P0474 code definition
The P0474 code is stored when the PCM calculates that the voltage reading from the exhaust system back pressure sensor circuit is too low or too high.
What the P0474 code means
In order to control the exhaust back pressure regulator in a diesel or turbocharged engine, the exhaust back pressure sensor supplies a voltage reading to the ECM that indicates the current pressure level. If this data does not match the manufacturer’s specifications, the PCM will store the P0474 code.
What causes the P0474 code?
A clogged back pressure tube, or a faulty exhaust back pressure sensor, are the two most likely causes for the P0474 code to be stored. However, other common causes may include:
- Damaged electrical wiring and connectors
- Shorted or open exhaust back pressure sensor harness
- Faulty PCM, in very rare cases
What are the symptoms of the P0474 code?
In many cases, the exhaust back pressure regulator will be disabled, in either a closed or open position, when the P0474 code is stored. This may cause reduced engine performance and insufficient turbocharger pressure. The Check Engine Light will be illuminated, and there may be other codes stored in the PCM relating to the turbocharger or the exhaust systems.
How does a mechanic diagnose the P0474 code?
In order to diagnose the P0474 code, a mechanic should first verify the code with an ODB-II scanner. They should then inspect all the electrical components, including wiring and connectors, related to the exhaust back pressure system, and replace or repair any that are damaged, loose, or faulty. After clearing the code from the system, the mechanic should retest the system. If the code returns, the mechanic has successfully diagnosed an issue with the exhaust back pressure system, and can move on to other repairs.
Common mistakes when diagnosing the P0474 code
When diagnosing the underlying cause of the P0474 code, it is common to confuse the issue with a malfunction in the exhaust gas recirculation. The exhaust back pressure tube and the exhaust gas recirculation valve are located in the same area, but both are diagnosed and repaired in different manners.
How serious is the P0474 code?
The P0474 code is an intermediate issue. While the underlying problem causing this code isn’t likely to affect drivability, it may mean that the vehicle will not pass an emissions test until the issue is repaired and the code is cleared.
What repairs can fix the P0474 code?
In order to repair the underlying issue causing the P0474 code, the mechanic will begin with the initial inspection and repair of the electrical components. Once this diagnostic step has been performed, and the issue is revealed to be unrelated, there are other repairs that may be attempted. They include:
- Clearing or replacing a clogged back pressure tube.
- Replacing or cleaning a faulty exhaust back pressure sensor.
- Replacing or repairing a shorted or open exhaust back pressure sensor harness.
- Manually test individual circuits within the exhaust back pressure system, and replace faulty components.
- In rare cases, replacing a faulty PCM.
It is important that after each repair is attempted, the code is cleared from the system and the system is retested. This process helps narrow down the underlying cause of the code so that it is not stored again after a repair.
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