OBD-II Diagnostic Trouble Code
P111A — MAF Sensor B Performance
P111A is a manufacturer-specific code; most commonly it means a MAF sensor B performance fault. The ECM saw sensor B readings that do not match expected airflow. Exact meaning varies by OEM.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
MAF Sensor B Performance
Code
P111A
Category
Powertrain
Subsystem
Air Flow
Truck-relevant
Yes
What this means for truckers
Service within a few days on a Cummins X15, Detroit DD15, PACCAR MX-13. Performance is likely degraded. Continuing to drive without service risks additional component damage.
Before you replace parts — try this first
P111A on the Air Flow system is most often dirty or failed maf 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
Poor power, rough running and check-engine light.
Common causes
- CommonDirty or failed MAF sensor B ($150–$500)
- CommonAir leaks in the intake ($100–$400)
- OccasionalRestricted air filter ($40–$150)
- OccasionalWiring fault ($120–$450)
How to fix
Check OEM definition
When to use: First step
Inspect intake for leaks
When to use: Before replacing parts
Clean or replace MAF sensor B
When to use: If dirty or fails testing
Check wiring
When to use: If the code persists
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
- → P1101 — Mass Airflow Sensor Out of Self Test Range
- → P1102 — Mass Airflow Sensor In Range But Lower Than Expected
- → P1103 — Mass Airflow Sensor In Range But Higher Than Expected
- → P110A — Mass Air Flow Sensor Performance
- → P1162 — Throttle Switch Voltage Low
Frequently Asked Questions
Can I drive with code P111A?
P111A 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 P111A on a commercial truck?
Total repair cost ranges $40–$500 depending on the root cause. The cheapest fix is usually the first one listed below — Dirty or failed MAF 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 P111A fail a DOT inspection?
P111A 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 P111A and related codes?
P111A is closely related to: P1101 (Mass Airflow Sensor Out of Self Test Range), P1102 (Mass Airflow Sensor In Range But Lower Than Expected), P1103 (Mass Airflow Sensor In Range But Higher Than Expected), P110A (Mass Air Flow Sensor Performance). These codes share the same subsystem (air-flow) 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 P111A is set without the companions, the issue is more isolated.
How do I prevent P111A from coming back after a repair?
For P111A (MAF Sensor B Performance), prevention centers on the air flow system. Service air filter on time. Clean MAF sensor at every air filter change. Inspect intake boots/hoses for cracks — vibration kills them eventually.