Home OBDII DTC Doctor P0108 Code Explained: Manifold Absolute Pressure (MAP) / Barometric Pressure Circuit High Input Causes, Symptoms & Fixes

P0108 Code Explained: Manifold Absolute Pressure (MAP) / Barometric Pressure Circuit High Input Causes, Symptoms & Fixes

If your OBD-II scanner displays P0108, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the Manifold Absolute Pressure (MAP) or Barometric Pressure (BARO) sensor signal voltage is higher than the calibrated maximum.

The generic OBD-II definition for P0108 is:

Manifold Absolute Pressure/Barometric Pressure Circuit High Input

Unlike P0106, which indicates that the pressure signal is implausible or outside its expected performance range, P0108 specifically means the electrical signal voltage is too high.

Most analog MAP sensors operate on a five-volt reference circuit and produce a signal that changes with intake-manifold pressure. When the PCM sees a voltage near the top of the sensor’s range for too long, especially when engine conditions do not justify it, P0108 is stored.

A high signal may be caused by a failed MAP sensor, an open ground circuit, a signal wire shorted to voltage, damaged wiring, connector corrosion, a restricted vacuum hose, excessive manifold pressure, or a shared five-volt reference problem.

In plain English, the PCM believes the intake manifold is constantly under extremely heavy load, near atmospheric pressure, or under boost—even when the engine is idling and clearly has other plans.

Alternate Manufacturer Definitions

Depending on the manufacturer, service manual, or scan tool, P0108 may also appear as:

MAP Sensor Circuit High Input
Manifold Absolute Pressure Circuit High
MAP/BARO Sensor High Voltage
Intake Manifold Pressure Sensor High Input
MAP Sensor Signal Too High
Barometric Pressure Sensor Circuit High
Absolute Pressure Sensor High Voltage
MAP Sensor Electrical High
Intake Pressure Sensor High Signal
MAP Sensor Voltage Above Threshold
Boost Pressure Sensor High Input
Manifold Pressure Sensor Signal High

Although the terminology varies, each definition indicates that the PCM is receiving an abnormally high electrical signal from the MAP or BARO sensor circuit.

P0108 Quick Facts

Item	Information
Diagnostic Code	P0108
Generic Definition	MAP/BARO Circuit High Input
Category	Powertrain
System	Air Intake / Engine Management
Fault Type	High Signal Voltage
Severity	Moderate to High
Safe to Drive?	Sometimes, depending on symptoms
Common Causes	Faulty MAP sensor, open ground, signal shorted to voltage
Common Symptoms	Rough idle, rich running, hesitation, reduced power
Typical Repair Cost	$40–$1,200+

What Does the P0108 Code Mean?

The MAP sensor measures pressure inside the intake manifold and sends a corresponding voltage signal to the PCM.

The PCM uses this information to calculate:

Engine load
Air density
Fuel delivery
Ignition timing
EGR operation
Turbocharger boost
Transmission shift strategy
Emissions-system operation

When MAP signal voltage remains higher than expected, the PCM may interpret the engine as operating under heavy load.

If that reading does not agree with throttle position, engine speed, airflow, or other sensor data, the PCM stores P0108.

What Does “High Input” Mean?

A high-input code means the voltage on the MAP or BARO signal circuit is above the expected limit.

It does not automatically mean actual manifold pressure is too high.

Possible electrical causes include:

Signal wire shorted to the five-volt reference
Signal wire shorted to battery voltage
Open or high-resistance sensor ground
Failed MAP sensor
Connector terminal damage
Internal PCM input fault

The PCM may receive a value close to five volts even when the engine is idling under high vacuum.

What Is the MAP Sensor?

The Manifold Absolute Pressure sensor measures absolute pressure inside the intake manifold.

It helps the PCM determine how much air is entering the engine and how heavily the engine is being loaded.

The MAP sensor may be:

Mounted directly on the intake manifold
Connected through a vacuum hose
Integrated with an Intake Air Temperature sensor
Combined with a boost-pressure sensor
Used with or without a Mass Air Flow sensor

On speed-density systems, the MAP sensor is one of the primary inputs used to calculate airflow.

How the MAP Sensor Works

Most MAP sensors contain:

A pressure-sensitive diaphragm
Internal electronic circuitry
A five-volt reference circuit
A sensor ground
A signal wire

As intake-manifold pressure changes:

The diaphragm flexes.
Internal resistance changes.
Signal voltage changes.
The PCM converts voltage into pressure.

