P0242🔧 Turbo/supercharger boost pressure sensingStop and fix promptly

P0242: Turbocharger/Supercharger Boost Sensor B Circuit High (Meaning, Causes, Fixes)

Reviewed 2026-10-26 · Based on 2 cited source(s)

What P0242 means

On a turbocharged or supercharged engine, the powertrain control module (PCM) controls boost with a boost control solenoid and watches actual boost with a boost pressure sensor. The PCM sends the sensor a 5 volt reference and gets back a voltage that rises with boost; OBD-Codes.com says zero boost reads about 0.5 volts and maximum boost about 4.5 volts. OBD-Codes.com says P0242 sets when the PCM sees a boost sensor "B" voltage greater than 4 volts at a time when no boost is being commanded. RepairPal describes it more generally as the PCM detecting an incorrect signal from the boost pressure sensor. OBD-Codes.com calls it a generic code for all turbocharged vehicles and names VW, Dodge, Mercedes, Isuzu, Chrysler and Jeep as examples. The sources' cause lists differ: OBD-Codes.com names related sensor codes, intermittent wiring, a short to voltage, the sensor and the PCM, while RepairPal lists a brake booster pressure sensor failure, an exhaust leak, the PCM, the turbo or supercharger and wiring. P0242 is the B-sensor counterpart of P0238 (sensor A circuit high). P0239 to P0241 are the other sensor B codes.

Severity: can I keep driving?

Stop and fix promptly

Get it fixed soon and drive gently until then. RepairPal rates P0242 Urgent, meaning immediate action is needed, and says the engine may go into limp home mode. OBD-Codes.com says that because of the increased risk of catalytic converter damage, the problem should be corrected as soon as possible.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Other codes for the intake air temperature (IAT) sensor, engine coolant temperature (ECT) sensor or 5 volt reference (OBD-Codes.com)
  2. Intermittent wiring or connection problems at or near the sensor (OBD-Codes.com, RepairPal)
  3. The sensor circuit shorted to voltage (OBD-Codes.com)
  4. A faulty boost sensor B (OBD-Codes.com)
  5. A faulty turbocharger or supercharger (RepairPal)
  6. An exhaust leak (RepairPal only)
  7. A brake booster pressure sensor failure (RepairPal only)
  8. A faulty PCM (OBD-Codes.com, RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Scan for other codes first. OBD-Codes.com says any IAT, ECT or 5 volt reference codes must be fixed before diagnosing P0242, and that skipping this step causes many misdiagnoses.
  2. Check for technical service bulletins (TSBs) for your vehicle; there may be a known fix.
  3. Do a wiggle test: with the engine running, gently move the wiring harness near the sensor. If the fault comes and goes, look carefully at the connections in that harness.
  4. With the boost sensor B unplugged and the key on, engine off, measure the voltage on the reference wire with a digital multimeter. OBD-Codes.com says it should be 5 volts and to suspect the PCM if it isn't.
  5. If the reference is good, plug the sensor back in and back-probe the signal wire with the key on, engine off. OBD-Codes.com says it should read about 0.5 volts, and to suspect the sensor if it doesn't.
  6. Don't use an incandescent test light anywhere in the boost sensor circuit; OBD-Codes.com warns against it.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The engine is stuck in limp mode with very poor acceleration
  • You hear new turbo whine or grinding, or see blue smoke
  • The fault is intermittent and the wiggle test doesn't find it
  • You don't have a wiring diagram or a multimeter
  • The code comes back after the wiring and sensor check out

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with a P0242 code?

Only gently and not for long. RepairPal rates it Urgent and says the engine may go into limp mode, and OBD-Codes.com says it should be corrected as soon as possible because of the risk of catalytic converter damage.

What does circuit high mean for P0242?

OBD-Codes.com says the PCM sees boost sensor B reading above 4 volts when no boost is being commanded, so the signal is higher than it can really be. That usually points to the circuit or the sensor rather than real overboost.

What is the difference between P0238 and P0242?

Both mean the boost sensor signal is reading too high. P0238 covers boost sensor A and P0242 covers boost sensor B, which engines with a second turbo or second boost sensor use.

Is P0242 a bad boost sensor?

It can be, but check for other sensor codes and wiring problems first. OBD-Codes.com says other IAT, ECT or 5 volt reference codes must be fixed first, and the voltage checks above tell you whether the sensor is the problem.

How much does it cost to fix P0242?

Neither source gives a repair cost. A wiring or connector repair is usually much cheaper than a sensor or turbo, so get a diagnosis or written estimate before buying parts.

Sources

  1. OBD-Codes.com: P0242 Turbocharger/Supercharger Boost Sensor B Circuit High Input (Daniel Young, ASE Certified Master Technician)
  2. RepairPal: P0242 Turbocharger/Supercharger Boost Sensor "B" Circuit High (rated Urgent)

Last reviewed 2026-10-26. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.