P0479 code definition
If the PCM has stored the P0479 code, it means that there has been an out-of-the-ordinary voltage reading from the exhaust pressure control valve circuit. This code is primarily seen in diesel and turbocharged gasoline engines, where exhaust pressure is typically monitored.
What the P0479 code means
In a diesel or turbocharged gasoline engine, the exhaust back pressure valve is responsible for controlling the exhaust pressure. Based on data from the throttle position sensor, tachometer, and other sensors, the PCM will automatically calculate the desired exhaust back pressure based on manufacturer recommendations. If the variable resistant circuit that supplies data regarding the exhaust back pressure valve’s voltage reports a voltage that is higher or lower than the desired pressure, the PCM will store the OBD-II generic code P0479.
What causes the P0479 code?
Typically, this code is caused by a back pressure tube or an exhaust back pressure sensor that is clogged, or by leaks in the exhaust system.
Other causes may include:
- Damaged or burnt out electrical wiring
- Damaged connectors
- Open circuits between the exhaust pressure sensor and the PCM
- Turbocharger overboost
- In rare cases, a faulty PCM
What are the symptoms of the P0479 code?
If the P0479 is detected, it is likely that the engine performance has been suffering. Insufficient turbocharger pressure will have reduced the engine performance, and the exhaust back pressure regulator may be automatically disabled if the PCM stores this code. The regulator can be disabled in the open position or the closed position depending on the model. Finally, the Check Engine Light will be lit.
How does a mechanic diagnose the P0479 code?
If the P0479 code is detected by the OBD-II scanner, a technician should begin with a visual inspection of all the wiring, connectors, and other components of the exhaust pressure control system. After repairing these issues and clearing the code, the technician should take the vehicle for a test drive, and see if the Check Engine Light returns. If it does, they should begin pursuing other repair options.
Common mistakes when diagnosing the P0479 code
When diagnosing the P0479 code, it is common to confuse it with the code for the exhaust gas recirculation. These two valves are located near each other on many cars, but both codes are diagnosed and repaired differently.
How serious is the P0479 code?
Because this P0479 code directly relates to the performance of the engine, it represents a serious repair that should be addressed as soon as possible. Not addressing this repair may cause the vehicle’s gas mileage to suffer, and it is likely that the vehicle would not pass an emissions test while this code is stored in the PCM.
What repairs can fix the P0479 code?
When the P0479 code has been detected with an OBD-II scanner, the technician should begin a thorough diagnosis that may include the following actions:
- Perform a visual inspection of all wiring and connectors, and repair any that appear damaged.
- Clear the code from the PCM, and take the vehicle for a test drive to determine if the Check Engine Light returns.
- Obtain the back pressure to voltage conversion data, as well as the back pressure system schematics, for the vehicle make and model. Perform a manual check of the back pressure voltage with a digital volt/ohmmeter and compare findings with the manufacturer’s specifications.
- Remove and clean the exhaust back pressure tube and sensor.
- Repair or replace other open or shorted wiring or connectors of all circuits.
- Replace the solenoid.
After each of these possible repairs, the technician should clear the code and check the PCM again; if the code continues to return, the issue may be an intermittent one. If these repairs do not solve the issue, it may be time to suspect a faulty PCM.
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