OBD-II Diagnostic Trouble Code
C0249 — Brake Boost Sensor Out of Range
C0249 indicates the brake booster sensor signal is out of range. This sensor measures vacuum or hydraulic pressure available to the brake booster, and the module saw a voltage outside its normal window. The sensor type depends on whether the truck uses vacuum boost or hydraulic (hydro-boost) assist, and the code meaning varies by OEM.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Brake Boost Sensor Out of Range
Code
C0249
Category
Chassis
Subsystem
Brakes
Truck-relevant
Yes
What this means for truckers
C0249 — see existing entry.
Before you replace parts — try this first
C0249 on the Brakes system is most often failed boost pressure / vacuum sensor — 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
Brake or ABS warning lamp on, and on some trucks stability control or hill assist is disabled. If boost is really low the pedal will be hard. Often the only symptom is the warning light when the sensor itself is at fault.
Common causes
- CommonFailed boost pressure / vacuum sensor ($100–$350)
- OccasionalDamaged sensor wiring or connector ($80–$300)
- OccasionalReal low boost from vacuum leak, vacuum pump or power steering supply problem ($150–$900)
- Rare5 V reference circuit shorted by another sensor ($100–$400)
How to fix
Check sensor reading on a scan tool and compare with a mechanical gauge
When to use: To decide if boost is really low or the sensor is wrong
Check 5 V reference, ground and signal at the sensor connector
When to use: Sensor reading is fixed high or low
Inspect vacuum lines, vacuum pump or hydro-boost supply
When to use: Gauge confirms low boost
Replace the sensor
When to use: Wiring and actual boost are 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
- → C0235 — Vehicle Speed Sensor Circuit
- → C0237 — Vehicle Speed Sensor (drive train)
- → C0265 — EBCM Relay Circuit
- → C0277 — Brake Pedal Position Switch Circuit
- → C0282 — Brake Pedal Travel Sensor Circuit
Frequently Asked Questions
Can I drive with code C0249?
Drive with caution. C0249 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix C0249 on a commercial truck?
Total repair cost ranges $80–$900 depending on the root cause. The cheapest fix is usually the first one listed below — Failed boost pressure / vacuum sensor — 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 C0249 fail a DOT inspection?
C0249 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between C0249 and related codes?
C0249 is closely related to: C0235 (Vehicle Speed Sensor Circuit), C0237 (Vehicle Speed Sensor (drive train)), C0265 (EBCM Relay Circuit), C0277 (Brake Pedal Position Switch Circuit). These codes share the same subsystem (brakes) 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 C0249 is set without the companions, the issue is more isolated.
How do I prevent C0249 from coming back after a repair?
For C0249 (Brake Boost Sensor Out of Range), prevention centers on the brakes system. Clean wheel speed sensors at every brake service. Inspect tone rings for cracks or rust. Keep ABS sensor harnesses away from chafe points. Don't drive through deep water that can flood the rear wheel-speed sensor connectors.