What does it mean?
On vehicles equipped with Evaporative Emission Control (EVAP) systems, the engine draws excess fuel vapors from the gas tank that would otherwise be released into the atmosphere. The purpose of the system is to reduce vehicle emissions.
The evaporative emission system consists of the fuel tank, a vapor line to the charcoal canister to contain fuel vapors, a pressure sensor on the fuel tank, a purge valve on the charcoal canister, a vapor line to the fill neck shut-off valve, and a vapor line from the charcoal canister purge valve to the intake manifold. When the engine is off, the vent shut-off valve and the tank purge valve are closed.
Fuel cannot escape into the atmosphere. When the engine starts, the purge valve on the tank opens to allow the trapped fuel vapor to be drawn by engine vacuum into the intake manifold. At the same time, the vent shut-off valve also opens to allow a small amount of air to enter the tank and mix with the fuel vapor for a better mixture. Once purged and the pressure sensor in the tank shows a significant drop, both valves close again, sealing the system.
The fuel vapor is routed via a vacuum line to the engine intake, and the purge valve/solenoid measures the desired amount of fuel vapors, controlled by the Powertrain Control Module (PCM) or Engine Control Module (ECM). The PCM/ECM monitors the voltage to the purge control valve and detected a higher voltage than expected.
Related purge control valve circuit codes include:
P0443 Evaporative Emission Control System Purge Control Valve Circuit
P0444 Evaporative Emission Control System Purge Control Valve Circuit Open
P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted
P0458 Evaporative Emission System Purge Control Valve Circuit Low
Symptoms
Visible symptoms of a P0459 EVAP trouble code typically include only the illumination of the Malfunction Indicator Lamp (MIL) or the “Check Engine/Service Engine Soon” light. Other trouble codes may accompany this code. In some cases, there may be a gas smell and/or a slight decrease in fuel efficiency.
Potential Causes
Causes
of this DTC may include:
Blown fuse or relay
Faulty purge control valve
Faulty EVAP purge solenoid control
Electrical wiring issue in the engine wiring harness or connector
Electrical circuit problem in the purge control solenoid
PCM/ECM malfunction
Diagnosis and Repair
A good first step if you receive a P0459 is to check for Technical Service Bulletins (TSBs) that apply to your vehicle’s year/make/model. If it is a known issue, a TSB can save you time and money during diagnosis and repair.
Visually inspect the engine wiring harness connectors for any damage, look for pinched wires, loose or bent pins, or bare wiring without insulation. Typically, the purge control valve is powered by the battery and triggered on and off with a duty cycle via the PCM/ECM. Using the manufacturer’s wiring diagrams, identify the type of circuit used and check for battery voltage with the key on/engine off on the power side of the control solenoid connector using a Digital Volt-Ohm Meter (DVOM) set to the volts scale. If no battery voltage is present, trace the wiring to determine the cause.
Check for a short to ground by disconnecting the harness at the control valve solenoid and the voltage source. Using the DVOM set to the ohms scale, with the negative lead connected to a known good ground and the positive lead to each end that powers the control valve solenoid. If the resistance is very low, suspect a short to ground and repair the wiring harness. Check for a short to ground on the control side of the harness by disconnecting the harness from the control valve solenoid and the PCM/ECM harness. Identify the correct wire and using the DVOM set to an ohms scale, check the resistance with the negative lead connected to a known good ground and the positive lead on one of the control circuit wire harnesses. If the resistance is very low, suspect a short to ground and repair the wiring harness.
Purge Control Solenoid – Check for continuity at the purge control solenoid connector pins after removing the plug from the harness using the DVOM set to the ohms scale. Verify that the resistance meets the manufacturer’s specifications. Check for a short to ground using the DVOM with the negative lead attached to a known good ground and the positive lead on each of the control valve solenoid terminal pins. The resistance should be very high or above the limit (OL). If very low resistance is detected, suspect that the control valve solenoid is shorted to ground and replace it with a known good unit.
Since the EVAP system only activates under certain driving conditions, it will be necessary to monitor the EVAP control operation using a capable advanced scan tool and perform a road test under the required driving conditions to activate the EVAP system. Some advanced scan tools have an internal test to manually activate the EVAP system. Verify that the PCM/ECM is commanding the EVAP system. If the system is operating correctly, it will be necessary to probe the PCM/ECM wiring harness connector using a graphing multimeter or an oscilloscope with a duty cycle function, with the positive lead on the purge control valve pin and the negative lead connected to a known good ground source. The duty cycle should match what is commanded by the PCM/ECM during EVAP operation. If no duty cycle is present, the PCM/ECM may be faulty.