A typical analog MAP sensor may produce approximately:

Operating Condition	Typical Voltage
Key On, Engine Off	4.0–4.8 V
Warm Idle	0.9–1.8 V
Light Cruise	1.5–2.8 V
Heavy Acceleration	3.5–4.5 V
Turbocharged Boost	May approach upper sensor range

Exact voltage depends on the sensor design, altitude, and vehicle calibration.

Why MAP Voltage Rises with Engine Load

At idle, the throttle is mostly closed and manifold vacuum is high.

High vacuum means low absolute pressure, so MAP voltage is normally relatively low.

As the throttle opens:

Manifold vacuum decreases
Absolute pressure increases
MAP signal voltage rises
PCM-calculated engine load increases

P0108 may set when voltage remains high even though the throttle is closed and the engine should be producing substantial vacuum.

What Is the BARO Sensor?

The Barometric Pressure sensor measures outside atmospheric pressure.

Depending on the vehicle, the BARO function may be provided by:

A separate BARO sensor
The MAP sensor during key-on
A combined MAP/BARO sensor
A sensor integrated into the MAF assembly
A turbocharger pressure sensor

The PCM uses BARO information to compensate for altitude, weather, air density, and boost-control requirements.

How the PCM Detects P0108

The PCM compares MAP or BARO voltage with several other inputs.

These may include:

Throttle position
Engine RPM
MAF airflow
Accelerator pedal position
Intake Air Temperature
Engine Coolant Temperature
Fuel trims
Oxygen sensor activity
Turbocharger boost command
EGR position

P0108 may set when:

MAP voltage exceeds the maximum threshold
Signal voltage remains near five volts
MAP pressure stays near atmospheric pressure at idle
MAP does not decrease after the engine starts
MAP disagrees with throttle position
MAP and BARO values remain identical while the engine is running
Pressure readings indicate boost when none is commanded

Some vehicles require the high-voltage condition to remain present for several seconds before storing the code.

P0108 vs P0105, P0106, P0107 and P0109

Code	Description	General Fault
P0105	MAP/BARO Circuit Malfunction	General circuit fault
P0106	MAP/BARO Range/Performance	Implausible or inaccurate signal
P0107	MAP/BARO Circuit Low Input	Signal voltage too low
P0108	MAP/BARO Circuit High Input	Signal voltage too high
P0109	MAP/BARO Circuit Intermittent	Signal cuts in and out

An easy way to remember the group:

P0105: The circuit has a general problem.
P0106: The reading makes no sense.
P0107: The voltage is too low.
P0108: The voltage is too high.
P0109: The signal is unstable.

Common Symptoms of P0108

Symptoms depend on whether the PCM substitutes a default value and how inaccurate the sensor signal becomes.

Common symptoms include:

Check Engine Light
Rough idle
High idle
Hard starting
Extended cranking
Engine hesitation
Poor acceleration
Reduced engine power
Limp mode
Engine stalling
Rich fuel mixture
Black exhaust smoke
Fuel odor
Poor fuel economy
Spark plug fouling
Engine misfires
Failed emissions inspection
Turbocharger boost problems
Harsh or unusual transmission shifting

Some vehicles may show only a warning light, especially if the PCM quickly substitutes a calculated MAP value.

Can P0108 Cause a Rich Fuel Mixture?

Yes.

A high MAP signal may tell the PCM that the engine is under heavy load.

The PCM may respond by increasing injector pulse width and enriching the fuel mixture.

Possible symptoms include:

Black exhaust smoke
Fuel odor
Poor fuel economy
Carbon buildup
Spark plug fouling
Rough idle
Catalytic converter damage

Can P0108 Cause Hard Starting?

Yes.

During startup, the PCM uses MAP or BARO data to estimate air density and engine load.

If the sensor reports excessive pressure, the PCM may command too much fuel.

This can cause:

Extended cranking
Flooded-engine symptoms
Rough startup
Immediate stalling
Fuel smell from the exhaust

Can P0108 Cause Engine Stalling?

It can.

An excessively high MAP signal may cause unstable fueling and ignition timing, particularly at idle and during deceleration.

The engine may stall:

Shortly after startup
When coming to a stop
When the throttle closes
When shifting into gear
When electrical loads are added

Can P0108 Cause Misfires?

Yes.

If the PCM adds excessive fuel because it believes the engine is under heavy load, the mixture may become too rich to burn properly.

