P0239 – Turbo/Super Charger Boost Sensor “B” Circuit

P0239 is a turbocharger-related trouble code that can leave you wondering if your engine is about to fail or if it’s just a small sensor issue. This code means your engine computer has detected a problem with the boost pressure signal from the secondary turbo or the “B” side of a twin-turbo system. In many cases, you’ll notice low power, a check engine light, and sometimes strange turbo noises. The good news: with a logical diagnosis and a few basic tools, you can often pinpoint the cause without guessing.

What Does P0239 Mean?

P0239 stands for “Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance.” In plain terms, the ECU sees a mismatch between the boost pressure it expects and the signal it actually gets from the boost pressure sensor on the “B” side (often the secondary turbo or a second sensor).

This can be caused by a faulty sensor, wiring issues, or an actual boost problem such as leaks or sticking turbo vanes. The ECU compares boost pressure to engine load, RPM, and sometimes the MAP sensor or MAF sensor. When the readings don’t line up for a certain time, it stores P0239 and usually turns on the check engine light.

Quick Reference

• Code: P0239
• Meaning: Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance
• Typical Symptoms: Low power, limp mode, check engine light, possible whistling or whooshing
• Common Causes: Boost sensor fault, wiring issues, boost leaks, turbo problems
• Severity: Moderate to high – can damage engine or turbo if ignored

Real-World Example / Field Notes

In the shop, I see P0239 most often on turbocharged diesels and smaller turbo gas engines. One example: a customer with a 2.0L turbo SUV complained of “no power” and heavy fuel use. Scan showed P0239 and low boost. Visual inspection found a charge pipe clamp loose after a DIY air filter install. Tightened the clamp, cleared the code, and boost came back to normal. On another case, a diesel pickup had the same code, but this time it was a chafed wire to the boost sensor rubbing on a bracket. A simple harness repair fixed a problem that looked like a bad turbo at first glance.

Symptoms of P0239

• Check engine light on: The MIL will almost always illuminate when P0239 is stored.
• Low power or sluggish acceleration: The ECU may limit boost to protect the engine, making the vehicle feel “flat.”
• Limp mode: Some vehicles go into a reduced-power strategy, especially under heavy load or towing.
• Poor fuel economy: Incorrect boost often leads to inefficient combustion and higher fuel use.
• Unusual turbo noises: Whistling, whooshing, or hissing can point to boost leaks or turbo issues.
• Black smoke (mostly diesels): Excess fuel with low boost can cause soot and visible exhaust smoke.
• Surging or uneven power: Intermittent sensor or wiring problems can cause fluctuating boost levels.

Common Causes of P0239

Most Common Causes

• Faulty boost pressure sensor “B”: Internal sensor failure, contamination from oil mist, or water intrusion can skew the voltage signal.
• Wiring or connector issues: Corroded pins, loose connectors, broken wires, or shorts between the sensor and ECU are very common.
• Boost leaks: Cracked intercooler, split hoses, loose clamps, or damaged charge pipes cause actual boost to differ from expected values.
• Sticking wastegate or boost control valve: If the wastegate is stuck open or the control solenoid is malfunctioning, the turbo can’t build proper boost.
• Vacuum or pressure line problems: On systems that use vacuum lines to control the turbo, leaks or broken lines will cause incorrect boost control.

Less Common Causes

• Turbocharger mechanical failure: Worn bearings, damaged compressor wheel, or stuck variable-geometry vanes can trigger P0239.
• ECU software or internal fault: Rare, but possible after tuning, reflashing, or water damage to the ECU.
• Aftermarket modifications: Poorly calibrated tunes, larger turbos, or non-stock boost controllers can confuse the ECU’s expected boost map.
• Restricted intake or exhaust: Severely clogged air filter, collapsed intake hose, or blocked exhaust can affect boost behavior.
• Shared sensor reference issues: A shorted 5V reference line shared with other sensors can pull the boost sensor signal out of range.

Diagnosis: Step-by-Step Guide

You’ll want a basic OBD-II scan tool (preferably with live data), a digital multimeter, and simple hand tools. A smoke machine or boost leak tester is very helpful but not mandatory. Access to a wiring diagram and service information for your specific vehicle is a big plus.

