Your Subaru BRZ’s electrical system provides early warning signs of possible trouble. Each of those warnings has a unique error code to help with the diagnosis.
P0234 is a standard OBD2 trouble code that can occur in the BRZ. In layman’s terms, it indicates a potential problem with an engine’s forced induction system, and you should only see it if your car is turbocharged. Too much boost can trigger the sensor to turn on the check engine light.
This warning code requires immediate attention to prevent costly damage to your BRZ’s engine. You should not drive with P0234. Assuming the engine is getting too much boost, it can blow a head or intake gasket, increasing the repair expense considerably.
It is a generic code. However, the engine type and model year of your Subaru will determine the repair steps needed. This article has been written for a turbocharged vehicle with P0234. It’s rare to find this code on a supercharged vehicle.
P0234: Quick Info
| Definition | Subaru BRZ P0234: Turbocharger or Supercharger “A” Overboost Condition |
| Common Causes | Bad/Damaged Wastegate Valve, Wastegate Control Solenoid, Wastegate Control Hose Blockage, Bad Turbo Charger |
| Symptoms | Check Engine Light, Limp Mode |
| Repair Difficulty? | Difficult, Best Left to a Professional |
| Breakdown Risk? | Yes. Too Much Boost Can Blow the Engine |
Subaru BRZ P0234 Definition: Turbocharger or Supercharger “A” Overboost Condition
Here’s the definition of the P0234 fault code for the BRZ:
Turbocharger or Supercharger
This OBD II trouble code only applies to vehicles that are equipped with a supercharger or turbocharger(s).
Turbochargers and superchargers both provide extra air pressure to the intake manifold. The difference between them is how they accomplish this.
A turbocharger uses exhaust, while a supercharger uses the crankshaft to provide boost.
Overboost Condition
When your BRZ’s Powertrain Control Module (PCM) detects that the pressure buildup has exceeded the vehicle manufacturer’s recommendations, error code P0234 will be logged in its memory.
P0234 Symptoms
Here are the most common symptoms of a P0234 code in the BRZ:
- The check engine light on the dashboard turns on
- There may be a noticeable drop in engine power (limp mode)
- Strange sound coming from the turbocharger/supercharger
- Erratic Idle
- Overheating transmission or engine
- Knocking
P0234 Causes + Diagnosis
It is dangerous to drive a car that has P0234. Overboosting can damage the engine.
When you attempt to fix p0234, start by checking the boost sensor before assuming your BRZ is overboosted.
Repairing P0234 can be challenging, and best left to the professionals, but there are a few things you can do before going that route.
Here’s an excellent order to diagnose possible issues with the P0234 code in the Subaru BRZ:
Are There Other Codes?
The first thing you should do is check for other codes. If there aren’t any codes related to the MAP/MAF or boost sensors, it’s likely a mechanical issue causing P0234.
Examine the Boost Pressure Sensor’s Electrical Connection
If the electrical connection that runs between the your BRZ’s boost pressure sensor circuit has become compromised, the code can illuminate.
Check the wiring harness going to the boost pressure sensor for any damage. Its proximity to the hot exhaust system can cause these wires to become warn and brittle.
Check the Boost Pressure Sensor
Depending on how your BRZ’s turbo is set up, the boost pressure sensor can bolt directly into the turbo system, or it can have a vacuum line that runs to it. The vacuum line type is susceptible to damage.
The boost pressure sensor could also be clogged. If connected via a hose, examine that hose to see if it is cracked or clogged. If it is, clean it out or replace it.
You can test your BRZ’s boost pressure sensor. Here’s an article that details how to test a boost pressure sensor. Keep in mind that P0234 is more often than not caused by a mechanical issue.
Take a Look at the Wastegate Controller
There might be an issue with the wastegate connecting rod. Your BRZ’s owner’s manual should have the recommended PSI for the wastegate controller. If it doesn’t, call the dealer and ask. The rod might need an adjustment.
Is the Wastegate Jammed?
If your car’s wastegate becomes jammed, that will force the turbine to spin faster. That can create an over-boosted engine situation. Typically, this will happen when the connecting rod has become bent.
Faulty turbocharger or supercharger
Sometimes, the most straightforward explanations are the simplest ones. For example, the P0234 code could result from a defective turbocharger or supercharger. Replacing them would clear the code and get your Subaru BRZ back on the road.
We recommend taking your vehicle in to a shop to have it tested before attempting to service the turbo or supercharger yourself.
Conclusion
A P0234 code in the Subaru BRZ is a severe problem. Don’t drive if your vehicle has it. If you do, you risk blowing the engine.
Unfortunately, it is also the type of repair best handled by professional mechanics.