Related trouble codes may include:

P0300
P0301
P0302
P0303
P0304
P0172
P0175

A flashing Check Engine Light indicates active misfires that may damage the catalytic converter.

Can P0108 Affect Transmission Shifting?

Yes.

Automatic transmissions often use calculated engine load to determine:

Shift timing
Line pressure
Downshift strategy
Torque-converter lockup

A falsely high engine-load signal may result in:

Delayed shifts
Harsh shifts
Higher shift RPM
Unnecessary downshifts
Poor fuel economy

The transmission may be reacting to bad engine data rather than suffering an internal failure.

Can P0108 Affect Turbocharged Engines?

Absolutely.

On turbocharged engines, the MAP or TMAP sensor may monitor both manifold pressure and boost.

A high signal can cause the PCM to:

Disable boost
Open the wastegate
Limit throttle
Enter limp mode
Store overboost-related codes
Substitute a calculated pressure value

Possible causes on turbocharged vehicles include:

Failed pressure sensor
Signal wire shorted to voltage
Open sensor ground
Incorrect sensor scaling
Improper aftermarket tune
Actual overboost condition
Wastegate control fault

Is P0108 Serious?

P0108 should be considered a moderate to serious fault.

The vehicle may remain drivable, but inaccurate load calculations can affect fueling, ignition timing, boost control, and transmission behavior.

Ignoring P0108 may cause:

Poor fuel economy
Increased emissions
Stalling
Reduced power
Rich operation
Spark plug fouling
Catalytic converter damage
Turbocharger control problems

Prompt diagnosis is recommended.

Can You Drive with P0108?

Short-distance driving may be possible if:

The engine runs smoothly
Acceleration remains predictable
The Check Engine Light is steady
No black smoke is present
The vehicle has not entered limp mode

Avoid driving if:

The engine stalls
The Check Engine Light flashes
Heavy misfires occur
Black smoke is visible
Fuel odor is severe
Turbocharger boost becomes unstable
Reduced power makes traffic merging unsafe

Can a Signal Wire Shorted to Voltage Cause P0108?

Yes.

A signal wire contacting the five-volt reference circuit can cause the PCM to see a constantly high MAP value.

Possible locations include:

Chafed harness sections
Pinched wiring
Connector damage
Improper previous repairs
Melted insulation
Aftermarket wiring splices

A short to battery voltage may also occur, although many PCM circuits are not designed to tolerate it.

Can an Open Ground Cause P0108?

Yes.

An open or high-resistance sensor ground can force the signal voltage upward.

Possible causes include:

Broken ground wire
Corroded splice
Loose terminal
Damaged connector
Poor PCM ground
Loose engine ground strap

Ground faults are among the most common non-sensor causes of P0108.

Can a Vacuum Hose Problem Cause P0108?

Yes, particularly on remotely mounted MAP sensors.

A disconnected, cracked, blocked, or incorrectly routed vacuum hose may prevent the sensor from seeing actual manifold vacuum.

If the sensor remains exposed to atmospheric pressure, its voltage may stay high even while the engine idles.

Can Actual Low Engine Vacuum Cause P0108?

In some cases.

The sensor may be accurately reporting unusually high manifold pressure caused by:

Large vacuum leak
Incorrect valve timing
Low compression
Burned valves
Stuck EGR valve
Restricted exhaust
Aggressive aftermarket camshaft

However, purely mechanical problems more commonly trigger P0106 than a dedicated high-input electrical code.

Can a Bad MAP Sensor Cause P0108?

Yes.

Internal sensor failure may cause the signal to remain near the five-volt reference level regardless of actual manifold pressure.

A failed sensor may also exhibit:

Flat signal
Delayed response
Intermittent high voltage
Incorrect pressure readings
Temperature-sensitive failure

Always verify reference voltage, ground, and signal wiring before replacing the sensor.

25 Common Causes of P0108

The most common causes include:

Failed MAP sensor
MAP signal wire shorted to the five-volt reference
MAP signal wire shorted to battery voltage
Open sensor ground circuit
High resistance in the sensor ground
Loose MAP sensor connector
Corroded connector terminals
Bent or spread connector pins
Water intrusion in the connector
Oil contamination in the connector
Damaged wiring harness
Melted wiring near hot engine components
Improper previous wiring repair
Disconnected MAP vacuum hose
Cracked MAP vacuum hose
Blocked or restricted MAP vacuum hose
Restricted MAP sensor port
Faulty BARO sensor
Shared five-volt reference fault
Incorrect aftermarket MAP sensor
Incorrect sensor calibration or tuning
Actual turbocharger overboost condition
Incorrect engine timing
Internal PCM software or calibration fault
Internal PCM failure

The most common causes are a failed sensor, missing ground, shorted signal wiring, connector damage, or a vacuum hose that prevents the sensor from seeing actual manifold pressure.

