Fault code P0234 is called “Turbocharger/Supercharger “A” Overboost Condition” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0234
This Diagnostic Trouble Code (DTC) is a generic powertrain code. Error P0234 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.
Fault code P0234 indicates that the Powertrain Control Module (PCM) has detected dangerously high supercharging pressure from the engine forced intake system. Supercharging levels in excess of the recommended levels can compromise the structural integrity of the engine.
The engine normally relies on the vacuum created by the downward movement of the piston to draw air and fuel into the engine. A supercharger or turbocharger is an air compressor used to increase the amount of air and fuel going into the engine. Which allows a smaller engine to create power normally available to a much larger engine.
As the supercharger pressure increases, the load on the engine also increases. There are recommended boost pressure limits for the engine. To eliminate the possibility of engine component failure. Code P0234 is set when these limits are violated, must be corrected as soon as possible. To prevent damage to the engine or transmission.
Turbocharger operation
Turbochargers rely on exhaust pressure to spin the turbine blades fast enough to create air pressure above atmospheric pressure. But they do have a lag when the exhaust pressure isn’t enough. Depending on the type of unit used, a turbine engine needs between 1,700 and 2,500 rpm before it begins to “spin out.”
Turbines at full power rotate at about 250,000 rpm. The boost pressure increases as the engine speed increases. A bypass valve is installed to regulate this pressure and prevent overcharging.
Most modern turbines have an internal bypass valve and an external actuator. The turbocharger has a stem from the actuator to the bypass valve. The air pressure in the intake manifold travels to the top of the bypass damper.
As the boost pressure increases, it begins to exert a force on the spring in the actuator. Which holds the bypass valve closed. The higher the pressure increases, the more it presses on the spring. This causes the bypass valve to open and directs the exhaust gases away from the turbocharger blades. This prevents a further increase in boost.
Adjusting the pressure applied to the bypass damper adjusts the boost levels at specific RPMs. The computer uses barometric or MAP sensors to do this.
It also uses sensors for engine and transmission temperature, detonation, and intake pressure. This is done in order to determine the amount of bypass damper opening required to provide the best boost level.
The computer uses a solenoid, stepper motor or pulse modulator to adjust the boost levels. By adjusting the pressure on the bypass damper actuator, different boost levels can be obtained.
Symptoms of vehicle malfunctions
The main signal that an error P0234 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up.
- Loss of power may be observed.
- Engine overheating with subsequent problems.
- The transmission may also show signs of overheating and abrupt shifting.
- Additional codes associated with an established P0234 error can help determine the cause. Codes are available for all electrical components used by the engine control computer to control boost levels.
- Premature ignition, resulting in noticeable detonation.
- Ignition jerking/missing.
Increasing the boost pressure increases engine power, but overpressure can have catastrophic consequences. The most common are a cylinder-head gasket burst or damage to the cylinder block itself. Therefore, it is recommended that P0234 is repaired as soon as possible.
Factors that can cause this error code
The error code P0234 can mean that one or more of the following problems have occurred:
- Faulty MAP sensor (absolute manifold pressure).
- Damaged, burned, shorted, disconnected, or corroded wires and/or connectors in MAP sensor control circuit.
- Damaged, broken, cracked or displaced vacuum tubes.
- Malfunction of the turbine control lamp.
- Mechanical failure of turbine control valve N75.
- Blocked turbine variable geometry mechanism. This is more common in vehicles that spend long periods of time in storage or in vehicles that are not used regularly.
- Self-modification of the exhaust system.
- The bypass damper is stuck in the closed position, causing the turbocharger to spin higher than normal, resulting in excessive acceleration.
- The stem from the actuator on the turbocharger is bent.
- The hose from the supercharger regulator has torn off.
- The supply to the supercharger controller or from the controller to the bypass damper is clogged.
- Dodge trucks with a Cummins diesel engine have a particular problem. They are running properly. But the check engine light comes on and code P0234 is displayed at idle. However, the indicator goes out after a few minutes at cruising speed. The digital boost control gauge is connected to the MAP sensor. Which occasionally fails at idle, but does not set the code. Replacing the MAP sensor fixes this.
How to fix or reset OBD-2 code P0234
Some suggested steps for troubleshooting and fix the error code P0234:
- Check the electrical circuits as well as the MAP sensor.
- Inspection of vacuum tubes.
- Determination of mechanical faults of the turbine (stem, flap, valve).
- Check hoses for clogging or other impurities.
Diagnose and repair of problems
Inspect the bypass damper actuator rod on the turbocharger. Repair it if it is bent.
Inspect the hoses, including the hoses from the charge controller to the bypass damper actuator and the supply lines to the charge controller. Look for cracks or disconnected hoses. Inspect the hose ends for blockages.
Connect the vacuum pump to the bypass valve controller. Pump it slowly while observing the actuator stem. Note the amount of mercury column required to actuate the rod and whether the rod is moving at all.
Refer to the service manual regarding the vacuum required to actuate the bypass damper. If it is out of specification, replace the actuator.
If the rod does not move or the bypass damper actuator cannot hold a vacuum, replace the actuator. If it holds vacuum but cannot move the stem, the internal bypass valve in the turbocharger is jammed. Remove the turbocharger and repair the bypass valve.
Start the engine and disconnect the supply hose from the charge regulator. Inspect it for obstructions and boost pressure. Install the hose and disconnect the hose on the opposite side from the boost regulator. There must be boost pressure present – if not, replace the charge controller.
On which vehicles does this problem occur most frequently
Fault code P0234 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Acura (RDX)
- Audi (A3, A4, A6, Q7)
- Chevrolet (Captiva)
- Chrysler
- Citroen (Jumper)
- Dodge (Journey)
- Fiat (Doblo)
- Ford (C-Max, Escape, Focus, Kuga, Mondeo, S-Max, Transit)
- Hyundai (Santa Fe, Starex)
- Iveco (Daily)
- Jeep (Grand Cherokee)
- Kia (Sorento)
- Land Rover (Freelander)
- Mercedes-Benz (Sprinter)
- Mitsubishi (L200, Pajero)
- Nissan (Juke, Navara, Pathfinder)
- Opel (Astra, Corsa, Insignia, Mokka, Vectra, Zafira)
- Peugeot (Boxer)
- Porsche (Cayenne)
- Renault (Duster, Megane)
- Saab
- Skoda (Octavia)
- Toyota
- Volkswagen (Caddy, Crafter, Golf, Jetta, Multivan, Passat, Tiguan, Touareg, Touran)
- Volvo (S60, XC90)
- GAZelle (Next)
Fault code P0234 can sometimes be found with other errors. The most common are the following: P007D, P0095, P0236, P0238, P0299, P0380, P0453, P1103, P26B7.