1. Confirm the code and check for companions: Scan for DTCs. Note any related boost, MAP, MAF, or sensor reference codes (like P0235, P0101). Multiple codes can point you toward wiring or power supply issues.
2. Inspect the intake and charge pipes: With the engine off, inspect turbo hoses, intercooler, and clamps. Look for oil residue trails, splits, or loose connections. Wiggle the pipes and check for cracks or soft spots.
3. Check the boost sensor “B” and connector: Locate the sensor (usually on or near the intercooler pipe or intake manifold). Inspect for broken tabs, corrosion, oil contamination, or bent pins. Clean the connector and reseat it firmly.
4. Verify sensor wiring: Using a wiring diagram, check for 5V reference, ground, and signal at the sensor with a multimeter. A missing 5V or bad ground points to wiring or ECU issues, not the sensor itself.
5. Monitor live data: With the scan tool, watch boost or MAP readings at idle and under light throttle. Compare sensor B to sensor A (if equipped). Readings that are stuck, jumpy, or way off from expected values suggest a sensor or wiring problem.
6. Check boost control components: Inspect the wastegate actuator, vacuum lines, and boost control solenoid. Make sure the actuator rod moves freely and vacuum lines are not cracked or disconnected.
7. Test for boost leaks: If available, use a smoke machine or boost leak tester on the intake system. Listen for hissing and watch for smoke escaping around clamps, intercooler, or plastic pipes.
8. Evaluate turbo condition: With the intake tube removed, gently check turbo shaft play (engine off, cool). Excessive movement, damaged blades, or scraping sounds indicate a failing turbo.
9. Check Mode $06 (if supported): Some scan tools can access Mode $06 data to see if boost or MAP tests are marginal before they set a hard code. This can help catch intermittent issues.
10. Clear codes and road test: After repairs or inspections, clear P0239 and perform a controlled test drive. Monitor boost, fuel trims, and related PIDs to confirm the fix.

Pro tip: Don’t replace the turbo just because you see P0239. In practice, sensors, wiring, and leaks are far more common. Always verify actual boost with live data and a thorough visual inspection first.

Possible Fixes & Repair Costs

Repairs for P0239 range from simple hose fixes to full turbo replacement. A loose clamp or small boost leak may cost $0–$150 to diagnose and repair. Replacing a boost pressure sensor typically runs $100–$300 parts and labor. Wiring repairs, depending on access, can be $150–$400. If the turbocharger itself is damaged, expect $900–$2,500 or more, especially on diesel trucks or vehicles with twin turbos. Costs vary based on vehicle make, labor rates in your area, and whether you use OEM or aftermarket parts.

Can I Still Drive With P0239?

You can usually drive short distances with P0239, but it’s not ideal. Many vehicles will limit boost, so you’ll notice reduced power, especially on hills or while towing. If you hear loud turbo noises, see heavy smoke, or feel severe loss of power, avoid driving and have it inspected immediately. Continuing to drive hard with incorrect boost can overheat the turbo, stress pistons and head gaskets, and lead to more expensive repairs.

What Happens If You Ignore P0239?

Ignoring P0239 can turn a minor issue into a major failure. A small boost leak or sensor problem can eventually cause turbo overspeed, excessive exhaust temperatures, and carbon buildup. On diesels, prolonged low boost can lead to clogged DPFs and EGR issues. Over time, you risk turbocharger failure, engine damage, and significantly higher repair bills.

Last updated: February 13, 2026

Vehicles Commonly Affected by P0239

P0239 is common on many turbocharged vehicles, especially modern diesels and small-displacement gas engines. You’ll often see it on Ford Power Stroke, GM Duramax, and Ram Cummins diesel trucks, as well as VW and Audi TDI models. It also appears on turbocharged Subaru, Hyundai, Kia, Ford EcoBoost, and various European makes like BMW and Mercedes-Benz. Any vehicle with a twin-turbo setup or multiple boost sensors is more likely to set a “B” circuit code like P0239 when something in the boost path isn’t right.