Hyundai Theta Engine Problems - Turbocharged Systems

Solving Hyundai Theta Engine Problems

Knowing the basics of turbocharged systems can serve you well in solving problems with turbo-equipped Hyundais.

Hyundai has two four-cylinder engines that use a turbocharger. The Gamma and Theta turbocharged engines were introduced in 2010 for many Hyundai cars and trucks. These engines also have direct injection, which makes them even more efficient.

Knowing the basics of how all turbocharged systems work can serve you well in solving problems with turbo-equipped Hyundais. A good scan tool that can graph boost pressure and a smoke machine can also improve your diagnostic procedures.

Oil Quality

The key to keeping the turbo (and, more importantly, the timing chain) healthy is the quality of oil and the frequency of oil changes. Since 2011, the owner’s manual has specified an ILSAC GF-4 oil with an API SM rating. But, there have been upgrades. ILACS GF-5 oils are available and API has issued SN and SN-Plus oils that can extend the life of the turbocharger, timing chain and even the high-pressure fuel pump.

Hyundai recommends changing the oil and filter between 3,000 to 5,000 miles, depending on how the vehicle is driven. Not changing the oil will cause the oil to form deposits in the turbocharger’s housing. These deposits will cause restrictions in the oil passages and the turbocharger to run hotter.

WGT Operation

The wastegate manages the flow of exhaust gases over the turbine. If the boost reaches a specific level, the gate opens and exhaust gases bypass the turbine. Depending on the engine, Hyundai can actuate the wastegate with a vacuum pressure pot or stepper motor. Both actuation methods have adjustment procedures.

The first-generation Gamma 1.6 turbocharged engine uses a pressure-actuated wastegate. A diaphragm working against a spring controls the wastegate. Vacuum pressure inside the actuator is controlled by a solenoid that receives a pulse-width modulated signal that is controlled by the ECM.

The Wastegate Solenoid Valve Control Solenoid Valve (WGT) controls the actuator that opens the bypass passage of the turbocharger turbine. In order to drop the turbine internal pressure, the ECM restricts the turbine rotation by opening the bypass passage.

There are alignment marks on the arm of the wastegate and housing. Lengthening and shortening the rod adjusts the wastegate. The actuator rod should move when a vacuum of -9.08 psi is applied to the actuator.

The 2.0 L GDI turbocharged Theta engine uses a stepper motor to open the wastegate. The Electric WGT (EWGAT) is installed on the turbocharger. The actuator consists of a DC motor that actuates the wastegate. Inside the unit is a two-step gear transmission that increases the torque of the motor.

The EWGAT has a position sensor that measures the voltage from the open stop to the closed stop. The voltage from the sensor is used to measure the position of the vane. The five-volt signal correlates with the amount of wastegate lift. The sensor output on a scan tool is used to adjust the rod. The adaption mode menu for the EWGAT needs to be activated. The target voltage is listed in the service information and can vary, depending on the model and year. Turning the rod end clockwise will increase the voltage; turning it counterclockwise will decrease the voltage.

Recirculation Valve Control (RVC)

Hyundai calls its blow-off or diverter valve a Recirculation Valve Control (RVC). An electronic solenoid valve that controls engine vacuum operates the RVC. The valve recirculates air back into the intake or air cleaner. The valve can be mounted on the charge pipe or, in the case of the first-generation Veloster, the valve is mounted on the intercooler.

Boost control is accomplished both with the wastegate and recirculation valve. More importantly, they work together so the desired boost pressure is achieved, while keeping the turbines spinning so that lag is minimized.

Codes for the valves and actuators are either electrical or they are generated because a command does not provide the desired result. Electrical codes typically indicate a circuit failure, or high or low voltages that point to an open or high resistance for the solenoid’s circuit. Testing the circuit with meters and scopes is part of Hyundai’s diagnostic process.