Failed MAP Sensor

A failed MAP sensor may produce permanently high voltage because of:

Internal electronic damage
Heat exposure
Vibration
Oil contamination
Moisture intrusion
Age
Electrical overload

The sensor may remain stuck near its maximum output even when manifold vacuum changes.

Open or High-Resistance Ground

A poor ground is one of the most important causes of P0108.

When the sensor cannot complete its ground path correctly, signal voltage may rise toward the reference-voltage level.

Inspect:

Sensor ground wire
Ground splices
PCM grounds
Engine ground straps
Connector terminal tension
Corrosion under ground fasteners

A simple continuity test may not reveal resistance under load, so voltage-drop testing is preferred.

Signal Wire Shorted to Voltage

A damaged signal wire may contact:

Five-volt reference wiring
Battery-feed wiring
Injector power circuits
Alternator wiring
Aftermarket accessories

This may produce a constant high signal even with the MAP sensor unplugged.

Harness inspection and circuit-isolation testing are required to locate the short.

Vacuum Hose and Sensor-Port Problems

Some MAP sensors are connected to the intake manifold through a hose.

If that hose becomes disconnected or blocked, the sensor may remain exposed to atmospheric pressure instead of manifold vacuum.

This may cause a high signal at idle.

Inspect for:

Kinks
Carbon blockage
Oil saturation
Cracks
Loose fittings
Incorrect hose routing

Incorrect Aftermarket Sensor or Tune

A sensor may physically fit while using a different pressure range or voltage calibration.

This is common on:

Engine swaps
Turbo conversions
High-boost builds
Standalone engine-management systems
Vehicles using three-bar or four-bar MAP sensors

If the PCM calibration does not match the installed sensor, the voltage may appear excessively high.

Actual Overboost Condition

On turbocharged engines, P0108 may occasionally be caused by real manifold pressure exceeding the expected limit.

Possible causes include:

Stuck wastegate
Damaged wastegate hose
Faulty boost control solenoid
Incorrect boost controller setting
Improper tune
Restricted wastegate flow
Turbocharger modification

Actual boost pressure should be compared with commanded boost before assuming the sensor circuit is defective.

PCM Failure

PCM failure is possible but uncommon.

Before replacing or programming the module, verify:

Sensor reference voltage
Sensor ground
Signal-wire integrity
Connector condition
Vacuum source
Sensor calibration
Software updates
Shared circuits

A PCM is expensive, requires programming on many vehicles, and is rarely impressed by being replaced when a corroded connector was the actual problem.

Unlike a performance code such as P0106, P0108 is primarily an electrical high-input fault. The PCM is receiving a voltage signal that is higher than expected, usually close to the five-volt reference voltage.

The goal of diagnosis is to determine whether that high signal is being caused by:

A failed MAP sensor
An open ground circuit
A signal wire shorted to voltage
Connector damage
Vacuum hose problems
A shared five-volt reference fault
Actual excessive manifold pressure
PCM failure

The following diagnostic process follows the same logical sequence used by professional technicians.

How to Diagnose the P0108 Code

Step 1: Confirm the Code

Connect an OBD-II scan tool and record:

Stored codes
Pending codes
Permanent codes
Freeze-frame data
MAP pressure
MAP voltage
BARO pressure
Engine RPM
Throttle position
Fuel trims
Intake Air Temperature
Battery voltage

Do not erase the code before recording freeze-frame information.

Step 2: Check for Related Trouble Codes

Inspect for additional DTCs involving:

MAP sensor
BARO sensor
MAF sensor
Throttle position
Turbocharger boost
Fuel trims
Reference voltage
Camshaft timing
Misfires

Common related codes include:

P0105
P0106
P0107
P0109
P0172
P0234
P0300
P0641
P0651

Multiple sensor codes often indicate wiring or reference-voltage issues rather than multiple failed sensors.

Step 3: Review Freeze-Frame Data

Determine when the PCM detected the fault.

