P0107 MAP / BARO Sensor Circuit Low Input

The P0107 trouble code means the engine control module (ECM/PCM) has detected a lower-than-expected voltage signal from the MAP/BARO sensor circuit.

The MAP sensor provides the ECU with information about pressure in the intake manifold. This information is used to calculate engine load and to help determine the appropriate amount of fuel and ignition timing.

When the electrical signal from the sensor falls below the expected range, the ECU can store P0107 and illuminate the Check Engine Light.

What Does “Low Input” Mean?

“Low input” refers to the electrical signal reaching the ECU, not necessarily low intake pressure.

This distinction is important.

A low MAP signal can occur because the intake manifold really has a pressure condition that produces a low sensor output, but it can also happen because of an electrical fault.

Possible electrical causes include:

• Signal wire shorted to ground

• Faulty MAP sensor

• Poor sensor ground

• Incorrect sensor power supply

• Damaged wiring

• Corroded connector

• Loose terminal

• Internal sensor failure

Therefore, P0107 should not automatically be treated as proof that the MAP sensor needs to be replaced.

How the MAP Sensor Works

The MAP sensor measures absolute pressure inside the intake manifold.

The ECU uses this information together with other parameters such as:

• Engine RPM

• Throttle position

• Intake air temperature

• Engine coolant temperature

• MAF readings, if equipped

• Fuel trims

At idle, a naturally aspirated engine normally has substantially lower intake-manifold pressure than atmospheric pressure because the closed or partially closed throttle restricts airflow.

As the throttle opens and engine load increases, manifold pressure generally rises.

The MAP sensor converts these pressure changes into an electrical signal that the ECU can interpret.

Common Symptoms of P0107

The symptoms can vary considerably depending on the vehicle and the severity of the fault.

Possible symptoms include:

• Check Engine Light

• Rough idle

• Engine hesitation

• Poor acceleration

• Reduced engine power

• Difficult starting

• Engine stalling

• Increased fuel consumption

• Poor throttle response

• Unstable engine operation

• Abnormal emissions

Some vehicles may continue to drive almost normally despite storing P0107.

Common Causes

Faulty MAP sensor

The pressure-sensing element can fail internally and produce a signal that is lower than expected.

Signal wire shorted to ground

This is an important possibility with a low-input code.

If the MAP signal wire contacts ground, the ECU can see a very low voltage regardless of the actual intake pressure.

Poor sensor ground

A damaged or corroded ground/return circuit can interfere with the sensor's output.

Incorrect sensor power supply

If the sensor does not receive the required supply voltage, its signal may not be correct.

Damaged wiring

The harness may be:

• Broken

• Chafed

• Melted

• Pinched

• Corroded internally

• Previously repaired incorrectly

Connector problems

Loose terminals, corrosion or moisture can cause an unreliable MAP signal.

Blocked MAP sensor port

On some engines, contamination around the sensor's pressure passage can interfere with pressure measurement.

Actual intake-pressure problem

A genuine pressure condition can also influence the sensor signal, although the circuit should be tested before assuming that the engine's mechanical condition is responsible.

Start With the Electrical System

Because P0107 specifically identifies a low input signal, the electrical circuit should be checked early in the diagnostic process.

Using the vehicle's wiring diagram, identify the MAP sensor's:

• Power supply

• Ground/return

• Signal circuit

The exact configuration varies between vehicles.

Check that the sensor receives the correct supply voltage and that the ground circuit is reliable.

Check the MAP Signal

The signal should be checked under several conditions rather than at only one moment.

Useful conditions include:

• Ignition on, engine off

• Engine idling

• Light acceleration

• Rapid throttle opening

• Deceleration

With the engine off and ignition on, the MAP reading should generally correspond reasonably closely to atmospheric pressure.

Once the engine starts, manifold pressure should change according to engine operating conditions.

A signal that remains extremely low despite clear changes in engine load is suspicious.

Inspect the Wiring Carefully

The MAP sensor harness should be physically inspected.

Look for:

• Damaged insulation

• Broken conductors

• Chafing

• Melted sections

• Oil contamination

• Corrosion

• Poor previous repairs

• Loose connectors

Pay particular attention to areas where the wiring passes near the engine, throttle body, intake manifold or hot components.

A wire can look intact externally while being damaged internally.

Check for a Short to Ground

A short to ground is particularly relevant to a low-input MAP code.

If the signal circuit is being pulled toward ground, the ECU may interpret the MAP signal as abnormally low.

With the sensor disconnected and the appropriate testing procedure from the vehicle manufacturer, the signal circuit can be checked for unwanted continuity to ground.

The test should be performed according to the vehicle's wiring specifications because some circuits contain additional electronics that can affect measurements.

Inspect the MAP Sensor Port

If the sensor is mounted directly to the intake manifold, inspect the pressure passage when appropriate.