The engine management system looks at several sensors, including the knock, air/fuel ratio and the boost sensors, to regulate the performance of the engine and turbocharger. Other inputs are used to determine if the boost levels are safe. If there is a malfunctioning sensor, the system will reduce boost pressures and go into a fail-safe mode.

Turbo Damage

One of the more vulnerable areas of any turbocharged engine is the exhaust manifold. Leaks around the gaskets and cracks in the manifold can lead to a loss of power and even oxygen sensor readings.

One item to check if you are dealing with lack-of-power complaint is the turbine’s compressor wheel. If the fins of the compressor are damaged, it can cause poor acceleration, low boost levels and noise. The damage can occur in two ways. First, the turbo can ingest debris. With the wheel spinning in excess of 100,000 rpm, even the smallest rock or piece of metal is like a bullet. Second, the shaft bearings inside the turbo have enough endplay to cause the turbine to make contact with the housing.

You can expect to see a lot more turbos on Hyundai models. The new Stinger and Genesis models are using a twin-turbo V6 that has more than 300 hp.

What Color is the Dipstick?

The Hyundai Theta engine appeared in 2006 Sonata models and is still going strong in naturally aspirated and turbocharged forms in various Hyundai and Kia applications. The one area of the engine that has been the source of more TSBs and tech tips has been the bottom end of the engine and lubrication system.

Part of the problem can be pinned to owners neglecting oil changes; the other part occurred at the factory. Hyundai and Kia have issued multiple recalls for the Theta engine and issues with the oil passages in the crankshaft causing rapid wear to the connecting rod bearings.

According to the recall documents, metallic debris was not removed from the engine crankshaft during the deburring process. The debris restricts oil flow to the connecting rods. The symptom of the damage is a metallic, cyclical knocking noise that is caused by wear of the connecting rod bearings. Some engines have seized due to the damage and even caused fires.

Hyundai’s procedure to determine if there is an issue with the connecting rods involves using its GDS factory scan tool. The procedure tests the engine at specific engine RPM ranges with a special microphone in the dipstick tube. The test will generate a pass or fail result. At the dealer, the tool records a sound file for the warranty department.

In later recall documents, Hyundai and Kia have increased the oil capacity of the vehicle, from 4.6 quarts to 5.0 quarts, noted by a change in the color of the dipstick. On some vehicles, there are three color codes for the dipsticks.

A yellow dipstick is the original dipstick and indicates that the engine has not been inspected. If you see one of these dipsticks, check to see if the recall applies to the vehicle.

An orange dipstick indicates the engine has been tested and passed the test. It can also indicate that the oil capacity could be different than your service information.

The red dipstick means that the engine has been replaced under the recall. If the engine is making a knocking noise, it is now the customer’s fault.


Wear of the connecting rod bearing can occur on any vehicle if the oil change interval is passed, or if the wrong oil is used. If you have a customer who drives a Kia or Hyundai with a Theta engine, the chances are slim that there is an issue with debris in the crankshaft causing wear to the connecting rod bearings. But, neglected maintenance can make the problem occur in Theta engines that don’t have the defect.

Another favor you can do for your customer is to reflash the ECM with the latest calibrations. Hyundai has updated the software to protect the engine and prevent catastrophic engine failure. The knock sensor detection system software continuously monitors engine vibrations for unusual dynamic patterns that develop, as an engine connecting rod bearing wears abnormally in a way that could later cause engine seizure.

If vibrations caused by bearing wear start to occur, the malfunction indicator lamp will blink continuously, an audible chime will sound (in certain models) and the vehicle will be placed in a temporary engine-protection mode with reduced power and acceleration. In this temporary mode, drivers maintain full control of the vehicle as brakes, steering and safety devices, such as airbags, remain operational.

The vehicle can continue to be operated for a limited time in engine-protection mode to enable the customer to safely drive it for inspection and repair. But, acceleration will be slower, with a reduced maximum speed of approximately 60 to 65 mph, and a limited engine speed of around 1,800 to 2,000 rpm.

More details on Hyundai’s engine recalls and the knock sensor product improvement campaign can be found at

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