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Error Code P0474 is defined as Exhaust Pressure Sensor Circuit A Intermittent. This means there could be a clogged back tube or problem with the exhaust back pressure regulator, causing an abnormal voltage reading.
This code is a generic trouble code, meaning it applies to all vehicles equipped with variable nozzle turbochargers (both gasoline and diesel engines). This started around 2005 on Ford trucks equipped with 6.0L diesel engines, all Ford EcoBoost engines, and eventually to Cummins 6.7L in 2007; Mercedes lineup with 3.0L engines in 2007 and the Cummins 3.0L 6 cyl in Nissan pickups starting in 2015. This code also applies to some VW vehicles models.
Error Code P0474 is stored when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) determines that the voltage reading from the exhaust system back pressure is too low or too high.
To control the exhaust back pressure regulator in diesel or turbocharged engine, the exhaust back pressure sensor supplies a voltage reading to the PCM that indicates the current pressure level. If this voltage doesn’t match the specifications set by the manufacturer, the PCM will store the error code P0474.
Other related codes include:
- Error Code P0470 Exhaust Pressure Sensor “A” Circuit
- Error Code P0471 Exhaust Pressure Sensor “A” Circuit Range/Performance
- Error Code P0472 Exhaust Pressure Sensor “A” Circuit Low
- Error Code P0473 Exhaust Pressure Sensor “A” Circuit High
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Engine lacks power
- Manual regeneration will be impossible
- Eventually, the problem can lead to crank-no start as well
- A crank-no start (if a perform regeneration isn’t able to perform)
Clogged pressure sensor and defective exhaust pressure sensor are the two most common causes of this code. Other causes include:
- Damaged connectors or wirings
- Shorted or open exhaust back pressure sensor harness
- Defective PCM
How to Check
As with most error codes, mechanics start their diagnosis by verifying the code using an OBD-II scanner.
Next, they will inspect all the components, including connectors, wirings, and other components related to the exhaust backpressure system. Any damaged, faulty, and loose connectors must be fixed (repair or replaced).
Then, mechanics will clear the code from the system and retest the system to see if the code comes back.
If the code comes back, that means the mechanic has successfully diagnosed the problem with the exhaust back pressure system, and can now move on to the repairs.
How to Fix
Mechanics start their repair by inspecting the electrical components of the associated components of the vehicle at fault. Once the diagnostic step has been performed, and the issues revealed to be unrelated, other repairs must be employed. Common repairs include:
- Clearing and replacement of clogged back pressure tube
- Cleaning or replacement of defective exhaust back pressure sensor
- Repair or replacement of shorted or open exhaust back pressure sensor harness
- Manual test of individual circuits within the exhaust back pressure system and replacement of the defective components
- Replacement of PCM (rare)
As with other repairs for other codes, it is important to code is cleared from the system, and the system is retested after each step of the repair. This helps narrow down to the exact cause of the problem.
Though Error Code P0474 is a minor issue, and the underlying problem that’s causing it will not result to drivability problems, it may keep the vehicle from passing emission test until the code is repaired and cleared.