OBD-II Diagnostic Trouble Code
P0108 — Manifold Absolute Pressure/Barometric Pressure Circuit High Input
P0108 means the MAP or barometric pressure signal is above the maximum valid voltage. The ECM reads an impossibly high pressure, usually from an open sensor ground, a signal wire shorted to voltage, or a failed sensor.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Manifold Absolute Pressure/Barometric Pressure Circuit High Input
Code
P0108
Category
Powertrain
Subsystem
Air Flow
Truck-relevant
Yes
What this means for truckers
P0108 (MAP Sensor High Input) — MAP sensor open circuit or shorted to power.
Before you replace parts — try this first
P0108 on the Air Flow system is most often open sensor ground or bad ground connection — 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
Check engine light, possible over-fueling, black smoke, or a derate on diesels, and rich running or rough idle on gas engines. Some trucks run near normal on default values.
Common causes
- CommonOpen sensor ground or bad ground connection ($50–$300)
- OccasionalSignal wire shorted to 5V reference or battery voltage ($100–$450)
- CommonFailed MAP/boost sensor ($120–$400)
- OccasionalWater in the sensor connector ($30–$200)
How to fix
Check the sensor ground for continuity and voltage drop
When to use: First step on P0108
Unplug the sensor and watch whether the signal drops to zero; if not, look for a wiring short
When to use: To decide whether the wiring or the sensor is the problem
Dry and seal the connector and repair corroded pins
When to use: When there is water or corrosion in the connector
Replace the MAP/boost sensor
When to use: When wiring is good and the sensor still reads high
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
- → P0100 — Mass or Volume Air Flow Circuit
- → P0101 — Mass or Volume Air Flow Circuit Range/Performance
- → P0102 — Mass or Volume Air Flow Circuit Low Input
- → P0103 — Mass or Volume Air Flow Circuit High Input
- → P0104 — Mass or Volume Air Flow Circuit Intermittent
Frequently Asked Questions
Can I drive with code P0108?
P0108 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 P0108 on a commercial truck?
Total repair cost ranges $30–$450 depending on the root cause. The cheapest fix is usually the first one listed below — Open sensor ground or bad ground connection — 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 P0108 fail a DOT inspection?
P0108 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 P0108 and related codes?
P0108 is closely related to: P0100 (Mass or Volume Air Flow Circuit), P0101 (Mass or Volume Air Flow Circuit Range/Performance), P0102 (Mass or Volume Air Flow Circuit Low Input), P0103 (Mass or Volume Air Flow Circuit High Input). 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 P0108 is set without the companions, the issue is more isolated.
How do I prevent P0108 from coming back after a repair?
For P0108 (Manifold Absolute Pressure/Barometric Pressure Circuit High Input), 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.