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P0405 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

DTC Code P0405: Exhaust Gas Recirculation Sensor (Circuit A) Low

Meaning

The diagnostic trouble code P0405 indicates that the Exhaust Gas Recirculation (EGR) position is below the specifications of the Powertrain Control Module (PCM). This usually happens when the EGR sensor has an internal open circuit.

As the name suggests, the primary function of the EGR position sensor is to detect the position of the EGR valve. Meanwhile, the EGR valve is programmed to carry exhaust gas to the engine without using the intake manifold vacuum. This valve controls the flow of the exhaust gas into the intake manifold from the exhaust manifold. This is carried out via an orifice with a PCM-controlled pintle.

Using the data received from the Throttle Position (TP) sensor, the Manifold Absolute Pressure (MAP) sensor, and the Engine Coolant Temperature sensor, the PCM controls the pintle position. The PCM equally commands the EGR valve in order to supply the correct amount of exhaust gas recirculation for the current engine operating conditions. If during this process, the PCM detects a sensor signal which deviates from the specified reading, then the vehicle records a P0405 code and the Check Engine Light (CEL) is ignited.

Causes

The occurrence of this trouble code in your vehicle has to do with a defective Exhaust Gas Recirculation (EGR) Sensor or its components. Meanwhile, a number of malfunctions in the EGR system could prompt your vehicle to record this code. The most common of these include:

  • Defective EGR valve position sensor
  • Damaged EGR valve
  • Blocked or clogged EGR pathway
  • Defective Differential Pressure Feedback EGR (DPFE) sensor
  • Defective EGR volume control solenoid valve
  • Accumulation of carbon on the EGR valve
  • Shorted or opened EGR volume control solenoid valve harness
  • Poor electrical connection at the EGR volume control solenoid valve circuit
  • Defective EGR temperature sensor and circuit
  • Loose or broken terminals towards the PCM
  • Spoilt or defective vacuum line

Symptoms

While this code indicates defects in the EGR sensor or its components, there are a number of symptoms that are used in detecting the presence of this code in a vehicle. These symptoms vary from mere illumination of the CEL to a more serious symptom such as stalling. A vehicle having one or more of the problems below is sure to have a DTC code P0405 trouble:

  • Illumination of the Check Engine Light (CEL)
  • Stalling of the engine
  • Rough running
  • Engine pre-ignition on acceleration
  • Failed emission test as a result of increased emission of Oxides of Nitrogen (NOx)
  • Reduced engine performance
  • Increased fuel consumption

Diagnosis

This could be a DIY diagnosis especially when you have had a similar experience. The diagnosis requires experience using the OBD-II scanner to read the freeze frame data.

To successfully diagnose your vehicle of this code, you require a specific Electric Vehicle Diagram (EVD) which corresponds with your vehicle make or model. Also, you need an OBD-II scanner to scan and read the freeze frame data, and a Digital Multimeter (DMM).

It is important to note that the use of an OBD-II scanner is mostly recommended for this diagnosis. Nevertheless, a DMM can be used when the OBD-II scanner is unavailable. With these tools on standby, ensure that your car battery charger is connected before you begin the diagnosis.

  • First thing first, connect the OBD-II scanner and download the freeze frame data related to EGR
  • Then proceed by visually inspecting the wire connections to check for damage or burns 
  • Also, inspect for possible water damage or broken pins, repair the connection of any damages detected
  • Proceed by conducting a visual inspection on the EGR sensor connector, checking for corrosion
  • Next is to inspect the EGR position sensor. Should your vehicle’s EGR valve be vacuum-actuated, then you need to conduct a position sensor test using a vacuum pump and DMM
  • Then proceed to remove the connector and take note of the resistance over the entire circuit. You should get about 6kΩ as your reading
  • For Electronically actuated EGR, check the output voltage using the DMM to scan the connector on the rear and note the voltage. Ensure that the vehicle is in Key ON Engine OFF during this process
  • If the voltage in this system deviates from the specifications of the PCM, then there is either a short circuit or a damaged sensor
  • Repair the circuit and sensor, or replace if a repair doesn’t fix the damage
  • Having completed the steps above, clear the code and take the vehicle for a road test to see if the code returns
  • If the code returns, observe the EGR sensor PID (Performance Information Data) on the OBD-II scanner, checking if the sensor indicates that the valve is in the correct closed position or the sensor voltage returns below specifications
  • Connect both the sensor reference voltage and signal return pins together and check the scanner to show reference voltage on the EGR sensor PID
  • Lastly, replace the EGR sensor or repair wiring as required, then check the system again for proper readings

Common mistakes

A common diagnostic mistake when dealing with P0405 is the failure to connect both the sensor reference voltage and signal return pins together. This is to check if all the wiring is good before replacing the EGR position sensor. Also, technicians may fail to check the wiring harness and connection to the EGR position sensor for shorted or open circuits before replacing the EGR position sensor.

How serious is this?

Although many technicians regard this trouble code as not so serious, its damaging effects in a vehicle call for immediate attention. If this code is active for long, the PCM may deactivate the EGR system and becomes dysfunctional. In addition, the illumination of CEL may cause the vehicle to fail the emission test. As the position of the EGR is critical for the PCM to properly control the EGR valve opening and closing, it can also cause rough running and stalling of the engine.

What repairs can fix the code?

Repair manuals

In addition to the diagnosis above, the following repairs can also be carried out to effectively clear your vehicle of this code:

  • Consider replacing the EGR Valve
  • Consider replacing the EGR position sensor
  • Clean the EGR position sensor
  • Inspect the voltage at the EGR system
  • Look out for a vacuum towards the EGR system
  • Repair any vacuum leaks observed
  • Visually inspect the wiring to the EGR sensor to check for loose connection and ensure that the connection is secure

Related codes

This trouble code is related to other codes that are related to EGR, these include;

  • P0400 – Exhaust Gas Recirculation Flow Malfunction
  • P0401 – Exhaust Gas Recirculation Flow Insufficient Detected
  • P0402 – Exhaust Gas Recirculation Excessive Flow
  • P0403 – Exhaust Gas Recirculation “A” Control Circuit Malfunction
  • P0404 – Exhaust Gas Recirculation Circuit Range/Performance
  • P0406 – Exhaust Gas Recirculation Sensor A Circuit High

Conclusion

DTC Code P0405 is recorded when the EGR position deviates from the PCM specifications. Although with the information given above, this code can be cleared without the attention of an expert technician if you have a good OBD-II scanner and follow the step wise instructions to troubleshoot the code. However, having expert conduct the diagnosis may be safer if you are a rookie. Also, having this code tarry in your vehicle before fixing could lead to other problems and even prompt your vehicle to record another code. In a nutshell, we recommend that you pay immediate attention to every OBD-II regardless of the severity.

P0405 code – what does it mean & how to fix it

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