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

The P0108 code indicates that the MAP or BARO sensor circuit is sending voltage above the PCM’s expected maximum.

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:

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

ItemInformation
Diagnostic CodeP0108
Generic DefinitionMAP/BARO Circuit High Input
CategoryPowertrain
SystemAir Intake / Engine Management
Fault TypeHigh Signal Voltage
SeverityModerate to High
Safe to Drive?Sometimes, depending on symptoms
Common CausesFaulty MAP sensor, open ground, signal shorted to voltage
Common SymptomsRough 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:

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:

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:

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:

As intake-manifold pressure changes:

  1. The diaphragm flexes.
  2. Internal resistance changes.
  3. Signal voltage changes.
  4. The PCM converts voltage into pressure.

A typical analog MAP sensor may produce approximately:

Operating ConditionTypical Voltage
Key On, Engine Off4.0–4.8 V
Warm Idle0.9–1.8 V
Light Cruise1.5–2.8 V
Heavy Acceleration3.5–4.5 V
Turbocharged BoostMay 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:

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:

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:

P0108 may set when:

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

P0108 vs P0105, P0106, P0107 and P0109

CodeDescriptionGeneral Fault
P0105MAP/BARO Circuit MalfunctionGeneral circuit fault
P0106MAP/BARO Range/PerformanceImplausible or inaccurate signal
P0107MAP/BARO Circuit Low InputSignal voltage too low
P0108MAP/BARO Circuit High InputSignal voltage too high
P0109MAP/BARO Circuit IntermittentSignal cuts in and out

An easy way to remember the group:

Common Symptoms of P0108

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

Common symptoms include:

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:

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:

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:

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:

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:

A falsely high engine-load signal may result in:

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:

Possible causes on turbocharged vehicles include:

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:

Prompt diagnosis is recommended.

Can You Drive with P0108?

Short-distance driving may be possible if:

Avoid driving if:

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:

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:

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:

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:

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

25 Common Causes of P0108

The most common causes include:

  1. Failed MAP sensor
  2. MAP signal wire shorted to the five-volt reference
  3. MAP signal wire shorted to battery voltage
  4. Open sensor ground circuit
  5. High resistance in the sensor ground
  6. Loose MAP sensor connector
  7. Corroded connector terminals
  8. Bent or spread connector pins
  9. Water intrusion in the connector
  10. Oil contamination in the connector
  11. Damaged wiring harness
  12. Melted wiring near hot engine components
  13. Improper previous wiring repair
  14. Disconnected MAP vacuum hose
  15. Cracked MAP vacuum hose
  16. Blocked or restricted MAP vacuum hose
  17. Restricted MAP sensor port
  18. Faulty BARO sensor
  19. Shared five-volt reference fault
  20. Incorrect aftermarket MAP sensor
  21. Incorrect sensor calibration or tuning
  22. Actual turbocharger overboost condition
  23. Incorrect engine timing
  24. Internal PCM software or calibration fault
  25. 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:

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:

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:

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:

Incorrect Aftermarket Sensor or Tune

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

This is common on:

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:

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:

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:

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:

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

Step 2: Check for Related Trouble Codes

Inspect for additional DTCs involving:

Common related codes include:

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:

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:

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

Step 5: Inspect the Connector

Disconnect the MAP sensor connector.

Inspect for:

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:

Large differences may indicate:

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:

Step 8: Verify the Five-Volt Reference

Using a digital multimeter, verify the sensor receives approximately:

If reference voltage is incorrect:

Inspect:

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:

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:

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:

If pressure remains high:

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:

Repair damaged wiring before replacing the sensor.

Step 13: Test Signal-Wire Continuity

Measure continuity between:

Inspect for:

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

Step 14: Perform a Wiggle Test

While monitoring scan data, gently move:

Watch for:

Intermittent harness faults often appear only during movement.

Step 15: Inspect the MAP Port

Remove the sensor if possible.

Inspect for:

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

Step 16: Inspect Vacuum Hoses

For remotely mounted MAP sensors inspect:

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:

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

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:

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:

One failed sensor can affect multiple systems simultaneously.

Step 20: Inspect Turbocharger Plumbing

On turbocharged engines inspect:

A true overboost condition can occasionally trigger P0108.

Step 21: Inspect Engine Mechanical Condition

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

Mechanical problems usually trigger P0106 but should not be ignored.

Step 22: Inspect PCM Connectors

Disconnect battery power if required.

Inspect PCM connectors for:

Poor PCM connections can distort sensor voltage.

Step 23: Check Technical Service Bulletins

Search manufacturer service information for:

Following a TSB may reduce diagnostic time significantly.

Step 24: Verify PCM Operation

If:

all test correctly, evaluate PCM operation.

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

Step 25: Verify the Repair

After repairs:

  1. Clear diagnostic codes.
  2. Start the engine.
  3. Monitor MAP voltage.
  4. Verify idle pressure.
  5. Confirm throttle response.
  6. Complete a road test.
  7. Perform a drive cycle.
  8. Confirm P0108 does not return.

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

Common Repairs for P0108

Typical repairs include:

P0108 Repair Costs

RepairEstimated 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:

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:

Ford

Inspect:

Toyota / Lexus

Use OEM sensors whenever possible.

Check:

Honda / Acura

Inspect:

Nissan / Infiniti

Compare:

Inspect intake boot integrity and harness routing.

Hyundai / Kia

Check:

Volkswagen / Audi

Inspect:

BMW / MINI

Inspect:

Mercedes-Benz

Inspect:

Subaru

Modified engines should verify:

Chrysler / Dodge / Jeep / Ram

Inspect:

Preventative Maintenance

To reduce the risk of future P0108 faults:

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:

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:

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

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.

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