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P046F Exhaust Gas Recirculation Sensor B Circuit Intermittent

OBD-II Trouble Code Technical Description

Article by
Don Bowman
ASE Certified Automotive Tech

Exhaust Gas Recirculation Sensor "B" Circuit Intermittent/Erratic

What does that mean?

This is a generic powertrain diagnostic trouble code (DTC), which means it covers all makes/models, 1996-newer. However, specific troubleshooting steps will vary depending on the vehicle.

On board diagnostics (OBD) trouble code P046F is a generic trouble code relating to an intermittent or erratic problem incurred in the "B" electrical circuit to the exhaust gas recirculation (EGR) valve.

The purpose of the EGR valve is to introduce a regulated amount of exhaust gas into the intake manifold. The purpose is to maintain cylinder head temperatures below 2500-degrees F. Nitrates of Oxygen (Nox) form when temperatures rise above 2500-degrees F. Nox is responsible for smog and atmospheric pollution.

The controlling computer, either the powertrain control module (PCM) or the electronic control module (ECM) has detected an abnormally low, high or non-existent signal voltage. Refer to a manufacturer specific repair guide to determine which is the "B" sensor in your exact vehicle.

EGR Operating Principals

The trouble code P046F refers to the same problem on all vehicles, however, there are many types of EGRs, sensors and methods of activation. The only similarity is that they all vent exhaust gas into the intake manifold to cool the cylinder head temperatures.

Introducing spent exhaust gas into the engine at the wrong time reduces horsepower and causes a rough idle or stall. With this in mind, computer programming only opens the EGR when the engine RPM is above 2000 and to close when under a load.


The symptoms depend on the position of the EGR pintle at the time of failure.

Potential Causes

Repair Procedures

All EGR valves have one thing in common-they re-circulate exhaust from the exhaust to the intake manifold. Other than that, they differ in their methods for regulating the opening of the pintle and sensing its position.

The following repair procedures represent the most common problems accounting for the majority of failures in the EGR system. Wiring harness or sensor failures require a service manual to determine the proper wire identification and diagnostic procedures.

Keep in mind that the wiring differs between manufacturers and computers do not react well if the wrong wire is probed. If you probe the wrong wire and send excessive voltage through the computer's sensor input terminal and the computer will fry.

At the same time, if the wrong connector is disconnected the computer could lose its programming causing the vehicle to fail to start again until the dealer reprograms the computer.

If the most common tests failed to solve the problem, a service manual is needed to continue to test the wiring circuits. The best solution is to take the vehicle to a service facility with the proper diagnostic equipment. They can quickly identify and repair this type of problem.

Related P046F DTC Discussions

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