Open or damaged wire in the EGR circuit, especially at the connector or where the harness bends near the engine; Failed EGR valve position sensor or integrated EGR valve assembly; Corroded or loose electrical connector at the EGR valve; Poor ground connection for the EGR circuit or engine block; Faulty engine control module (less common but possible after other causes are ruled out); Carbon buildup causing the valve to stick, which can skew the position sensor signal high

DTC codes / Subaru codes / P1421

P1421 · SubaruExhaust Gas Recirculation Circuit High Input

Q: What does code P1421 mean?

Exhaust Gas Recirculation Circuit High Input. P1421 on a Subaru means the engine control module has detected an abnormally high voltage on the exhaust gas recirculation circuit, which usually points to an open circuit or a failed sensor rather than a stuck valve. The computer monitors the EGR (exhaust gas recirculation) system's electrical feedback and sets this code when the signal stays above the expected threshold for a calibrated time.

P1421 on a Subaru means the engine control module has detected an abnormally high voltage on the exhaust gas recirculation circuit, which usually points to an open circuit or a failed sensor rather than a stuck valve. The computer monitors the EGR (exhaust gas recirculation) system's electrical feedback and sets this code when the signal stays above the expected threshold for a calibrated time.

SystemPowertrain

Code typeSubaru specific

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Slight hesitation or stumble during light-throttle acceleration
Rough idle or intermittent idle fluctuation
Reduced fuel economy over time
Failed emissions inspection due to the check engine light
In rare cases, a noticeable ping or knock under load if EGR flow is completely lost

Common causes, most likely first

Open or damaged wire in the EGR circuit, especially at the connector or where the harness bends near the engine
Failed EGR valve position sensor or integrated EGR valve assembly
Corroded or loose electrical connector at the EGR valve
Poor ground connection for the EGR circuit or engine block
Faulty engine control module (less common but possible after other causes are ruled out)
Carbon buildup causing the valve to stick, which can skew the position sensor signal high

How to diagnose and fix it

Inspect the EGR valve connector and wiring for corrosion, chafing, or loose pins, and repair as needed
Check the EGR circuit ground and power supply with a multimeter to confirm voltage and continuity
Measure the resistance of the EGR valve position sensor and compare to Subaru specifications
Backprobe the signal wire at the EGR valve and observe voltage while commanding the valve with a scan tool
Remove and clean the EGR valve and passages if carbon buildup is present, then retest
Replace the EGR valve assembly if electrical tests confirm an internal sensor failure
Clear the code and perform a drive cycle to verify the repair, addressing any remaining wiring issues if the code returns

What most Subaru owners miss about P1421

A high input code often means an open circuit, not a stuck valve, so replacing the EGR valve without checking wiring first is a common and expensive misdiagnosis.
Subaru EGR valves on some models are integrated with the position sensor, so a sensor failure requires replacing the entire valve assembly rather than a separate sensor.
Carbon buildup inside the EGR valve can cause the position sensor to read high even when the electrical circuit is intact, so cleaning the valve is sometimes the only repair needed.
The engine control module rarely fails, but a shorted sensor or water intrusion into the connector can mimic a module fault, so always rule out the harness before condemning the computer.
This code can be set by a poor engine ground that affects the EGR circuit reference voltage, which is often overlooked during diagnosis.

Can I keep driving with P1421?

You can usually drive the car short distances to a repair shop, but avoid sustained highway driving or heavy loads because a faulty EGR system can cause pinging and increased emissions. If the check engine light starts flashing or you notice severe hesitation, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for Subaru vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.