What does it mean?
This DTC is a generic powertrain code that applies to all turbocharged or supercharged vehicles.
The Powertrain Control Module (PCM) controls and monitors both the boost pressure and if the measured pressure is higher than the commanded pressure, DTC P0240 will be set and the PCM will illuminate the Check Engine light. To diagnose this code, you need to have a general understanding of three things:
What is boost pressure?
How is it controlled?
How is it measured?
In a normally aspirated engine (i.e., non-turbo), the downward movement of the pistons, called the intake stroke, creates a vacuum in the intake manifold in the same way a syringe draws in liquid. This vacuum is how the air/fuel mixture is drawn into the combustion chamber. A turbocharger is a pump driven by exhaust gases as they exit the combustion chamber. This creates pressure in the intake manifold. So, instead of the engine having to “suck” in the air/fuel mixture, it is instead force-fed a larger volume. In essence, there is already compression before the piston begins its compression stroke, which increases compression and thus increases power. This is boost pressure.
Boost pressure is controlled by the amount of exhaust gas allowed to pass through the turbo. The higher the amount, the faster the turbo spins, the higher the boost pressure. Exhaust gases are routed around the turbo via a bypass known as a wastegate. The PCM controls the boost pressure by regulating the opening of the bypass. It does this by opening or closing the wastegate as needed. This is accomplished by means of a vacuum motor mounted on or near the turbo. The PCM controls the amount of vacuum going to the vacuum motor via a control solenoid.
The actual pressure in the intake manifold is measured either by a boost pressure sensor (Ford/VW) or a manifold absolute pressure sensor (Chrysler/GM). The different sensor types represent the different technical description given by each manufacturer, but both perform the same function.
This particular code should be addressed as soon as possible due to the increased risk of overboost and damage to the catalyst.
Symptoms
When the conditions for setting P0240 are present, the PCM ignores the actual manifold pressure readings and uses an assumed or presumed manifold pressure, limits the amount of fuel and dynamic injection timing allowed. The PCM enters what is called Failure Mode Engine Management (FMEM) and is most noticeably characterized by a lack of power.
Causes
Causes
possible causes for setting this code are as follows:
Vacuum supply
Pinched, collapsed, or broken vacuum lines
Faulty control solenoid
Faulty PCM
Diagnostic and Repair Procedures
A good starting point is always to check the Technical Service Bulletins (TSBs) for your particular vehicle. Your problem may be a known issue with a known fix published by the manufacturer and can save you time and money when diagnosing.
Visually inspect vacuum lines for kinks, pinches, cracks, or breaks. Check all lines, not just those related to “B” wastegate control. A significant leak anywhere in the vacuum system can lead to poor performance of the entire system. If this checks out, proceed to step 2.
Using a vacuum gauge, check the vacuum on the inlet side of the “B” control solenoid. If none is present, suspect a faulty vacuum pump. If vacuum is present, proceed to step 3.
The control solenoid is actuated by pulse width modulation or duty cycle. Using a digital volt ohmmeter, which has a duty cycle or frequency setting, probe the signal wire at the solenoid connector. Drive the vehicle and check that a signal appears on the DVOM. If the signal is present, suspect a faulty control solenoid. If no signal is present, suspect a faulty PCM.