Fault code P040B – exhaust gas recirculation temperature sensor “A” circuit range/performance

Fault code P040B is called “Exhaust Gas Recirculation (EGR) Temperature Sensor “A” Circuit Range/Performance” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P040B

This diagnostic trouble code (DTC) is a generic code. Error P040B is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P040B – exhaust gas recirculation temperature sensor

EGR is responsible for exhaust gas recirculation. It is part of the vehicle’s exhaust emission system. It is used to reduce temperature, combustion pressure, and to control nitrogen oxides.

The function of the exhaust gas recirculation system temperature sensor is to control the temperature in the recirculation system. And regulate the flow accordingly with the exhaust gas recirculation valve. It is based on a conventional temperature-sensitive resistor-type sensor.

The OBD-II diagnostic tool can indicate P040B and related codes are active. When the ECM detects an out of range or functionality problem in the EGR temperature sensor circuit.

A problem with the exhaust gas recirculation temperature sensor is detected by the controller. This occurs when a performance range mismatch is detected in the Exhaust Gas Recirculation System Temperature Sensor “A” circuit.

Symptoms of vehicle malfunctions

The main signal that an error P040B has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be recorded in the ECM memory as a malfunction).
  2. Increased engine noise, and there may also be ringing and rattling.
  3. Increased emission of harmful substances in the exhaust.
  4. Excessive exhaust odor.
  5. There may be other symptoms as well.

Technically, error P040B is not considered serious, but in environmental terms, emissions are greatly increased. But it is necessary to correct the problem, because any malfunction can lead to more serious consequences.

Factors that can cause this error code

The error code P040B can mean that one or more of the following problems have occurred:

  • EGR temperature sensor is defective.
  • Leak in the EGR temperature sensor gasket.
  • Cracked or leaking exhaust pipe where the sensor is installed.
  • The wiring harness or sensor may be damaged.
  • Wires are open or shorted.
  • Damaged connector.
  • Intermittent communication with the control unit.
  • Sometimes faulty ECM module is the cause.

How to fix or reset OBD-2 code P040B

When fixing error code P040B, people quite often just replace the exhaust gas recirculation valve. But after that, they get that OBD error back again. The exhaust gas recirculation valve is not always the culprit.

Some suggested steps for troubleshooting and correction:

  1. Inspect the EGR as well as the sensor for damage.
  2. Clean the EGR valve as well as the tube to remove deposits.
  3. If you find a leak through the gasket, replace it.
  4. Check the continuity of the wires and connectors, and correct the problem if necessary.
  5. Test the ECM module and its communication.

Diagnose and repair of problems

First you need to read all saved data and error codes with the scanner. Then clear the error codes and test-drive the vehicle. To find out if error P040B appears again.

Then visually inspect the sensor and surrounding EGR system, look for exhaust leaks. Also check the sensor and the wiring harness that goes to it. High temperatures can cause damage to plastic and rubber insulated wires, so check them carefully.

Black soot may indicate an exhaust leak, so inspect the connections carefully.

Check the EGR sensor and system

Many exhaust gas recirculation problems are caused by soot buildup in the exhaust. Therefore, it may be helpful to clean the EGR system, or at least the temperature sensor.

After removing the sensor, use a carburetor cleaner or similar product to effectively soak up the soot. Use a metal brush to remove soot from excessively accumulated areas. When reinstalling a clean sensor, be sure to apply an anti-seize compound to the threads to prevent seizing.

Check the integrity of the sensor by measuring the actual electrical values against the manufacturer’s desired values. Do this with a multimeter and follow the manufacturer’s contact test procedures.

On which vehicles does this problem occur most frequently

Fault code P040B can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi (Q7)
  • Dodge (RAM)
  • Ford
  • Mazda
  • Mercedes-Benz (Sprinter)
  • Volkswagen (Touareg)

Fault code P040B can sometimes be found with other errors. The most common are the following: P040A, P040C, P040D, P040E, P040F.


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