OBD-II Diagnostic Trouble Code
C1418 — Brake Boost Vacuum Low
C1418 indicates brake booster vacuum is low. The module saw vacuum below the threshold needed for proper brake assist. Definitions vary by OEM; it applies to vacuum-boosted brakes.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Brake Boost Vacuum Low
Code
C1418
Category
Chassis
Subsystem
Brakes
Truck-relevant
Yes
What this means for truckers
C1418 (Brake Boost Vacuum Low) — insufficient vacuum for power brake assist. Pedal will feel hard. Check vacuum source.
Before you replace parts — try this first
C1418 on the Brakes system is most often vacuum leak in hoses or booster — 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
Hard brake pedal, longer stopping distance and brake warning lamp on. Symptoms may be worse after several brake applications at idle.
Common causes
- CommonVacuum leak in hoses or booster ($50–$600)
- CommonWeak or failed vacuum pump ($400–$1200)
- OccasionalStuck check valve ($30–$150)
- OccasionalFailed vacuum sensor reading falsely low ($100–$350)
How to fix
Check vacuum with a gauge at the booster
When to use: First step
Inspect hoses and the check valve
When to use: Low vacuum
Test vacuum pump output
When to use: Hoses and check valve good
Replace the booster
When to use: Booster will not hold vacuum
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
Frequently Asked Questions
Can I drive with code C1418?
Drive with caution. C1418 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 C1418 on a commercial truck?
Total repair cost ranges $30–$1200 depending on the root cause. The cheapest fix is usually the first one listed below — Vacuum leak in hoses or booster — 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 C1418 fail a DOT inspection?
C1418 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 C1418 and related codes?
C1418 is closely related to: C1417 (Brake Boost Vacuum Sensor Performance), C1429 (Stability Control Sensor Power 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 C1418 is set without the companions, the issue is more isolated.
How do I prevent C1418 from coming back after a repair?
For C1418 (Brake Boost Vacuum Low), 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.