Look for:

• Oil deposits

• Carbon buildup

• Dirt

• Moisture

• Other contamination

A restricted pressure passage can prevent the sensor from accurately detecting manifold pressure.

Do not automatically spray aggressive solvents onto the sensing element. MAP sensors contain delicate electronic components, and cleaning procedures vary by manufacturer.

Could a Vacuum Leak Cause P0107?

A vacuum leak changes intake-manifold pressure, so it can influence MAP readings.

However, a vacuum leak does not automatically mean the MAP circuit has a low electrical input.

If the sensor is correctly reporting the pressure change, the MAP sensor itself may be functioning normally.

This is why live data and electrical testing should be considered together.

Could the Throttle Body Cause P0107?

The throttle controls the amount of air entering the engine and therefore has a direct influence on manifold pressure.

A throttle-body problem can produce unusual MAP readings.

Possible throttle-related issues include:

• Incorrect throttle position

• Sticking throttle plate

• Electronic throttle malfunction

• Airflow restriction

• Throttle-position sensor problems

If throttle-related codes are also stored, the throttle system should be investigated.

Can a MAF Sensor Cause P0107?

A faulty MAF sensor can create discrepancies between measured airflow and manifold pressure.

However, a MAF problem does not automatically explain a low MAP electrical signal.

If the MAP voltage itself is below specification, the MAP circuit should be tested directly.

The MAF and MAP sensors can then be compared through live data to determine whether the readings make sense together.

Diagnosing P0107 With a Scan Tool

A scan tool can provide useful information before any parts are replaced.

Monitor:

• MAP pressure

• MAP voltage, if available

• Engine RPM

• Throttle position

• Engine load

• MAF

• Fuel trims

• Coolant temperature

• Intake air temperature

Watch for a MAP reading that remains abnormally low or does not respond appropriately when engine load changes.

If the scan tool shows a very low MAP signal while direct electrical measurements show that the sensor is receiving the correct supply and producing the expected output, communication or ECU-side issues may need further investigation.

What About the BARO Reading?

Some vehicles use the MAP sensor to establish or help calculate barometric pressure.

With the engine off and ignition on, the pressure value should generally be reasonably close to the current atmospheric pressure, taking altitude and weather conditions into account.

A completely implausible reading can provide an important clue.

However, atmospheric pressure varies with:

• Altitude

• Weather

• Temperature

Therefore, a small difference from a reference weather-station value does not automatically indicate a fault.

Is the MAP Sensor Usually the Problem?

It can be, but replacing it without testing the circuit can waste time and money.

The MAP sensor becomes a strong suspect when:

• Supply voltage is correct

• Ground/return is correct

• Signal wiring is intact

• There is no short to ground

• Connector terminals are good

• Intake pressure is behaving normally

• The sensor output remains outside specification

In that situation, sensor replacement may be justified.

When Wiring Is the Real Problem

If the sensor itself produces an appropriate signal but the ECU receives a low signal, the problem is likely between the sensor and ECU.

Possible causes include:

• Signal-wire resistance

• Partial wire break

• Short to ground

• Poor connector terminal contact

• Corrosion

• Damaged ECU connector

This is why measuring the signal at both ends of the circuit can be useful.

Don't Rely Only on Continuity Testing

Continuity testing can confirm that a wire is not completely open, but it does not necessarily prove that the circuit can carry a reliable signal under real operating conditions.

A damaged wire can pass a basic continuity test and still develop problems when:

• The engine vibrates

• The harness moves

• Temperature rises

• The circuit is loaded

Voltage-drop testing and signal measurement can provide much more useful information.

Is P0107 Serious?

P0107 is generally not an indication of immediate catastrophic engine damage.

However, an incorrect MAP signal can significantly affect engine control.

The vehicle may experience poor acceleration, unstable operation, increased fuel consumption or stalling.

If the engine is losing power or stalling in traffic, the fault should be addressed promptly because the resulting drivability problem can create a safety issue.

Repairing P0107

The correct repair depends on the diagnosis.

Possible repairs include:

• Replacing a defective MAP sensor

• Repairing the MAP signal wire

• Repairing a short to ground

• Repairing the sensor ground circuit

• Repairing the sensor power supply

• Replacing damaged connector terminals

• Repairing a blocked or contaminated pressure passage

• Correcting an intake-system problem

• Repairing a throttle-related fault

• Repairing an ECU connector or circuit if testing confirms a problem

After the repair, clear the code and test the vehicle under different operating conditions.

Final Takeaway

P0107 means the ECU has detected a MAP/BARO sensor circuit input that is lower than expected.

The most important thing to remember is that “low input” does not automatically mean “bad MAP sensor.”

A shorted signal wire, poor ground, damaged connector, incorrect power supply or wiring fault can produce exactly the same diagnostic code.

A proper diagnosis should therefore begin with the MAP signal, power, ground and wiring, followed by checking whether the actual intake pressure agrees with what the sensor is reporting.