P0242 – Turbo/Super Charger Boost Sensor “B” Circuit High

P0242 is an OBD-II trouble code that points to a problem in your turbocharger or supercharger boost control system, specifically with the “B” boost pressure sensor circuit reading too high. When this code sets, your engine computer (ECU) sees a voltage signal that doesn’t make sense compared to expected boost levels. That can lead to reduced power, limp mode, or even engine protection strategies. Understanding what P0242 means, how it behaves, and how to diagnose it will help you decide whether you can handle it yourself or need a professional.

What Does P0242 Mean?

P0242 stands for “Turbocharger/Supercharger Boost Sensor B Circuit High.” In plain language, the ECU is seeing an abnormally high voltage signal from the “B” boost pressure sensor or its wiring. This usually means the sensor is faulty, the wiring is damaged, or the reference/ground circuit is compromised.

This code appears only on turbocharged or supercharged engines that use multiple boost or pressure sensors. The “B” sensor is typically a secondary boost or manifold pressure sensor used for comparison and redundancy. When its signal is out of range, the ECU sets P0242 and may limit boost to protect the engine.

Quick Reference

• Code: P0242
• Definition: Turbocharger/Supercharger Boost Sensor B Circuit High
• Severity: Moderate to high (can limit power, risk of engine damage if ignored)
• Common Causes: Faulty boost sensor, wiring issues, connector corrosion, ECU reference problems
• Typical Symptoms: Low power, limp mode, check engine light, poor acceleration

Real-World Example / Field Notes

In the shop, I see P0242 most often on turbocharged SUVs and diesel pickups that tow or see a lot of highway miles. One common case: a customer complains the truck “has no power” and won’t climb hills like it used to. Scan shows P0242 stored along with reduced boost on live data. A quick inspection reveals a chafed harness near the turbo, where heat and vibration rubbed through the insulation. Repairing the wiring and securing it away from the hot housing restored normal boost and cleared the code.

Symptoms of P0242

• Check engine light: The MIL will usually illuminate and P0242 will store as an active or pending code.
• Low power / limp mode: The ECU may limit boost, causing sluggish acceleration and poor passing power.
• Poor acceleration: Turbo lag feels worse, and the vehicle may struggle on hills or when towing.
• Reduced fuel economy: Incorrect boost control can cause the engine to run less efficiently.
• Surging or hesitation: Inconsistent boost control can create jerky throttle response under load.
• Unusual turbo noise: You might notice changes in whistle or whoosh sounds if boost is not controlled properly.
• Other boost-related codes: You may see P0240–P0244 or underboost/overboost codes stored alongside P0242.

Common Causes of P0242

Most Common Causes

• Faulty boost pressure sensor B: Internal failure causes the sensor to output a stuck-high or out-of-range voltage.
• Damaged wiring to sensor B: Melted, chafed, or broken wires near the turbo or exhaust cause high signal readings or shorts.
• Corroded or loose connector: Moisture, oil, or road salt in the connector can skew the signal high.
• 5V reference or ground issues: A shared reference circuit problem can raise the sensor signal above normal.
• Improperly installed aftermarket parts: Boost controllers, tunes, or sensors spliced into the harness can distort the signal.

Less Common Causes

• ECU internal fault: Rare, but a failing engine control unit can misread a good sensor as high.
• Boost plumbing issues: Incorrectly routed or pinched vacuum/boost hoses to remote-mounted sensors.
• Previous collision or engine work: Harness pulled tight, pinched, or misrouted during repairs leading to intermittent high signals.
• Water intrusion: Flood damage or deep water crossings causing hidden corrosion in harness splices.
• Incorrect sensor installed: Wrong part number or non-OE sensor with different calibration causing out-of-range voltage.

Diagnosis: Step-by-Step Guide

For diagnosing P0242, you’ll want a basic scan tool (preferably with live data and Mode $06), a quality digital multimeter, and access to wiring diagrams or service information. A smoke machine and lab scope help in tough cases but aren’t mandatory for most DIYers.

