Technical Description of OBD-II Trouble Code
The circuit for the control valve of the Evaporative Emission System Purge is experiencing high voltage.
This code is a generic OBD-II code that applies to vehicles equipped with OBD-II, including Hyundai, VW, Chevrolet, Audi, Kia, Volvo, BMW, etc. It is more commonly observed in Subaru and Ford models. The specific repair steps may vary depending on the vehicle’s year, make, and model.
What does that mean?
In vehicles equipped with evaporative emission control systems (EVAP), the engine draws in excessive fuel vapors from the gas tank instead of venting them into the atmosphere. This system is designed to reduce vehicle emissions.
The evaporative emission system consists of the fuel tank, a vacuum hose connected to the charcoal canister for containing the fuel vapors, a pressure sensor on the fuel tank, a purge valve on the charcoal canister, a vacuum hose connected to the filler neck shut off valve, and a vacuum hose from the charcoal canister purge valve to the intake manifold. When the engine is off, both the vent shutoff valve and canister purge valve are closed.
This prevents fuel from escaping into the atmosphere. When the engine starts, the purge valve on the canister opens, allowing the trapped fuel vapor to be drawn into the intake manifold by engine vacuum. At the same time, the vent shutoff valve also opens, allowing a small amount of air to enter the canister and mix with the fuel vapor for a better mixture. Once the fuel vapor is vented and the pressure sensor in the tank detects a significant drop, both valves close, sealing the system once again.
The fuel vapor is routed through a vacuum line to the engine’s intake, and the purge valve/solenoid controls the desired amount of fuel vapors. This is controlled by the vehicle’s powertrain control module (PCM) or engine control module (ECM). The PCM/ECM monitors the voltage to the purge control valve and has detected a higher voltage than expected.
Other related purge control valve circuit codes include:
Symptoms
The noticeable symptoms of a P0459 EVAP trouble code typically include the illumination of the malfunction indicator lamp (MIL) or “Check Engine Light / Service Engine Soon” light. Other trouble codes may accompany this code. In some cases, there may be a smell of gas and/or a slight decline in fuel efficiency.
Potential Causes
The causes of this DTC may include:
Diagnosis & Repair
A good first step if you receive a P0459 is to check for Technical Service Bulletins (TSBs) that apply to your year/make/model. If this is a known issue, a TSB can help save you time and money during diagnosis & repair.
Visually inspect the engine wiring harness connectors for damage, look for pinched wires, loose or bent pins, or bare wiring with no insulation. Typically, the purge control valve is energized by the battery and triggered on and off with a duty cycle through the PCM/ECM. Using the manufacturer’s wiring diagrams, identify which type of circuit is being used and check for the presence of battery voltage with the key on/engine off at 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 back to determine the cause.
Check for a short to ground by disconnecting the harness at the control valve solenoid and the source of voltage. Using the DVOM set to the ohms scale, with the negative lead connected to a known good ground and the positive lead on either end that supplies power to 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 the ohms scale, check for resistance with the negative lead connected to a known good ground and the positive lead on either wire harness for the control circuit. 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 harness plug using the DVOM set to the ohms scale. Verify that the resistance is within 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 terminal pins to the control valve solenoid. The resistance should be very high or over limit (OL). If there is a very low amount of resistance found, suspect that the control valve solenoid is shorted to ground and replace it with a known good unit.
Since the EVAP is only turned on during certain driving conditions, it will be necessary to monitor the EVAP control operation using an advanced scan tool capable of performing a road test under the driving conditions required 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 on. If the system is functioning correctly, it will be necessary to back probe the PCM/ECM wiring harness connector using a graphing multimeter or oscilloscope with a duty cycle feature, with the positive lead on the purge control valve pin and the negative lead connected to a known good ground. The duty cycle should match what is commanded on by the PCM/ECM during EVAP operation. If there is no duty cycle present, the PCM/ECM may be at fault.
