P20A6

Code

Generic P — Powertrain

Reductant Injection Air Pressure Control Valve Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 56 RU: 45

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Malfunction Indicator Lamp (MIL) illuminated and P20A6 stored
Reduced or disabled reductant dosing, possible regeneration/aftertreatment faults
DEF/AdBlue system warning messages on dash
Increased NOx emissions and possible failed emissions test
Possible limp-home mode or reduced engine performance depending on manufacturer

Use a scan tool to read freeze frame, live data, and related DEF/aftertreatment codes
Visually inspect wiring and connectors for damage, corrosion, or water intrusion at valve and ECM
Check for blown fuses and proper relay operation for the DEF/air valve circuit
With ignition off, unplug the valve connector and inspect pins for corrosion, bent pins, or deposits
Check continuity from valve connector to ECM connector for open circuits (backprobe both ends)
Measure resistance of valve solenoid at connector (compare to manufacturer spec)

Valve coil resistance (typical): check service manual; many solenoids are commonly in the range ~10–50 ohms — verify exact spec for vehicle
Control command: ECM typically supplies switched voltage or PWM signal from 0–12V; expected duty cycle varies with dosing demand — verify with scan tool
Voltage at valve connector with system commanded ON: should show battery voltage or PWM waveform (battery-referenced)
Expected current draw when activated: typically under a few amps; an open circuit will show infinite resistance/no current
If available, live data should show valve commanded state (ON/OFF or duty %) and any air pressure sensor readings — compare to expected values

Retrieve all related codes and freeze-frame data with a scan tool; note vehicle operating conditions when code set.
Visually inspect harness, connectors, and valve for damage, corrosion, or contamination; repair or clean as needed.
Check fuses and relays for the DEF/air valve circuit; replace any blown fuses or faulty relays and retest.
With ignition OFF, disconnect valve connector and measure solenoid resistance across terminals. If open/infinite resistance, replace valve.
Check continuity between valve connector and ECM pin for both power/control and ground. Repair any open circuits found.
With connector safely back-probed and ignition ON, command the valve ON using a scan tool and measure voltage/PWM at the connector. If command signal present but valve not actuating, suspect valve failure.
If no command signal from ECM, trace back to ECM, check grounds, fuses, relays, and inspect for wiring shorts to battery/ground. Consider ECM driver fault if wiring and peripherals are good.
After repair, clear codes, cycle key and run vehicle to verify proper operation and that P20A6 does not return. Re-run diagnostics and confirm live data and DEF dosing behavior.
If intermittent, perform wiggle tests and road test (or run self-tests) to reproduce. If problem persists with correct wiring and known-good valve, consult OEM technical service for ECM-level diagnostics or updates.