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P02CA Turbocharger / Supercharger "B" Overboost Condition

OBD-II Trouble Code Technical Description

Article by
Don
Don Bowman
ASE Certified Automotive Tech

Turbocharger / Supercharger "B" Overboost Condition

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model.

Trouble code P02CA indicates the powertrain control module (PCM) senses a dangerously high boost pressure from the engine's "B" forced induction system. Levels of boost in excess of recommended levels can compromise the structural integrity of the engine. Refer to a vehicle specific repair manual to determine which is the "B" turbocharger or supercharger in your particular application.

Normally, an engine relies on the vacuum produced by the downward movement of the piston to draw the air and fuel charge into the engine. A supercharger or turbocharger is an air compressor used to increase the air and fuel charge entering the engine. This is known as "forced induction" which allows a much smaller fuel-efficient engine to create the power normally available with a much larger engine.

The mechanical apparatus used in forced induction is divided into three categories, positive displacement (roots style), centrifugal and turbo. The roots style and centrifugal chargers are belt driven while the turbo relies on pressure from the exhaust to operate.

A roots or positive displacement supercharger is positioned on the top of the intake. A centrifugal looks much like a rotary air conditioning compressor and is located on the driver's side front of the engine. Turbochargers are located in line with the exhaust system.

As boost pressure rises, the stress on the engine increases as well. Your engine has recommended boost pressure limits to preclude the possibility of engine component failure. Code P02CA is set when these limits are breached and should be corrected as soon as possible to prevent engine or transmission damage.

Turbo chargers rely on exhaust pressure to spin the turbine blades fast enough to produce air pressure greater than atmospheric. However they have an inherent lag where the exhaust pressure is insufficient to spin the turbo fast enough to create pressure. Depending on the type of unit used, the turbo needs 1700 to 2500 engine rpm before it begins to "spool up."

Turbos spin around 250,000 rpm in full boost. Boost pressure increases with engine rpm. To regulate the boost pressure and prevent overboost, a wastegate valve is installed. Most modern turbos have an internal wastegate and external actuator. There is a rod from the actuator to the wastegate on the turbo. Intake manifold air pressure passes to the top of the wastegate. As boost pressure increases it begins to exert force on the spring in the actuator that holds the wastegate valve closed. The higher the pressure rises, the more it overpowers the spring, resulting in the wastegate opening and directing exhaust gas away from the turbo blades and preventing further increase in boost.

Regulation of the pressure applied to the wastegate regulates the boost levels at specific rpm. To accomplish this, the computer uses barometric or MAP sensors, engine and transmission temperature sensors, knock sensors and intake pressure sensors to determine the amount of wastegate opening necessary to deliver the best boost levels.

To regulate boost levels, the computer uses either a solenoid, stepper motor or pulse modulator. By regulating the pressure to the wastegate actuator, varying degrees of boost are possible.

Symptoms

The symptoms displayed for a P02CA code will depend on the cause of the overboost condition:

Causes

Potential causes for this DTC include:

Diagnostic Steps & Possible Solutions

Inspect the wastegate actuator rod to the turbo. Repair it if its bent.

Inspect the hoses including the one from the boost controller to the wastegate actuator and the feed lines to the boost controller. Look for cracks or disconnected hoses. Pull the hose ends and look for plugged lines.

Connect a vacuum pump to the wastegate controller. Pump it slowly while watching the actuator rod. Make a note of the inches of mercury necessary to actuate the rod, or whether the rod moves at all. Consult a service manual for vacuum necessary to actuate the wastegate. If it is out of specification, replace the actuator.

If the rod fails to move or the wastegate actuator fails to hold vacuum, replace the actuator. If it holds a vacuum yet fails to move the rod, the internal wastegate in the turbo is stuck closed. Remove the turbo and have the wastegate repaired.

Start the engine and disconnect the supply hose to the boost controller. Inspect it for obstructions and boost pressure. Install the hose and disconnect the hose on the opposite side of the boost controller. There must be boost pressure present - if not replace the boost controller.

Related P02CA DTC Discussions

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