1. Confirm the code and check for companions: Scan the vehicle for P0242 and any related boost, MAP, or MAF codes. Note freeze-frame data (RPM, load, boost) when the code set.
2. Visual inspection: Locate Boost Sensor B (often on the intake manifold, charge pipe, or firewall). Inspect the sensor, connector, and nearby harness for heat damage, oil saturation, or rubbing.
3. Check connector condition: Unplug the sensor and look for bent pins, green corrosion, or moisture. Clean with electrical contact cleaner and ensure the connector locks firmly.
4. Verify 5V reference and ground: With key on, back-probe the connector using a multimeter. Confirm you have a stable 5V reference and a solid ground according to the wiring diagram.
5. Measure signal voltage: With the sensor plugged in and engine idling, monitor the signal wire. Typical boost/MAP sensors read around 0.5–1.5V at idle. A stuck-high reading (near 4.5–5V) points to a sensor or wiring fault.
6. Wiggle test the harness: While watching live data or your meter, gently move the harness and connector. If the signal spikes high when you move it, you likely have an internal wire break or short.
7. Compare with other sensors: If your scan tool shows both “Boost Sensor A” and “Boost Sensor B,” compare their readings at idle and under light throttle. B reading drastically higher than A indicates a problem on the B circuit.
8. Check for shared circuit issues: If other sensors on the same 5V reference are also reading high or setting codes, focus on the reference circuit instead of the sensor alone.
9. Substitute a known-good sensor: If wiring checks out and reference/ground are correct, replacing Boost Sensor B with a known-good or new OE-quality sensor is the next step.
10. Clear codes and road test: After repairs, clear codes and perform a controlled road test, watching boost and sensor B data under load to confirm the fix.

Pro tip: Use Mode $06 data (if your scan tool supports it) to see if boost sensor rationality tests are close to failing before the code resets. This can catch intermittent wiring issues that don’t show up immediately.

Possible Fixes & Repair Costs

Most P0242 repairs involve the boost pressure sensor B or its wiring. Common fixes include replacing the boost sensor, repairing or re-routing the harness near the turbo, cleaning or replacing the connector, or in rare cases addressing a 5V reference issue or ECU fault. Depending on your vehicle, a sensor replacement typically runs $75–$250 parts and labor, wiring repairs range from $100–$350, and ECU-related work can exceed $600. Costs vary by vehicle make, shop labor rate, sensor accessibility, and whether additional boost-related problems are found.

• Replace boost pressure sensor B: Install an OE or high-quality aftermarket sensor and clear codes.
• Repair damaged wiring: Splice and solder chafed or melted wires, then protect with heat-resistant loom.
• Clean or replace connector: Address corrosion, broken locks, or burnt terminals with a connector repair kit.
• Correct routing issues: Re-route harness away from hot turbo housings, sharp edges, or moving components.
• Address ECU or reference circuit problems: Diagnose and repair shared 5V reference issues or replace ECU if confirmed faulty.

Can I Still Drive With P0242?

You can usually drive short distances with P0242, but it’s not something you want to ignore for long. Many vehicles will go into a reduced-power or limp mode to protect the engine from potential overboost or incorrect fueling. That means poor acceleration, difficulty merging or towing, and possible safety concerns in traffic. If you notice severe power loss, heavy smoke, or additional warning lights, you should avoid highway driving and get the vehicle inspected as soon as possible.

What Happens If You Ignore P0242?

If you ignore P0242, you risk long-term engine and turbocharger damage. Incorrect boost readings can lead to improper air-fuel ratios, excessive exhaust temperatures, and stress on pistons, valves, and the turbo. At minimum, you’ll live with poor performance and fuel economy. Over time, what started as a simple sensor or wiring issue can snowball into costly mechanical failures.

Last updated: February 13, 2026

Vehicles Commonly Affected by P0242

P0242 shows up most often on turbocharged and supercharged vehicles, including many European and domestic models. You’ll commonly see it on Audi and Volkswagen 1.8T and 2.0T engines, BMW turbocharged inline-4 and inline-6 engines, Ford EcoBoost cars and trucks, GM turbocharged gasoline and Duramax diesel pickups, and various turbocharged Subaru and Mitsubishi performance models. Modern diesel SUVs and pickups that tow frequently are especially prone, due to heat and vibration affecting boost sensors and wiring near the turbo.