P0459 Code: EVAP Purge Control Valve Circuit High
The purge valve control line stays high when the ECU grounds it: a short to power or a shorted solenoid coil.
At a glance
Severity: Low
- Meaning
- EVAP Purge Control Valve Circuit High
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $20–$1,400
- DIY difficulty
- Easy
P0459 is the high-side twin of P0458 and is used mainly by GM and a few other makers. When the ECU switches on the purge solenoid, it pulls the control line to ground and expects the voltage there to drop close to zero with a sensible current. If the line stays high, or the driver detects too much current and shuts itself off to survive, P0459 sets. The usual culprits are a solenoid whose coil has shorted turns and now draws too much current, a control wire rubbing against a powered wire, or moisture bridging the two pins of the connector. The result is a valve that never really opens: the charcoal canister isn't emptied, the engine runs normally, but fuel vapor builds up and the EVAP monitor can't pass.
Can I keep driving? Safe to drive. The engine isn't affected, but the canister slowly saturates, so expect a fuel smell around the car after a few fill-ups. Don't ignore it for months: a shorted coil keeps stressing the ECU driver every time purge is commanded.
How to read P0459
- P Powertrain
- 0 Generic (SAE)
- 4 Auxiliary emission controls
- 59 Specific fault
Symptoms
- Check engine light with the engine running normally
- Gasoline smell near the car, especially after refueling on a hot day
- Purge valve doesn't click when commanded with a scan tool
- EVAP monitor stays incomplete; purge flow code (P0441) may follow
- Purge valve body gets unusually hot after a drive
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Purge solenoid coil with shorted turns, drawing too much current
- Control wire chafed against a powered wire in the same loom
- Water or corrosion bridging the feed and control pins in the connector
- Wrong or low-resistance replacement valve
- ECU output driver damaged by an earlier short
- Feed and control wires swapped after a connector repair
Diagnosis step by step
Measure the coil resistance and compare with spec
Unplug the valve and measure across its pins. Most purge solenoids sit roughly between 15 and 35 ohms. A reading well below the specified value, for example single digits, means shorted turns, which is exactly what makes the driver report a high circuit.
Tools: Multimeter
Check the current draw on the bench
Power the valve from a fused jumper with the meter in series on the amps range. A healthy valve usually draws well under 1 A and clicks crisply. A draw far above that, or a valve that gets hot within seconds, confirms a shorted coil.
Tools: Multimeter
Look for voltage on the control wire with the valve unplugged
With the valve unplugged and the key on, the control wire at the harness should read near zero. If it shows battery voltage, it's shorted to a powered wire somewhere; follow the loom and look for melted or rubbed-through insulation.
Tools: Multimeter
Inspect the connector for moisture
Look for green corrosion or water between the pins, particularly on valves mounted low or near the cowl. Any leakage path between the feed and control pins acts like a partial short to power.
Tools: Flashlight, Soft brush
Verify the replacement part
If the valve was replaced recently, compare its resistance and part number with the original. A valve from a different application may fit the hoses but not match the ECU's expected current.
Tools: Multimeter
Confirm driver operation
With a new or verified valve fitted, command purge with the scan tool and back-probe the control pin: it should drop close to 0 V when on and rise to battery voltage when off. If it stays high even with a good valve and wiring, the ECU driver is suspect.
Tools: OBD-II scanner, Multimeter
Where the parts are
- 1Gas cap
- 2Charcoal canister
- 3Purge valve
- 4Vent valve
- 5Fuel pump
- 6Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace purge solenoid (shorted coil) | Yes | $90–$300 |
| Clean and seal the connector or replace pigtail | Yes | $20–$160 |
| Repair control wire shorted to power | No | $100–$350 |
| Replace saturated charcoal canister if fuel-soaked | No | $200–$600 |
| ECU driver repair or ECU replacement | No | $600–$1,400 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
With P0459 set, the check engine light is on and the EVAP monitor can't complete, so the car fails an OBD-II emissions test. Plan a few days of driving with the tank between a quarter and three-quarters full after the repair so the monitor can run.
Frequently asked questions
What's the difference between P0458 and P0459?
P0458 means the control line sits too low with the valve off, from a missing feed, an open or a short to ground. P0459 is the opposite: the line stays high when the ECU tries to switch the valve on, usually a shorted coil or a short to power.
Can a bad purge valve damage the ECU?
It can. A coil with shorted turns forces the driver to carry too much current. Most drivers protect themselves by shutting off, but repeated overloads can eventually kill the output, so replace the valve promptly.
Why does my car smell of gas with P0459?
Because the purge valve never opens, the charcoal canister keeps absorbing vapor from the tank without being cleaned out. Once it's full, vapor escapes through the vent, and you smell it around the car.
Do I need a new canister as well?
Usually not. Once purge works again, the engine empties the canister over normal driving. Only if liquid fuel reached it, for example from habitual topping off, is a new canister needed.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy