Error Code P0471 is defined as Exhaust Pressure Sensor Range/Performance. This means the PCM has detected a voltage that is out of the normal range, a problem caused by exhaust back pressure system.

This trouble code is a generic error code, which means it applies to all vehicles with variable nozzle turbochargers (diesel or gas), or vehicles made since 2006 on Ford trucks equipped with 6L diesel engines, Ford EcoBoost engines and the Cummins 6.7L in 2007, the 3.0L in the Mercedes lineup in 2007 and here recently the Cummins 3.0L 6 cyl in the Nissan pickups starting in 2015. That’s not to say you wouldn’t necessarily get this code in a VW or other make though.

Definition

Error Code P0471 takes place when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a voltage reading a voltage reading that is out of the normal range for the exhaust system back pressure sensor circuit. This code happen when the incoming signal from the exhaust pressure sensor not matching the pressure from the intake manifold or ambient pressure at key on. This can be caused by a fault in the electrical circuit or a mechanical failure. This usually happens in vehicles that turbocharged and diesel engines.

Error Code P0470 can also be present, and P0470 and P0471 are actually related codes. The only difference between the two is the length of time the problem lasts, as well as the type of electrical or mechanical problem that the sensor, circuit or engine controller is having. Troubleshooting can vary from one manufacturer to another, type of engine (gas or diesel), exhaust pressure sensor types and wire colors.

Common Symptoms

As with other trouble codes, P0471 triggers the Check Engine light. Other symptoms include:

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  • Lack of power from the engine
  • Unable to perform manual regeneration
  • This problem can lead to crank-no-start condition

Possible Causes

There are a number of things that could cause Error Code P0471, including the following:

  • Faulty exhaust back pressure sensor
  • Shorted or open exhaust back pressure sensor
  • Poor electrical connection with exhaust back pressure sensor circuit
  • Blocked or clogged tube that runs from pressure sensor to the exhaust manifold
  • Leaks in the exhaust gas recirculation system, air inlet or charge air leaks
  • Failed PCM (rare, but possible)

How to Check

As with other trouble codes, mechanics start their diagnosis for Error Code P0471 by connecting an OBD-II scanner to the onboard computer of the vehicle. This is to gather stored data that will tell the mechanic the different codes stored in the vehicle’s computer, and give him a better idea on how to advance in diagnosis and conduct repair.

The codes are then reset and the vehicle will be taken to test drive to see if the error codes come back. If they do come back, then that means there’s an actual problem.

Then they proceed by checking the exhaust back pressure sensor. They disconnect the tube that connects the exhaust manifold to the exhaust pressure sensor and try to run air through it. If that step proves to be impossible, they will dislodge whatever is causing the blockage using a wire.

Next, mechanics will check the wiring involved, and look for signs of damage. The connectors will also be checked thoroughly. If the problem requires cleaning the terminals, use an Electrical Contact cleaner (available from any parts store) to clean the terminals. They use a cleaner with 91% rubbing alcohol and a light plastic bristle brush. They let the terminals dry, and then they get a dielectric silicone compound (same stuff you use for spark plug wires and light bulb) and put some where the terminals come into contact. They make sure there are no leakages to the tubes that connect to the turbocharger. Then, they inspect the tube connections around the turbocharger and intake manifold; tighten all hose and band clamps.

To test the power supply circuit and make sure it’s working properly, the harness that runs to the exhaust pressure sensor can also be disconnected.

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If nothing seems to work, then the problem is most likely caused by a malfunctioning exhaust pressure sensor. Although failed PCM should also not be ruled out, until the sensor had been replaced.

How to Fix

The fix for this error code obviously, depends on the results of the diagnosis. But some of the most common repairs are:

  • Repair or replace damaged wiring or connectors that are shorted or corroded
  • Repair or replace exhaust pressure sensor
  • Unclog the tubes that connects the exhaust pressure sensor to the exhaust manifold, and make sure they’re clear

One of the most common misdiagnosis for this error code is that, people assume it’s an exhaust gas recirculation code. Thus, it is important to conduct a thorough diagnosis to find the right repairs necessary.