Review:

Engine load
MAP pressure
Engine speed
Throttle position
Coolant temperature
Vehicle speed
Fuel trims
Battery voltage

If P0108 occurred immediately after startup, inspect the sensor circuit first.

If it occurred during boost, compare commanded and actual manifold pressure.

Step 4: Perform a Visual Inspection

Inspect the entire MAP sensor circuit.

Look for:

Loose connectors
Broken connector locks
Corrosion
Moisture
Oil contamination
Damaged wiring
Pinched harnesses
Melted insulation
Previous repairs
Rodent damage

Many electrical faults become obvious before a multimeter is ever connected.

Step 5: Inspect the Connector

Disconnect the MAP sensor connector.

Inspect for:

Bent terminals
Spread terminals
Corroded pins
Loose terminal tension
Water intrusion
Oil contamination
Damaged seals
Pins pushed backward

Repair connector problems before replacing the sensor.

Step 6: Compare MAP and BARO with the Engine Off

Turn the ignition on without starting the engine.

MAP should be very close to BARO.

Typical atmospheric pressure near sea level is approximately:

95–105 kPa
28–31 inHg
13.8–15.2 psi absolute

Large differences may indicate:

Sensor failure
Wiring fault
BARO fault
PCM issue

Step 7: Start the Engine

Allow the engine to reach operating temperature.

At idle, manifold pressure should decrease significantly compared with key-on readings.

If MAP pressure remains near atmospheric pressure while the engine idles normally, suspect:

Failed sensor
Vacuum hose problem
Blocked sensor port
Open ground
Signal short to voltage

Step 8: Verify the Five-Volt Reference

Using a digital multimeter, verify the sensor receives approximately:

4.8–5.2 volts

If reference voltage is incorrect:

Inspect:

Shared sensors
Harness damage
PCM output
Connector corrosion

Do not replace the MAP sensor until reference voltage has been confirmed.

Step 9: Test the Sensor Ground

Perform a voltage-drop test between sensor ground and battery negative.

Inspect for:

Broken grounds
Corrosion
Loose ground bolts
Damaged splices
Engine ground straps

An open ground frequently causes P0108 because signal voltage rises toward reference voltage.

Step 10: Measure Signal Voltage

Back-probe the signal wire.

Typical values include:

Key On Engine Off: 4.0–4.8 volts
Warm Idle: approximately 1 volt
Heavy acceleration: 3.5–4.5 volts

If voltage remains near five volts during idle, continue testing.

Step 11: Disconnect the MAP Sensor

Turn the ignition off.

Disconnect the sensor.

Turn the ignition back on.

If scan-tool pressure changes dramatically:

The sensor may be internally shorted.

If pressure remains high:

Wiring
PCM
Reference circuits

become more likely.

Step 12: Check for Signal Wire Shorted to Voltage

Disconnect the MAP sensor.

Using the wiring diagram:

Measure voltage on the signal wire.

Unexpected voltage may indicate contact with:

Five-volt reference
Battery voltage
Injector circuits
Alternator wiring
Aftermarket accessories

Repair damaged wiring before replacing the sensor.

Step 13: Test Signal-Wire Continuity

Measure continuity between:

MAP connector
PCM connector

Inspect for:

High resistance
Open circuit
Previous repairs
Corrosion
Damaged terminals

Load testing is often more effective than a simple continuity test.

Step 14: Perform a Wiggle Test

While monitoring scan data, gently move:

MAP connector
Harness
PCM connector
Intake harness
Engine wiring loom

Watch for:

Voltage spikes
Signal dropouts
Engine stumble
Pressure changes

Intermittent harness faults often appear only during movement.

Step 15: Inspect the MAP Port

Remove the sensor if possible.

Inspect for:

Carbon
Oil sludge
Dirt
Moisture
Damaged seals

A blocked sensing port can prevent proper pressure changes from reaching the sensor.

Step 16: Inspect Vacuum Hoses

For remotely mounted MAP sensors inspect:

Vacuum hose
Rubber elbows
Plastic fittings
Restrictors
Cracks
Loose connections

A disconnected hose can leave the sensor exposed to atmospheric pressure, creating a continuously high signal.

Step 17: Compare MAP Data with a Vacuum Gauge

Install a mechanical vacuum gauge.

Compare actual manifold vacuum with scan-tool pressure.

A healthy gasoline engine generally produces approximately:

17–22 inches of mercury at warm idle

If vacuum is normal but MAP pressure remains high, suspect:

Sensor
Wiring
Ground
Vacuum connection

Step 18: Test Sensor Response with a Vacuum Pump

Connect a hand-operated vacuum pump.

