What it means
The voltage B feedback of the electric A/C compressor motor is below the expected window. Phase wire shorted to ground or driver fault.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The control system monitors voltage feedback B for the electric A/C compressor motor. P2D42 sets when that signal is below its expected window, pointing toward a phase B short to ground or a low-side output-driver fault rather than an overvoltage condition.
Common causes
Most likely first.
- Phase B wire shorted to ground
- Output driver low-side fault
Symptoms
- A/C warning or check-engine light
- Reduced or no cabin cooling
- A/C may switch off
How to diagnose it
- Record freeze-frame data and check voltage B feedback and compressor commands to confirm the low reading occurs when the compressor is requested.
- With the vehicle powered down as specified by the manufacturer, inspect the compressor phase B wiring and connectors for damage, moisture, or contact with ground.
- Check the phase B circuit for a short to ground using the vehicle wiring diagram and the manufacturer's safe test procedure.
- Inspect the compressor control module connector and wiring for damaged terminals that could affect its low-side driver.
- If the harness is not shorted, test the output driver and compressor circuit against the manufacturer's specification.
Common fixes
- Repair chafed phase B wiring that is shorted to ground.
- Clean, secure, or replace damaged compressor circuit terminals.
- Repair the affected harness section or connector.
- Replace a confirmed faulty compressor output driver or control module.
Can I keep driving?
Driving is generally possible if the vehicle has no other warnings, but the A/C may shut off and cabin cooling may be lost. Avoid relying on A/C for defogging if visibility could be affected, and stop if a hybrid-system warning or power reduction appears.
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.