Technical Description of OBD-II Trouble Code
Low Flow in Evaporative Emission System Leak Detection Reference Orifice
What does that mean?
This is a generic diagnostic trouble code (DTC) that typically applies to OBD-II vehicles equipped with an EVAP system that utilizes a leak detection system. This can include vehicles from Toyota, Scion, GM, Chevrolet, Hyundai, Pontiac, Volvo, and others. Toyota vehicles seem to experience this code more frequently. The exact repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
Your OBD-II vehicle has stored a code P043E, indicating a discrepancy in the evaporative emissions system (EVAP) leak detection reference orifice. Specifically, a low flow condition has been detected.
The EVAP system is designed to capture fuel vapors from the fuel tank before they are released into the atmosphere. It uses a vented reservoir, also known as a canister, to store excess vapors until the engine is operating under conditions that allow for efficient burning of the vapors.
The pressure created by the stored fuel acts as a propellant, causing the vapors to vent through tubes and into the canister. The canister contains a charcoal element that absorbs the fuel vapors and releases them at the appropriate time.
The EVAP system typically includes various sample orifices, a leak detection pump, a charcoal canister, an EVAP pressure sensor, a purge valve/solenoid, a vent control valve/solenoid, and a complex system of metal tubes and rubber hoses that stretch from the fuel tank to the engine compartment.
The EVAP system uses engine vacuum to draw fuel vapors from the charcoal canister and through the lines into the intake manifold, where they can be burned instead of being released into the atmosphere. The purge control valve/solenoid, which is controlled by the PCM, regulates intake vacuum to the EVAP canister to ensure that fuel vapors are drawn into the engine only when conditions are optimal for efficient burning.
Some EVAP systems use an electronic leak detection pump to pressurize the system for leak and flow testing. Leak detection reference orifices may be placed at various points in the EVAP system. These orifices are typically in-line filters that allow for accurate measurement of flow when the leak detection pump is activated. The PCM uses input signals from EVAP pressure and flow sensors, along with the leak detection reference orifice(s), to determine if the leak detection system is functioning correctly. The EVAP leak detection reference orifice may be a small filter or simply a restricted area in the EVAP line that allows an EVAP pressure/flow sensor to obtain an accurate sample.
If the PCM detects a low flow condition through the EVAP leak detection reference orifice, it will store a code P043E and may illuminate the malfunction indicator lamp (MIL).
What is the severity of this DTC?
EVAP leak detection codes, including P043E, specifically relate to the evaporative emission control system and are not considered severe.
What are some of the symptoms of the code?
A P043E trouble code is unlikely to cause noticeable symptoms. However, you may experience slightly reduced fuel economy and other EVAP leak detection diagnostic codes.
What are some of the common causes of the code?
Possible causes of this P043E engine code include:
What are some P043E troubleshooting steps?
To diagnose a code P043E, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and reliable vehicle information. It is recommended to check for technical service bulletins (TSB) that match the symptoms and codes of the vehicle being diagnosed. These bulletins can provide guidance on identifying the source of the malfunction.
If there are other EVAP system codes present, address and repair those before attempting to diagnose the P043E code. The P043E code may be a reaction to conditions that have caused other EVAP codes.
Before starting the diagnosis, connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. This information can be helpful during the diagnosis process. After retrieving the data, clear the codes and test-drive the vehicle to see if the code is reset.
During the test drive, monitor the vehicle until one of two things happens: the PCM enters readiness mode or the code is reset. If the PCM enters readiness mode, it indicates an intermittent problem or a potential inadvertent repair. If the code is reset, it confirms a definite malfunction that needs to be addressed.
Begin the diagnosis with a visual inspection of any accessible EVAP system wiring harnesses and connectors. Focus on areas with high temperatures and areas where wiring, connectors, vacuum lines, and vapor hoses may interfere with moving components. Many vehicle issues are resolved during this inspection phase, so pay attention and put effort into it.
Connect the scanner to the vehicle diagnostic port and observe the data stream. When the EVAP system is activated, the EVAP flow and pressure data should meet the manufacturer’s specifications. In most cases, you can activate the EVAP system (purge control solenoid and/or leak detection pump) using the scanner. Some EVAP sensor testing may need to be performed with the system activated.
Use the DVOM to test the EVAP sensors and solenoids and compare the readings to the manufacturer’s specifications. Replace any components that do not align with the specifications. If possible, inspect the EVAP leak detection reference orifice for charcoal contamination, as this may indicate a compromised EVAP canister.
Before testing the system circuits with the DVOM, disconnect any related controllers to prevent damage. Test the resistance and continuity between individual EVAP components and the PCM using the DVOM. Repair or replace any circuits that do not align with the specifications.
