OBD-II trouble code
P0241: Turbocharger/Supercharger Boost Sensor "B" Circuit Low
The signal from the second boost pressure sensor has fallen below its valid range. A short to ground, an open in the signal wire, or a missing 5-volt reference all produce this — and the reference is worth checking first, because losing it takes several sensors down at once.
Quick facts
- System
- Powertrain
- Category
- Fuel & Air
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $950
- DIY difficulty
- Intermediate DIY
What does P0241 mean?
A boost pressure sensor is a three-wire device. It receives a 5-volt reference from the module, it receives a ground, and it returns a signal voltage that rises and falls with pressure. P0241 sets when the signal voltage coming back from sensor "B" drops below the lowest value the module considers physically possible — typically somewhere around a couple of tenths of a volt, though the exact threshold is calibration-specific.
There are three ways a signal gets that low, and they are worth separating because the tests differ. The signal wire can be shorted to ground, which drags it down to essentially zero. The signal wire can be open, in which case the module's internal pull-down leaves the input sitting near ground and reads it as low. Or the 5-volt reference feeding the sensor can be missing, in which case the sensor has nothing to work with and cannot produce any meaningful output no matter how healthy it is.
That third possibility deserves to be checked first, and here is why: the 5-volt reference is almost never dedicated to one sensor. Modules typically supply several sensors from the same reference circuit. So if that reference has been lost or shorted, you will normally see codes from other sensors on the same circuit at the same time — throttle position, MAP, pedal position, fuel rail pressure, and similar. If P0241 arrived alone, a shared reference fault is unlikely and you can move on quickly. If P0241 arrived with a cluster of unrelated sensor codes, checking the reference at a couple of those sensors takes five minutes and can replace the entire rest of the diagnosis.
Because this is sensor "B", the second sensor gives you something most single-sensor diagnoses lack: a known-good reference. Sensor "A" and sensor "B" should both report roughly barometric pressure with the key on and the engine off. If "A" reads plausibly and "B" reads at or near zero in that state, you have confirmed the fault is real and localized to "B" without leaving the driveway. You can also use the healthy sensor as a comparison for connector condition, pin fit, and expected voltage values.
What the module does about it is fairly consistent. A boost signal it cannot trust is not something it will build a boost strategy on, so it substitutes a default value and typically caps boost or enters a reduced-power mode. On twin-turbo and sequential systems the effect is more pronounced, because coordinating two turbochargers on one trustworthy signal is not something the calibration will attempt. On engines where the "B" sensor exists only to monitor charge air cooler efficiency, the practical effect may be no more than the warning light and slightly conservative fueling.
The physical causes cluster around the harness rather than the sensor. Boost sensors live in the charge air path, which on most engines means heat, vibration, and — on the post-intercooler position common to diesels — a location near the front of the vehicle where road spray, salt, and stone impact all reach. Water-intruded connectors and chafed harness sections are more likely here than a sensor that has simply died.
Common causes
- Signal wire shorted to ground
- Open or broken signal wire between sensor "B" and the module
- Missing or shorted 5-volt reference at the sensor — check first if other sensor codes are present
- Corroded, water-intruded, or loose connector at the second boost sensor
- Chafed or heat-damaged harness where it passes the turbo, exhaust, or charge piping
- Spread, backed-out, or pushed-in terminals in the sensor connector
- Failed boost pressure sensor "B" reading low internally
- Wrong-range or incorrect replacement sensor fitted to the "B" position
- Damaged harness at the front of the vehicle on post-intercooler sensor locations, from road spray, salt, or stone impact
- PCM internal fault on that sensor input, rare and only diagnosed after everything else checks out
Symptoms
- Check engine light with P0241 stored
- Reduced power or a boost cap, most noticeable on twin-turbo and sequential systems
- Reduced-power or limp mode
- Boost pressure reading at or near zero in live data regardless of engine load
- Sluggish throttle response and poor acceleration
- Poor fuel economy
- Black smoke on diesel applications where fueling compensation is affected
- Additional sensor codes at the same time if a shared 5-volt reference has been lost
Diagnostic steps
- 1.Record every stored code before touching anything. A cluster of unrelated sensor codes alongside P0241 strongly suggests a shared 5-volt reference fault rather than a sensor fault.
- 2.Identify which physical sensor your engine calls boost sensor "B" from service data, since it may be a second-turbo sensor, a sequential-handover sensor, or a post-intercooler sensor.
- 3.With the key on and the engine off, compare sensor "A" and sensor "B" in live data. Both should read roughly barometric. "B" at or near zero while "A" reads plausibly confirms the fault is local to "B".
- 4.Measure the 5-volt reference at the sensor "B" connector with the key on. No reference means the fault is upstream in the reference circuit, not in the sensor.
- 5.Check the sensor ground for low resistance to a known-good ground point, not just continuity.
- 6.Inspect the connector closely for corrosion, water intrusion, green deposits on the pins, and spread or backed-out terminals.
- 7.With the sensor unplugged and the key on, measure the signal wire at the module side. A signal wire shorted to ground will show near zero volts with the sensor disconnected.
- 8.Check continuity end to end on the signal wire to rule out an open, and check it for a short to ground with the connector disconnected at both ends.
- 9.Follow the harness run visually, paying attention to anywhere it passes the turbocharger, exhaust manifold, or charge piping, and to the front-of-vehicle section on post-intercooler installations.
- 10.Back-probe the signal wire and wiggle-test the harness while watching live data for dropouts, since intermittent low readings are common.
- 11.Replace the sensor only after the reference voltage, ground, signal wire, and connector have all tested good.
Repair cost
$100 – $950
The sensor is typically $60-$250 in parts. Labor depends heavily on the "B" location — a sensor in accessible charge piping is a 20-minute job, while a post-intercooler sensor behind bumper structure can take two hours, so the common repair falls between $100 and $450. Connector and terminal repairs are often $100-$250. Repairing a chafed or heat-damaged harness section generally runs $150-$450 because the labor is in tracing it, not in the parts. Diagnosis commonly runs $100-$180. The upper end covers cases where a shared reference circuit fault has to be traced back through the harness, or where a damaged section must be replaced rather than spliced.
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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.