P2D42

Code

Generic P — Powertrain

A/C Compressor Motor Voltage B Low

Brand: Generic

Type: P — Powertrain

Views: UK: 27 EN: 45 RU: 32

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Causes

Low vehicle battery or system supply voltage
Blown fuse or open circuit protection device in compressor B feed
Faulty A/C compressor motor (rotor/stator issues) or motor driver/module
Open, short to ground, or high-resistance wiring/connector in compressor motor B circuit
Bad or corroded ground connection for compressor motor or control module
Faulty relay or contactor supplying the compressor B circuit

Symptoms

Reduced or no A/C cooling when compressor is commanded
Compressor does not engage or make expected noise when requested
Diagnostic trouble light or A/C system warning on dash
Intermittent A/C operation (works sometimes)
Unusual noises from compressor if mechanical problem is present

What to check

Read freeze-frame and live data with a scan tool; confirm P2D42 is active and note conditions when set
Verify battery resting and charging voltage (nominal ~12.6 V at rest, ~13.5–14.8 V while running) or OEM-specified supply for e-compressors
Inspect fuses, circuit breakers, contactors and relays for the compressor circuits (replace if blown or suspect)
Visually inspect wiring and connectors for damage, corrosion, loose pins, or water intrusion at compressor and control module
Measure voltage at compressor motor B power terminal with A/C requested and engine/runs as required; compare to expected voltage
Check ground connection(s) for continuity and low resistance

Signal parameters

Expected supply voltage at compressor B terminal: approximately battery/charging system voltage (vehicle-dependent); significant drop or 0 V indicates feed fault
PWM control signal: duty cycle 0–100% when commanded by control module (frequency and behavior are OEM-specific)
Compressor motor current: nominal running current per OEM spec; abnormally high current may indicate mechanical seizure or internal short
Resistance of motor B winding (ohms): must match OEM specification; open or shorted winding indicates motor failure
Diagnostic DTC set conditions: low-voltage threshold crossed while compressor request active (check module-specific thresholds in service literature)

Diagnostic algorithm

Verify complaint and scan for P2D42. Record freeze-frame data and any related codes.
Check battery state of charge and charging system. Recharge or repair battery/charging faults before proceeding.
Visually inspect fuses, relays/contactors and wiring for the compressor B feed. Replace blown protection devices and reseat connectors.
With ignition ON and A/C request active (use scan tool to command if available), measure voltage at the compressor motor B power terminal and ground. Note voltage under no-load and while commanded.
If no or low voltage at compressor connector, trace feed back to relay/fuse and control module. Check relay operation and supply feed continuity. Repair wiring/connector faults.
Check ground(s) associated with the compressor and control module for tightness and low resistance to chassis/negative battery terminal. Clean/tighten as required.
If supply and ground are good at the connector but issue persists, test motor winding resistance and perform a current draw test while commanding compressor. High current suggests mechanical/motor fault; low/no current suggests open circuit in motor or driver.
Inspect/diagnose any dedicated motor driver/inverter module (if present). Test control signals from HVAC/PCM to driver and verify driver supply voltages.
If internal motor or driver failure is confirmed, replace the defective component(s) per OEM procedure. For high-voltage e-compressors, follow HV isolation and service procedures or refer to qualified HV technician.
Clear codes, retest system through multiple start/stop and load cycles, and verify the code does not return and A/C function is restored.