What the P3478 code means
When starting your vehicle, and when the vehicle is operating under a heavy weight, the engine will work in V8 mode. But when driving conditions are light, the engine will disable 4 of the 8 cylinders, thereby changing from V8 to V4 mode. Using information it receives from the mass airflow sensor, your vehicle will determine the proper driving conditions.
The PCM will then instruct the cylinder deactivation solenoids and this will begin what is known as the cylinder deactivation process. The cylinder deactivation solenoids will deactivate cylinder 1, cylinder 4, cylinder 6, and cylinder 7, and it does this by restricting the flow of oil to the valve lifters for these cylinders, and then stopping your intake valves and exhaust valves from opening.
When the PCM detects that the measured values of the mass airflow sensor, the intake control manifold absolute pressure sensor, and the throttle position sensor are no longer within the range of V4 mode, this is when it will store the P3478 diagnostic trouble code.
What causes the P3478 code?
There may be one or more causes for the P3478 code:
Defective throttle position sensor
Low oil level in your engine
Poor oil pressure on the lifters
Clogged or restricted oil passages
Defective cylinder deactivation solenoid
Defective intake control manifold absolute pressure sensor
Defective mass airflow sensor
An open or short in the cylinder deactivation solenoid harness
A poor electrical connection in the cylinder deactivation solenoid circuit
What are the symptoms of the P3478 code?
Some symptoms include a Check Engine light that will not turn off and a vibrating engine.
How does a mechanic diagnose the P3478 code?
The first thing you want to do is make sure that your engine’s oil pressure and oil levels are correct. Make sure to use your OBD-II scanner to collect all diagnostic trouble codes stored by the powertrain control module (PCM). Remember that if the powertrain control module (PCM) has stored other deactivation or oil pressure trouble codes, these should be dealt with first. Always attend to the codes in the order they appear.
Next clear the trouble codes with your OBD-II scanner, and then test the cylinder deactivation solenoid #1 by actuating the cylinder with a scan tool. A solenoid that is in good working order will vibrate and make a small clicking noise. If the cylinder deactivation solenoid #1 is working incorrectly or not at all, examine your oil passages for debris and clean those passages if you feel they should be cleaned. Afterward, replace the solenoid.
Common mistakes when diagnosing the P3478 code
One common mistake is not checking the oil passageways for buildup and sludge. Clogged oil passageways can decrease engine oil pressure and thereby prevent the cylinder deactivation solenoids and lifters from operating as they should. Always be sure to examine the oil passageways to make sure that you are properly diagnosing the problem.
How serious is the P3478 code?
Not attending to this problem could cause an increase in engine emissions and a loss of fuel economy. Although a P3478 code is not as serious as some others, you should attend to it quickly, as over time it could produce irreversible effects and damage other components.
What repairs can fix the P3478 code?
Several repairs can be done for a P3478 code. Of course it depends on the exact issue that your vehicle is having. One thing you might do is repair or replace your cylinder deactivation solenoid #1.
You might also repair or replace your cylinder deactivation solenoid #7 or clear your cylinder deactivation solenoid oil passages of buildup and debris. Another option is to replace the lifters in your engine. If your entire engine is clogged with sludge and dirt, you probably need to disassemble the engine and clean it thoroughly.
Additional comments for consideration regarding the P3478 code
This code can become complicated and may require that you disassemble the entire engine to fix the problem correctly. Obviously, this may become a complicated and involved task even for the most experienced technician. Therefore, it is important to do the proper amount of research before you take your engine apart. Do not hesitate to contact a professional technician to ask questions about your problem.
Need help with a P3478 code?
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