|Trouble Code||Fault Location||Probable Cause|
|P0028||Intake valve control solenoid circuit, bank 2 range/performance||Wiring, intake valve control solenoid|
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What Does Code P0028 Mean?
OBD II fault code P0028 is defined as “Intake Valve Control Solenoid Circuit Range/Performance (Bank 2)”, with “Bank 2” denoting the side of the engine opposite the cylinder #1 on engines with two cylinder heads. Code P0028 is set when the PCM (Powertrain Control Module) detects a fault in the electro-hydraulic control system of the VVT (Variable Valve Timing), or VCS (Variable Camshaft System).
The code setting parameter is generally a voltage variation that exceeds 10% of the reference voltage for the intake camshaft actuator for that particular application. Consult the relevant manual for the exact value of the voltage variation that will set code P0028 for the application being worked on.
VVT and VCS systems use pressurized engine oil to act on actuators that control variable valve timing. The PCM gathers information from various sensors regarding engine speed, engine load, throttle position, and others to calculate an appropriate valve timing setting to increase power, and/or improve fuel economy.
Since the engine oil is the agent that transfers power to the actuator that ultimately controls the intake valve timing, it should be obvious that oil of the correct type, viscosity, and cleanliness is crucially important to ensure the proper functioning of these systems. The image below shows a typical VVT control solenoid.
What are the common causes of code P0028 ?
The most common cause of code P0028 by a large margin is a low engine oil level, followed closely by low oil pressure issues and incorrect, or unsuitable lubricating oil. Other common causes of code P0028 include-
Open-, or short circuits in associated wiring.
Corroded electrical connectors.
Loss of ground contact.
Defective actuators, and/or control valves/mechanisms, although this is relatively rare.
Failed, or failing PCM, which is even more rare, but not altogether impossible.
What are the symptoms of code P0028 ?
Although the symptoms of code P0028 are much the same on all vehicles, the severity of one or more symptoms may vary from vehicle to vehicle. Below are some common symptoms of this code-
Illuminated check engine light.
Significantly reduced engine power at some engine speeds.
In some cases, engine misfiring may be present at some engine speeds.
Increased fuel consumption.
Hard starting when jammed/damaged actuators do not allow valve timing to return to base settings. Note that in these cases, other codes that are closely related to P0028 might be present.
How do you troubleshoot code P0028 ?
NOTE: When diagnosing code P0028, start the procedure by inspecting the engine for oil leaks that could have reduced the engine oil level. Repair oil leaks as required, top off the oil level, clear the code, and operate the vehicle. Rescan to see if the code returns. If the code persists, proceed as follows-
Check the engine oil level, and adjust the level to the correct mark. Clear the code and operate the vehicle to see if the code returns.
NOTE: At this point, it is important to determine if the engine is filled with suitable oil. For instance, mineral oil in an engine that requires synthetic oil can cause the formation of sludge, gums, and varnishes that can interfere with the correct operation of actuators and control valves/mechanisms. Replace the oil and filter if there is any doubt about the type, grade, viscosity, or age of the engine oil.
If the engine oil is at the correct level, and of the correct type and grade, perform an oil pressure test to verify that the oil pressure is within specification. Low oil pressure is major cause of code P0028. If the oil pressure does not conform to specification, locate and repair the cause before commencing with the diagnostic procedure.
If the oil pressure is within specification, perform a thorough inspection of all related wiring and connectors. Repair all defects as required, but be sure to check the circuit for reference voltage, continuity, and ground contact. Be sure however to disconnect all control modules before commencing continuity checks. Consult the relevant manual to determine the color-coding, location, and function of each wire in the connector, as well as the exact values of the reference voltage.
If repairs to the wiring/connectors were made, clear the code, operate the vehicle, and rescan to see if the code is still present. If the code persists, there may be an intermittent fault present, and you may have to allow it to worsen before an accurate diagnosis can be made.
If no faults are found during the inspection and testing of the electrical circuit, remove the actuators and control valve(s)/mechanism(s), and inspect them for evidence of damage, or the presence of sludge that could interfere with their operation. Clean all components as required, and test their operation before re-installing them.
NOTE: With some scanners and code readers, it is possible to operate the actuators or control valves manually. Where this is not possible, consult the relevant manual on the correct testing procedures, but be sure to follow the directions exactly to ensure a valid diagnosis.
If the actuator or control valve/mechanism works when it is operated manually, it is likely that internal oil passages in the engine may be blocked. Reinstall all components, and perform an engine flush with a suitable agent to dissolve any possible sludge or blockage(s) in the VVT or VCS oil supply circuit.
Change the oil and filter to remove the engine flush agent, clear all codes, and operate the vehicle to see if the code returns. It is very unlikely to happen at this point, but not impossible, so if the code persists after an engine flush, replace the actuator or control valve/mechanism, and retest the vehicle. If despite all previous repair attempts the fault persists, there are three possibilities to consider.
One is that the blockage in the oil supply circuit is not fully cleared, and the other is an intermittent fault that could be extremely challenging to find and resolve, which means that the fault may have to be allowed to worsen considerably before an accurate diagnosis and definitive repair could be made.
One other, albeit unlikely, possibility involves a possible defective PCM, but PCM failures are exceedingly rare, meaning that all other avenues must be explored to trace and correct the root cause of code P0028 before the PCM is replaced.
Codes Related to P0028
P0026 – Relates to Intake Valve Control Solenoid Circuit Range/Performance (Bank 1), with “Bank 1” denoting the side of the engine that includes cylinder #1.