer providing implausible data that affects request logic.; PCM software issue or internal fault in the A/C request input circuit.; Aftermarket accessories or remote start systems improperly tied into the A/C request wire.

DTC codes / P25xx · Vehicle speed, idle control and auxiliary inputs / P255F

P255FA/C Request A Circuit Range/Performance

Q: What does code P255F mean?

A/C Request A Circuit Range/Performance. P255F indicates that the air conditioning (A/C) request signal from the climate control module is outside the expected range or performance criteria, so the powertrain control module (PCM) cannot reliably determine when A/C is being requested. The PCM monitors the request circuit and sets this code when the signal voltage or timing does not match what the module expects under the current operating conditions.

P255F indicates that the air conditioning (A/C) request signal from the climate control module is outside the expected range or performance criteria, so the powertrain control module (PCM) cannot reliably determine when A/C is being requested. The PCM monitors the request circuit and sets this code when the signal voltage or timing does not match what the module expects under the current operating conditions.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

The A/C may not engage at all, or it may blow warm air even when the climate control is set to cold.
The A/C compressor clutch may cycle erratically or fail to engage when the button is pressed.
The check engine light (malfunction indicator lamp) is illuminated, often with no other driveability complaints.
The climate control panel may show normal settings but the system does not respond to request changes.
In some vehicles, the A/C may work intermittently depending on temperature or electrical load.
Often no symptoms besides the warning light, especially if the fault is in the signal circuit rather than the compressor itself.

Common causes, most likely first

Faulty A/C request switch or climate control head unit sending an incorrect signal.
Damaged or corroded wiring in the A/C request circuit, including open or short circuits.
Poor electrical connection at the PCM or climate control module connectors.
Failed A/C pressure sensor or transducer providing implausible data that affects request logic.
PCM software issue or internal fault in the A/C request input circuit.
Aftermarket accessories or remote start systems improperly tied into the A/C request wire.

How to diagnose and fix it

Verify the code with a scan tool and check for any related codes in the climate control or body control modules.
Inspect the A/C request circuit wiring and connectors for damage, corrosion, or loose pins.
Test the A/C request switch or climate control panel output signal with a multimeter or oscilloscope.
Check the A/C pressure sensor readings against actual system pressures to rule out sensor errors.
Perform a wiggle test on the harness while monitoring the A/C request status on the scan tool.
If the signal is correct at the PCM but the code persists, follow the manufacturer's diagnostic flow for PCM input testing.
Repair or replace the faulty component (switch, sensor, wiring, or module) and clear the code to confirm the fix.

When the A/C request signal looks fine

A common oversight is assuming the A/C request switch is bad when the real problem is a chafed wire behind the dashboard that only shorts when the engine moves under load.
The PCM may set P255F even when the A/C system itself is fully functional, because the code monitors the request signal's electrical characteristics rather than the compressor's operation.
Aftermarket remote start or alarm systems spliced into the A/C request wire often introduce voltage spikes or ground offsets that trigger this code intermittently.
On some vehicles, a weak battery or charging system issue can cause the climate control module to send erratic request signals, setting P255F without any hard fault in the A/C circuit.
Technicians sometimes replace the climate control head unit unnecessarily when a simple terminal tension adjustment at the PCM connector resolves the intermittent signal.

Can I keep driving with P255F?

The vehicle remains safe to drive because this code affects only the A/C request signal and does not impair engine operation or safety systems. You can continue driving, but avoid using the A/C until the fault is repaired to prevent unnecessary compressor cycling and potential further electrical strain.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.