EVAP Purge Flow Output - Abnormal Reading
The engine control module detected an abnormal reading from the EVAP purge system.
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What it means (plain English)
The engine's computer is getting a signal that something's wrong with how the fuel vapor canister is letting fuel vapors into the engine for burning. This could mean either the valve itself is stuck or malfunctioning, or there's an issue in the system allowing vapor to escape when it shouldn't.
What the computer is actually seeing
The engine control module (ECM) monitors the internal state of the EVAP purge flow valve by measuring the resistance and voltage signals coming from it, typically expecting a voltage between 0.5V and 4.5V when activated. If it sees something significantly out of this range or inconsistent readings during a self-test, it triggers a fault code.
What a healthy reading looks like
Optimally, the purge valve should operate between 0.5V (closed) and 4.5V (fully open). When opened at idle, expected flow rate is typically 1 to 2 grams of fuel vapors per min.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check for damaged or loose vacuum connections to the EVAP purge valve.
- 2Inspect wiring to the EVAP purge valve for frays or breaks; should have continuity with no shorts.
- 3With the engine on, measure voltage at the EVAP purge valve connector; should be between 0.5V and 4.5V.
- 4Apply vacuum directly to the EVAP purge valve; it should open and allow flow; if it doesn't, replace the valve.
- 5Check for leaks in the EVAP system with a smoke tester; look for any sources of vacuum loss or blockage.
- 6Clear the code and drive cycle to see if the code returns. If it does, consider replacing the ECM.
Common causes
- Faulty EVAP purge valve
- Leaking vacuum hose
- Blocked EVAP canister
- Wiring issue in the EVAP circuit
- Faulty ECM
- Blocked fuel tank vapor vent line
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code present?
Yes, it's usually safe to drive, but the vehicle may not pass emissions testing.
Will this code come back after clearing?
If the underlying issue isn't fixed, yes, it will likely return.
Does this code pair with any other codes?
Yes, it's often seen with codes related to the EVAP system like SPN 3396 and SPN 3398.
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