Apply vacuum gradually.

The signal voltage should decrease smoothly.

Look for:

Dead spots
Flat lines
Delayed response
Voltage spikes

Replace the sensor if it fails to respond properly.

Step 19: Check Shared Reference Circuits

Many sensors share the same five-volt reference.

Disconnect one shared sensor at a time while monitoring reference voltage.

Possible shared sensors include:

TPS
APP
Fuel pressure sensor
A/C pressure sensor
EGR position sensor

One failed sensor can affect multiple systems simultaneously.

Step 20: Inspect Turbocharger Plumbing

On turbocharged engines inspect:

Charge pipes
Intercooler
Boost hoses
Wastegate hoses
Boost control solenoid
Pressure sensor seals

A true overboost condition can occasionally trigger P0108.

Step 21: Inspect Engine Mechanical Condition

Although uncommon, actual manifold pressure may be elevated because of:

Incorrect valve timing
Burned valves
Low compression
Vacuum leaks
Stuck-open EGR valve

Mechanical problems usually trigger P0106 but should not be ignored.

Step 22: Inspect PCM Connectors

Disconnect battery power if required.

Inspect PCM connectors for:

Moisture
Corrosion
Bent pins
Loose terminals
Previous probing damage

Poor PCM connections can distort sensor voltage.

Step 23: Check Technical Service Bulletins

Search manufacturer service information for:

Updated MAP sensors
Wiring repairs
Calibration updates
Known connector failures
False P0108 detection

Following a TSB may reduce diagnostic time significantly.

Step 24: Verify PCM Operation

If:

Reference voltage
Ground
Signal wire
Sensor
Vacuum source
Connector

all test correctly, evaluate PCM operation.

PCM failure is rare and should be the final possibility considered.

Step 25: Verify the Repair

After repairs:

Clear diagnostic codes.
Start the engine.
Monitor MAP voltage.
Verify idle pressure.
Confirm throttle response.
Complete a road test.
Perform a drive cycle.
Confirm P0108 does not return.

A successful repair restores normal MAP readings under all operating conditions.

Common Repairs for P0108

Typical repairs include:

Replace MAP sensor
Repair signal wire shorted to voltage
Restore sensor ground
Repair connector damage
Replace damaged vacuum hose
Clean MAP sensor port
Repair harness damage
Replace faulty BARO sensor
Repair shared five-volt circuit
Repair turbo boost leaks
Update PCM software
Replace PCM (rare)

P0108 Repair Costs

Repair	Estimated Cost
MAP sensor cleaning	$20–$100
Vacuum hose replacement	$20–$150
Connector repair	$75–$250
Wiring repair	$100–$500
MAP sensor replacement	$120–$450
BARO sensor replacement	$150–$500
Turbo boost repair	$150–$1,000+
PCM software update	$100–$300
PCM replacement/programming	$1,000–$3,500+

Actual costs vary depending on vehicle make, labor rates, and the complexity of the electrical repair.

Common Diagnostic Mistakes

Replacing the MAP Sensor Immediately

Many P0108 cases are caused by:

Open grounds
Wiring faults
Connector corrosion
Vacuum hose issues

Always test the circuit first.

Ignoring Ground Integrity

An open ground commonly creates a high-voltage signal.

Voltage-drop testing is far more useful than checking continuity alone.

Skipping Vacuum Hose Inspection

Remote MAP sensors depend on an unrestricted vacuum source.

A disconnected hose can mimic sensor failure.

Ignoring Shared Five-Volt Circuits

A fault in another sensor may distort MAP readings.

Always inspect shared reference circuits.

Failing to Compare MAP and BARO

With the engine off, MAP and BARO should be nearly identical.

This simple comparison often identifies the problem immediately.

Installing Cheap Aftermarket Sensors

Low-quality sensors frequently produce inaccurate voltage curves.

OEM or premium replacement sensors are strongly recommended.

Condemning the PCM Too Early

PCM failures are uncommon.

Verify every external component before replacing the module.

Manufacturer-Specific Notes

GM

Inspect:

MAP port contamination
PCV leaks
Shared five-volt circuits
Ground junctions

Ford

Inspect:

EcoBoost TMAP sensors
Charge-pipe wiring
Shared pressure circuits
PCM updates

Toyota / Lexus

Use OEM sensors whenever possible.

