OBD-II Diagnostic Trouble Code
P0242 — Turbocharger Boost Sensor B Range/Performance
Under SAE J2012, P0242 is turbocharger boost sensor B circuit high, though some code lists label it range or performance. The standard meaning is that sensor B voltage is above the maximum expected, usually from an open ground, short to voltage or failed sensor.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Turbocharger Boost Sensor B Range/Performance
Code
P0242
Category
Powertrain
Subsystem
Turbo
Truck-relevant
Yes
What this means for truckers
P0242 (Turbocharger Boost Sensor B Range/Performance) — secondary boost sensor on twin-stage turbos (Cummins ISX dual-stage). Diagnose by comparing primary and secondary boost readings under load.
Before you replace parts — try this first
P0242 on the Turbo system is most often failed boost sensor b — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Derate, low power and check engine light.
Common causes
- CommonFailed boost sensor B ($150–$400)
- CommonOpen sensor ground ($100–$350)
- OccasionalSignal shorted to voltage ($100–$400)
- RareECM fault ($1200–$3500)
How to fix
Check ground and signal at sensor B
When to use: First step
Check for shorts to voltage
When to use: When signal reads high
Replace the sensor
When to use: When wiring is good
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0200 — Injector Circuit Malfunction
- → P0201 — Injector Circuit Malfunction - Cylinder 1
- → P0202 — Injector Circuit Malfunction - Cylinder 2
- → P0203 — Injector Circuit Malfunction - Cylinder 3
- → P0204 — Injector Circuit Malfunction - Cylinder 4
Frequently Asked Questions
Can I drive with code P0242?
P0242 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0242 on a commercial truck?
Total repair cost ranges $100–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Failed boost sensor B — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0242 fail a DOT inspection?
P0242 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0242 and related codes?
P0242 is closely related to: P0200 (Injector Circuit Malfunction), P0201 (Injector Circuit Malfunction - Cylinder 1), P0202 (Injector Circuit Malfunction - Cylinder 2), P0203 (Injector Circuit Malfunction - Cylinder 3). These codes share the same subsystem (turbo) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0242 is set without the companions, the issue is more isolated.
How do I prevent P0242 from coming back after a repair?
For P0242 (Turbocharger Boost Sensor B Range/Performance), prevention centers on the turbo system. Inspect boost piping at every PM service. Replace silicone boost hoses preventively at 250K miles. Run quality diesel fuel (low ash, high cetane) to keep VGT vanes from carbon-locking. After repair, drive 30 miles of mixed-load conditions to let the ECM relearn boost calibration.