What it means
The A/C request input A is electrically intact, but its value does not match the system context — for example asserted while the HVAC controller reports off, toggling rapidly, or sustained while compressor pressures cannot support it. The ECM disables A/C clutch engagement until the input becomes plausible.
At a glance
- Usually lights the check-engine light
How it works
A/C request input A carries an air-conditioning demand from the HVAC controls to the engine control module. The module checks whether that request is plausible for the system; this code sets when input A conflicts with the reported HVAC state or other operating conditions.
Common causes
Most likely first.
- HVAC module sending inconsistent request
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check-engine light, if the fault triggers it
- Air conditioning may not engage
- A/C operation may be intermittent
How to diagnose it
- Record freeze-frame data and compare A/C request input A live data with the HVAC on/off command and compressor operation.
- Switch the A/C controls through their normal settings and check whether input A follows the command consistently or toggles unexpectedly.
- Inspect the A/C request A wiring and connectors for looseness, corrosion, chafing, or poor mounting.
- Check for related HVAC or A/C system codes that could explain a request inconsistent with system conditions.
- Test the request A signal and communication between the HVAC controller and engine module against the manufacturer's specification.
Common fixes
- Repair a loose, damaged, or corroded connection in the A/C request A circuit.
- Secure or repair the request sensor or switch mounting if movement is causing an unstable signal.
- Repair the wiring or communication fault between the HVAC controller and engine module.
- Replace the faulty request switch or sensor if its output is implausible after circuit checks.
Can I keep driving?
The engine can usually be driven normally, but the A/C may not engage or may operate intermittently. Avoid relying on the A/C for demisting until it works consistently.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.