What does it mean?
This DTC is a generic powertrain code that applies to all turbocharged vehicles. The differences in the descriptions above are due to the method of measuring pressure in the intake manifold.
The Powertrain Control Module (PCM) controls and monitors both the boost pressure and whether the measured pressure is higher than the commanded pressure. If it is, the DTC P0236 will be set, and the PCM will illuminate the check engine light. To diagnose this code, you need a general understanding of three things:
What is boost pressure?
How is it measured?
In a naturally aspirated engine (i.e., non-turbo), the downward movement of the pistons, called the intake stroke, creates a vacuum in the intake manifold, similar to how 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 force-fed a larger volume. Essentially, compression is already happening before the piston begins its compression stroke, which increases compression and thus boosts power. This is boost pressure.
How is it controlled?
Boost pressure is controlled by the amount of exhaust gas allowed to pass through the turbo. The more exhaust gas, the faster the turbo spins, and the higher the boost pressure. Exhaust gases are routed around the turbo via a bypass known as the 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 achieved using 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 types of sensors represent the varying technical descriptions given by each manufacturer, but both serve the same function.
This particular code should be addressed as soon as possible due to the increased risk of overboost and damage to the catalytic converter.
Symptoms
When the conditions for setting P0236 are present, the PCM ignores the actual manifold pressure readings and uses an assumed or estimated manifold pressure, limiting the amount of fuel and dynamic injection timing allowed. The PCM enters what is called Failure Mode Engine Management (FMEM), which is most noticeable as a lack of power.
Possible causes for this code being set include:
- 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 specific vehicle. Your issue may be a known problem with a published fix from the manufacturer, which can save you time and money during diagnosis.
Visually inspect the vacuum lines for twists, pinches, cracks, or breaks. Check all lines, not just those related to wastegate control. A significant leak anywhere in the vacuum system can lead to poor performance of the entire system. If everything looks good, proceed to step 2.
Using a vacuum gauge, check the vacuum on the input side of the control solenoid. If there is none, suspect a faulty vacuum pump. If vacuum is present, proceed to step 3.
The control solenoid is operated by pulse width modulation or duty cycle. Using a digital volt-ohmmeter (DVOM) with a duty cycle or frequency setting, probe the signal wire at the solenoid connector. Drive the vehicle and check if a signal appears on the DVOM. If a signal is present, suspect a faulty control solenoid. If no signal is present, suspect a faulty PCM.