P0468
Purge Flow Sensor Circuit High InputP0468 is a generic OBD-II powertrain diagnostic trouble code: Purge Flow Sensor Circuit High Input. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0468 means
P0468 — Purge Flow Sensor Circuit High Input — is the electrical complement to P0467. The PCM has detected a signal from the purge flow sensor that is at or above the maximum valid threshold — a value that cannot represent any real flow condition within the system's physical limits. On voltage-output sensors this means the signal rail is pulled toward the supply voltage; on frequency-output designs the pulse rate is abnormally high or saturated.
The most common electrical cause on voltage-type sensors is an open circuit: when the signal return path is broken, the PCM's internal pull-up resistor (if fitted) or floating input rail reads near the reference voltage, which the module interprets as a maximum-flow or out-of-range high reading. An internally open sensor element produces the same result. A short between the signal wire and the reference supply wire also forces the signal high.
On some platforms P0468 can be triggered by an EVAP system large leak that draws excessive air through the purge path during a commanded purge event, producing a flow reading above the sensor's calibrated upper range. This is a minority cause but is worth ruling out with a smoke test after electrical checks pass.
The consequence is the same as for P0465 and P0467 — EVAP purge monitoring is degraded, the MIL is on, and the vehicle will fail an emissions inspection. There is no limp mode or immediate safety concern on any standard platform.
Common causes
Most-frequently reported root causes when P0468 is logged.
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1
Open circuit in the sensor signal wire — floating input read as high by PCM pull-up.
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2
Internal open in the purge flow sensor element — no return path causes the signal to float high.
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3
Short between the signal wire and the sensor reference supply wire.
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4
Corroded or backed-out pin at the sensor connector leaving the signal rail floating.
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5
Broken wiring harness (heat damage, mechanical fatigue) between sensor and PCM.
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6
Large EVAP system leak drawing excessive air through the purge path during purge events, driving flow reading above the sensor's calibrated maximum (less common).
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7
PCM internal input circuit fault holding the signal line high (rare; only after all external causes are excluded).
Symptoms drivers notice
How to diagnose P0468
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and observe the PFS live-data PID — a reading pegged at maximum with the engine running before any purge event confirms the fault is active.
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2
With KOEO and the sensor connected, measure signal voltage at the harness connector; a voltage near the reference rail (5 V) confirms a high fault.
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3
Disconnect the sensor: if the signal voltage drops significantly with sensor disconnected, the sensor element is internally open or shorted to supply; if it remains high, the fault is in the wiring (short to reference).
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4
Inspect the harness from sensor to PCM for any point where the signal wire may contact the reference supply wire (chafing in a shared loom).
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5
Check the sensor connector for backed-out, corroded, or spread pins that break the signal return path.
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6
If electrical checks pass, perform an EVAP smoke test to rule out a large system leak producing abnormally high measured flow.
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7
Replace the purge flow sensor if internal open is confirmed and harness is serviceable.
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8
After repair, command purge solenoid open and verify PFS PID reads a plausible value within the expected flow range.
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Why does an open circuit cause a HIGH reading on the flow sensor?
Most PCMs have a weak pull-up resistor on sensor signal inputs. When the signal wire is broken or the sensor element is open, the input node is pulled toward the reference voltage by this internal pull-up, producing a near-maximum reading. The PCM recognises this value as outside the valid range and sets P0468. If the PCM lacks a pull-up, the input floats and reads erratically, but either way the value exceeds the valid window.
Is P0468 more or less urgent than P0467?
Both codes completely disable valid purge flow feedback and both set the MIL, so urgency is equivalent from an emissions perspective. Repair priority is the same: diagnose and repair promptly to restore EVAP monitoring and pass emissions inspections.
Can P0468 appear alongside a large EVAP leak code?
Yes. A large leak (P0455) can produce an abnormally high flow reading during commanded purge because air rushes in through the leak path, driving measured flow above the sensor's calibrated maximum. In this scenario fixing the EVAP leak may clear P0468 without any sensor or wiring repair needed. Always check for and resolve large leak codes first.
Disabling P0468 in software
RaceTune can permanently disable P0468 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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