OBD-II trouble code
P0235: Turbocharger/Supercharger Boost Sensor "A" Circuit Malfunction
The boost pressure sensor circuit has an electrical fault — the engine computer can't trust its boost reading, so it typically limits boost to protect the engine.
Quick facts
- System
- Powertrain
- Category
- Fuel & Air
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $400
- DIY difficulty
- Intermediate DIY
What does P0235 mean?
Turbocharged and supercharged engines use a boost pressure sensor so the computer can measure how much pressure the charger is actually making and control it precisely. P0235 is the general circuit-malfunction code for boost sensor "A": the signal is missing, stuck, or electrically implausible — the parent code to P0237 (signal low) and P0238 (signal high).
Because overboost can destroy an engine quickly, the computer responds conservatively when it loses this signal: it usually caps boost or enters reduced-power mode. That's why the dominant symptom is a noticeable lack of power rather than anything dramatic.
Most cases trace to wiring — the sensor lives in a hot, vibrating environment on or near the intake/charge pipe — or to the sensor itself getting contaminated with oil residue from the charge air. Check connector, reference voltage, and ground before condemning the sensor, and make sure the sensor's port or hose isn't blocked or leaking.
Common causes
- Failed boost/charge pressure sensor
- Corroded, loose, or oil-contaminated connector
- Open or shorted wiring in the sensor circuit
- Missing 5-volt reference or poor ground
- Blocked or leaking sensor port/hose
- Oil fouling of the sensor element (common on high-blowby engines)
Symptoms
- Check engine light on
- Noticeable power loss (boost limited/limp mode)
- Hesitation under load
- Implausible or frozen boost reading on live data
- Occasionally rough idle
Diagnostic steps
- 1.Scan for companion codes (P0236-P0238, underboost/overboost codes) and record freeze-frame.
- 2.Key on, engine off: the boost sensor should read close to barometric pressure — a wildly different value points at sensor or circuit.
- 3.Inspect connector and wiring for corrosion, chafing, and oil intrusion.
- 4.Verify 5-volt reference and ground at the connector.
- 5.Check the sensor port/hose for blockage, cracks, or oil pooling; clean carefully if contaminated.
- 6.Replace the sensor if the circuit checks good; clear codes and confirm normal boost on a road test.
Repair cost
$100 – $400
Boost/MAP-style sensors run $40-$150 and are usually accessible, so most repairs land near the low end. Wiring repairs vary. If oil contamination caused it, address excessive blowby or a leaking turbo seal or the new sensor will foul too.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with check engine light diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.