P20A3

Code

Generic P — Powertrain

Reductant Purge Control Valve A Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 28 EN: 41 RU: 30

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Page language: EN

Causes

Open or shorted wiring in reductant purge valve A circuit
Corroded, loose, or damaged connector at the purge valve or module
Short to battery voltage on the valve control wire
Faulty reductant purge control valve (internal short or failed driver coil)
Blown fuse or faulty relay in the reductant control supply circuit
Poor ground or chassis connection

Symptoms

MIL / Check Engine Light illuminated
Reduced or disabled reductant purge function; possible SCR system warnings
Possible engine derate or restricted operation in emission control strategy
Failed SCR system readiness / failed emissions test
Noisy or non-operational purge valve (depending on failure mode)

What to check

Read freeze-frame data and other related codes (SCR/NOx/reductant system)
Visual inspection of wiring harness, connector, and valve for damage or corrosion
Check fuses and relays for the reductant control circuit
Measure voltage at the valve connector with ignition ON and while commanding the valve
Measure coil resistance of the purge valve with the connector disconnected
Check continuity to PCM and for shorts to battery or ground

Signal parameters

Coil resistance (valve disconnected): typically in the order of 5–30 ohms (vehicle-dependent) — compare to spec
Inactive/reference voltage at valve positive: near battery voltage (~11–14 V) if circuit is high-side supplied
When PCM controls by low-side switching: energized driver will show low voltage to ground at the control terminal (near 0–1.5 V) or PWM signal
When PCM controls by high-side switching: energized terminal shows battery voltage when activated
Diagnostic threshold: 'Circuit High' indicates measured control voltage is higher than the PCM expected range (often indicating a short to battery or open circuit in the return path)

Diagnostic algorithm

Retrieve and record freeze frame data, all related DTCs, and current reductant/SCR status.
Perform a thorough visual inspection of the valve, harness, and connector for damage, corrosion, loose pins, or fluid contamination.
Check fuses and relays related to the reductant/SCR system; replace if blown or faulty.
With ignition ON (engine OFF), backprobe the purge valve connector and measure voltage on the control and supply terminals; note voltages with valve commanded ON and OFF using a scan tool.
Disconnect the valve and measure coil resistance across the valve terminals; compare to specification. Very high/infinite resistance indicates open coil; very low indicates short.
Check continuity from the valve connector to the PCM connector for the control and supply circuits; check for short to battery or ground using an ohmmeter.
If a short to battery is suspected, isolate wiring sections and inspect for chafing or pinched insulation; repair or replace damaged harness.
If wiring and valve check OK, command the valve while monitoring PCM output with a lab scope or multimeter to verify proper switching/PWM; if PCM output remains high with no load, suspect module driver failure.
If available and after verifying wiring, install a known-good valve to confirm whether the original valve is faulty.
After repairs, clear codes and perform functional tests and a road/regeneration cycle if required; recheck for return of the code.

Likely causes

Short to battery on the valve control wire or damaged insulation
Failed or internally shorted purge control valve
Connector corrosion or poor pin contact at valve
Blown fuse or faulty relay in SCR/control circuit
PCM/ECM driver fault (less common)

Fault status

⚠️ Status

P20A3 — Reductant Purge Control Valve A Circuit High: electrical fault detected (voltage higher than expected) on reductant purge valve A control circuit. Inspect wiring, connectors, valve, fuses/relays, and PCM driver.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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