P1426 – Evaporative emission (EVAP) canister purge valve – open circuit (Audi)

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By Reinier (Contact Me)
Last Updated 2023-06-26
Automobile Repair Shop Owner
CodeFault LocationProbable Cause
P1426 P1426 – Evaporative emission (EVAP) canister purge valve – open circuit (Audi)
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Manufacturer Specific Definitions for P1426

MakeFault Location
AudiEvaporative emission (EVAP) canister purge valve - open circuit
CitroenEGI Mini - MAF Failed Out Of Range
PeugeotEGI Mini - MAF Failed Out Of Range
VolkswagenEvaporative emission (EVAP) canister purge valve - open circuit

Table of Contents

  1. What Does Code P1426 Mean?
  2. Where is the P1426 sensor located?
  3. What are the common causes of code P1426?
  4. What are the symptoms of code P1426?
  5. Get Help with P1426

What Does Code P1426 Mean?

OBD II fault code P is a manufacturer-specific trouble code that is defined by carmaker Audi as P1426 – “Evaporative emission (EVAP) canister purge valve – open circuit”, and is set when the PCM (Powertrain Control Module) detects an open circuit in the wiring that controls the EVAP purge valve.

The function of all EVAP systems is to trap and contain fuel vapors in the fuel system of the vehicle until the vapor pressure reaches a predestined threshold. When this point is reached, the fuel vapors are purged from the fuel system, and transported to the engine to be combusted as part of the air/fuel mixture. Here is a generic description of how EVAP systems work-

Since fuel, and especially gasoline is highly volatile, the vapors that result from the evaporation and agitation of the fuel used to escape into the atmosphere through vented fuel filler caps. However, as emissions regulations became more stringent, car manufacturers began devising systems to trap and contain the fuel vapors to prevent the vapors from escaping from the fuel system.

So, while there are significant differences between the design and operating principles of EVAP systems in use today, all EVAP systems are designed to seal the fuel system in order for a charcoal-filled canister to absorb all fuel vapors. Moreover, apart from a charcoal canister, all EVAP systems also have vent valves to allow atmospheric air to enter the system during purging and a separate purge valve that allows collected fuel vapors to flow toward the engine through dedicated vapor lines.

In addition, all EVAP systems also use fuel vapor pressure sensors to monitor the vapor pressure in the fuel system, and in some cases, these sensors are also used to detect vapor leaks in the EVAP system.

In terms of operating principles, the PCM seals the fuel system by keeping both the vent and purge valves closed, but when the vapor pressure reaches a maximum allowable limit, the PCM will command both the vent and purge valves open, to allow the engine vacuum to draw the fuel vapors out of the tank and charcoal canister. To improve the evacuation process, atmospheric air that enters the system through the open vent valve “pushes” fuel vapor from the charcoal canister, but once the fuel vapor pressure diminishes to below a certain threshold, the PCM closes both the vent and purge valves to seal the fuel system again.

For diagnostic and emission control purposes, the PCM does not only monitor the operation of the EVAP system continuously but also performs periodic self-diagnostic tests to check the system for vapor leaks. These tests involve either evacuating the fuel tank, or pressurizing the tank with a dedicated air pump, but regardless of the method employed, both the vent and purge valve perform critical functions during these tests since both valves contribute towards the effective sealing of the fuel system.

Based on the above, it should be obvious that if the purge valve does not work as expected, the PCM cannot a) perform self-diagnostic tests, or b) control the operation of the EVAP system effectively in terms of purging fuel vapors from the fuel system.

Thus, should a failure, malfunction, or defect exist in either the purge valve itself, or in the wiring that controls the valve, the PCM will recognize that it cannot control or manage the EVAP system effectively, and it will set code P1426 and illuminate a warning light as a result.

Where is the P1426 sensor located?

The image above shows the location (arrowed) of the EVAP purge valve on a 2014 Audi A4, but note that this location is not representative of EVAP purge valves on all Audi models.

In many cases, the purge valve may be located elsewhere in the engine compartment or it may be located close to either the fuel tank or the charcoal canister under the vehicle. Moreover, since EVAP purge valves on Audi and related models come in a great variety of designs and shapes, we strongly recommend that you research the exact location of the EVAP purge valve on an affected vehicle before attempting a diagnostic or repair procedure that involves the EVAP system.

Alternatively, we recommend that you seek professional assistance with diagnosing and resolving EVAP system issues to avoid confusion, misdiagnoses, and/or damage to the EVAP system where there was none before.

What are the common causes of code P1426?

Some common causes of code P1426 could include one or more of the following-

• Damaged, burnt, corroded, or disconnected wiring and or electrical connectors in the purge valve’s wiring
• Damaged or malfunctioning EVAP purge valve

What are the symptoms of code P1426?

Note that since EVAP purge valves are held in the closed position by spring tension until they are commanded open by the PCM, it is highly unlikely that an open circuit would cause the valve to become stuck in the open position. Therefore, the most common symptoms of code P1426 could include one or more of the following-

• Stored trouble code and an illuminated warning light
• Depending on the nature of the problem, one or more additional codes may be present along with P1426
• Some vacuum and vapor lines may become dislodged as a result of excessive vapor pressure in the fuel system
• The EVAP readiness monitor will not initiate or run to completion because the PCM cannot perform leak tests on the EVAP system
• The vehicle will not pass a mandatory emissions test

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