What P0242 means
Boost sensor B is a second boost pressure sensor, for a second turbo or bank on parallel twin-turbo engines or a second stage on two-stage systems.
How the engine computer detects it
No manufacturer using sensor B codes was found – GM, Ford and Saab, even on two-stage and twin-turbo engines, use a single boost sensor; the description follows CARB and the documented sensor A codes. P0242 means the signal of sensor B is above its upper limit – for sensor A, GM uses 86 % of 5 V and Ford 4.88 V for 5 s. Causes are a short to voltage, an open ground or, on a pulled-up input, an open signal wire.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Loss of power, limp mode
- Boost B shows its maximum value
Common causes
- Sensor ground open, or signal wire open on a pulled-up input Most likely
- Signal shorted to 5 V or 12 V Possible
- Sensor faulty internally Possible
- Engine module Less likely
How to diagnose P0242
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: boost pressure sensor b, sensor wiring, charge air hoses.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 2
- Fuel and air metering (injector circuit)
- 42
- Specific fault
Questions drivers ask
Can I drive with code P0242?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P0242?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Can I fix P0242 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.