Check:

Connector fit
BARO correlation
Sensor calibration

Honda / Acura

Inspect:

MAP connector corrosion
Intake manifold vacuum
Valve adjustment
Engine grounds

Nissan / Infiniti

Compare:

MAP
MAF
Throttle Position

Inspect intake boot integrity and harness routing.

Hyundai / Kia

Check:

Shared reference circuits
PCM calibration
MAP connector seals

Volkswagen / Audi

Inspect:

TMAP sensors
Boost plumbing
Intercooler piping
Diverter valves
Moisture intrusion

BMW / MINI

Inspect:

Charge pipes
TMAP sensors
VANOS operation
PCV system

Mercedes-Benz

Inspect:

Pressure sensor seals
Turbo plumbing
Engine harness near hot components

Subaru

Modified engines should verify:

Sensor scaling
MAP calibration
Tune compatibility
Boost control

Chrysler / Dodge / Jeep / Ram

Inspect:

Intake manifold wiring
Shared five-volt circuits
Connector contamination
PCM grounds

Preventative Maintenance

To reduce the risk of future P0108 faults:

Replace damaged vacuum hoses
Repair oil leaks near the sensor
Keep connectors dry
Secure wiring away from heat
Inspect engine grounds
Use OEM-quality MAP sensors
Maintain the charging system
Repair turbo boost leaks promptly
Avoid poor-quality engine tunes
Inspect wiring during major engine service
Replace broken connector locks
Follow manufacturer TSBs

Electrical problems are often easier to prevent than diagnose. Spending five minutes securing a harness today can save five hours chasing an invisible short next month.

Frequently Asked Questions

What does P0108 mean?

P0108 means the PCM has detected a MAP or BARO sensor signal voltage that is higher than the acceptable operating range.

Does P0108 mean the MAP sensor is bad?

No. It may also be caused by:

Open ground
Signal wire shorted to voltage
Connector damage
Vacuum hose problems
PCM issues

Can an open ground cause P0108?

Yes. It is one of the most common electrical causes of this code.

Can a vacuum hose cause P0108?

Yes. A disconnected or blocked hose can keep the sensor at atmospheric pressure, resulting in an artificially high signal.

Can turbo overboost cause P0108?

Yes. A genuine overboost condition can produce MAP readings that exceed the expected range.

Can I drive with P0108?

Short trips may be possible, but avoid driving if the engine stalls, misfires, enters limp mode, or produces heavy black smoke.

What voltage should a MAP sensor produce?

Most analog MAP sensors produce approximately:

4–4.8 volts with the key on and engine off
0.9–1.8 volts at warm idle
3.5–4.5 volts during heavy engine load

Always verify specifications for the vehicle being tested.

What is the difference between P0107 and P0108?

P0107 indicates the signal voltage is too low.

P0108 indicates the signal voltage is too high.

Can clearing the code fix P0108?

No. Clearing the code only removes the warning until the fault occurs again.

How much does it cost to repair P0108?

Repairs range from under $100 for simple wiring or hose repairs to more than $3,000 if PCM replacement is required.

Final Thoughts

The P0108 MAP/Barometric Pressure Circuit High Input code indicates that the PCM is receiving a pressure-sensor voltage that is higher than expected.

While a failed MAP sensor is a common cause, many P0108 repairs involve damaged wiring, poor grounds, disconnected vacuum hoses, connector corrosion, or shared five-volt reference faults.

Professional diagnosis should begin with verifying the sensor’s power, ground, and signal voltage before replacing components. Comparing MAP readings with BARO pressure, checking manifold vacuum, and inspecting the wiring harness often reveals the root cause much faster than replacing parts at random.

The good news is that most P0108 repairs are straightforward once the electrical fault is isolated. The bad news is that electricity has an uncanny ability to hide the real problem in the last place anyone thinks to look.

Related Pro Street Diagnostic Guides

Related MAP Sensor Codes

P0105 Code Explained: MAP/BARO Circuit Malfunction
P0106 Code Explained: MAP/BARO Circuit Range/Performance
P0107 Code Explained: MAP/BARO Circuit Low Input
P0109 Code Explained: MAP/BARO Circuit Intermittent

Related Mass Air Flow Codes

Complete OBD-II Code Libraries

Connect this article to P0105 through P0109 to build a comprehensive MAP/BARO diagnostic cluster and strengthen your topical authority for air-intake and engine-management diagnostics.