P1108 - BARO to MAP Sensor Comparison Too High

Introduction:

The P1108 diagnostic trouble code (DTC) signals an issue related to the comparison between the Barometric Pressure (BARO) sensor and the Manifold Absolute Pressure (MAP) sensor readings in your vehicle's engine control system. This discrepancy can indicate a fault with either sensor, the wiring connecting them to the Engine Control Module (ECM), or even vacuum leaks affecting the MAP sensor's readings. Addressing this code promptly is crucial for maintaining optimal engine performance and fuel efficiency.

Comprehensive Table: P1108 - BARO to MAP Sensor

Category	Description	Possible Solutions
Sensor Function	BARO Sensor: Measures atmospheric pressure. Used to adjust fuel delivery based on altitude and weather conditions. MAP Sensor: Measures the pressure inside the intake manifold. Reflects engine load and vacuum.	N/A - This section clarifies the function of each sensor.
Common Symptoms	Poor fuel economy, rough idling, stalling, reduced engine power, check engine light illuminated, hard starting. These symptoms arise from the ECM's inaccurate data about engine load and atmospheric conditions, leading to incorrect fuel mixture calculations.	Address underlying causes based on diagnostic findings. Correct sensor malfunctions or vacuum leaks.
Potential Causes	Faulty BARO sensor, faulty MAP sensor, vacuum leaks affecting MAP sensor readings, wiring issues (damaged, corroded, or shorted wires) in the BARO or MAP sensor circuits, ECM failure (rare), clogged or restricted MAP sensor vacuum line (if applicable), incorrect sensor installation (e.g., wrong sensor type), extreme altitude changes without ECM adaptation.	Diagnose and repair or replace faulty components. Repair wiring issues. Address vacuum leaks. Consider ECM reprogramming or replacement as a last resort.
Diagnostic Steps	1. Scan for other DTCs. Address any other codes first. 2. Visually inspect BARO and MAP sensors and their wiring. 3. Check for vacuum leaks using a smoke machine or carburetor cleaner spray (use caution). 4. Use a multimeter to test BARO and MAP sensor voltage and resistance. 5. Compare BARO and MAP sensor readings using a scan tool. Readings should be close at key-on, engine-off. 6. Perform a MAP sensor vacuum test (if applicable). 7. Check the BARO sensor's reference voltage.	Follow diagnostic procedures systematically. Prioritize basic checks (visual inspection, vacuum leaks) before advanced testing (multimeter, scan tool).
Sensor Location	BARO Sensor: Typically located on the intake manifold, firewall, or inside the ECM. MAP Sensor: Usually mounted on the intake manifold or near the throttle body. Consult your vehicle's repair manual for specific locations.	Refer to vehicle-specific repair manual for precise location.
Sensor Types	BARO Sensor: Typically a piezoelectric sensor. MAP Sensor: Can be piezoelectric or capacitive. Piezoelectric sensors generate voltage based on pressure, while capacitive sensors change capacitance.	Understand the type of sensor used in your vehicle for accurate testing and replacement.
Wiring Diagram Importance	Crucial for identifying correct wires for testing voltage, ground, and signal. Avoids misdiagnosis and potential damage to the ECM. Shows the pinout configuration for both sensors.	Always consult the vehicle-specific wiring diagram before performing any electrical testing.
Vacuum Leaks & MAP	Vacuum leaks cause the MAP sensor to read higher than expected, as it is measuring the pressure differential caused by the leak in addition to the normal manifold pressure. This discrepancy contributes to the P1108 code. Larger leaks have a more significant impact.	Thoroughly inspect for vacuum leaks around the intake manifold, vacuum lines, and throttle body.
Altitude Effects	BARO sensor readings change with altitude. The ECM compensates for altitude changes by adjusting fuel delivery. Rapid altitude changes can sometimes trigger the P1108 code if the BARO and MAP readings haven't stabilized.	Consider recent altitude changes when diagnosing the code. Allow the ECM time to adapt after significant altitude changes.
Scan Tool Data	Use a scan tool to monitor BARO and MAP sensor readings in real-time. Compare readings at key-on, engine-off. MAP reading should be close to BARO reading at key-on, engine-off (atmospheric pressure). Check for erratic or inconsistent readings. Look for sensor data that falls outside the expected range.	Utilize scan tool data effectively to pinpoint the faulty sensor or identify vacuum leaks.
ECM Adaptation	The ECM learns and adapts to sensor variations over time. Resetting the ECM (clearing adaptive memory) can sometimes resolve the P1108 code, especially after replacing a sensor. However, this is not a guaranteed fix and should be done after addressing the root cause.	Consider ECM reset after addressing the underlying cause, but don't rely on it as the primary solution.
Sensor Replacement	If a sensor is determined to be faulty, replace it with a high-quality, OEM-specified replacement. Aftermarket sensors may not meet the same specifications and can cause further issues. Proper installation is critical.	Use OEM or equivalent quality sensors for replacement. Follow proper installation procedures.
Wiring Inspection	Carefully inspect the wiring harness and connectors for the BARO and MAP sensors. Look for signs of damage, corrosion, or loose connections. Check for chafing or rubbing against other components. Use a multimeter to check for continuity and shorts in the wiring.	Thoroughly inspect wiring and connectors for any signs of damage or corrosion. Repair or replace as needed.
Reference Voltage	The BARO sensor typically receives a 5-volt reference voltage from the ECM. Use a multimeter to verify the presence of this voltage at the sensor connector. A missing or incorrect reference voltage indicates a wiring issue or a faulty ECM.	Verify the reference voltage at the BARO sensor connector.
MAP Sensor Vacuum Test (if applicable)	Some MAP sensors have a vacuum line connected to the intake manifold. Disconnect the vacuum line and use a hand-held vacuum pump to apply vacuum to the sensor. Monitor the sensor reading with a scan tool. The reading should change in response to the applied vacuum. A faulty sensor will not respond correctly.	Perform a MAP sensor vacuum test to verify sensor functionality.

Detailed Explanations:

Sensor Function:

BARO Sensor: The Barometric Pressure (BARO) sensor measures the atmospheric pressure surrounding the vehicle. This information is crucial for the ECM to adjust the air-fuel mixture, particularly when the vehicle operates at different altitudes. Lower atmospheric pressure at higher altitudes requires less fuel.
MAP Sensor: The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold. This pressure is directly related to engine load; a lower pressure indicates a higher engine load (more vacuum), requiring more fuel.

Common Symptoms:

The symptoms associated with the P1108 code often stem from the ECM receiving incorrect data about engine load and atmospheric conditions. This leads to an improperly calculated air-fuel mixture, resulting in:

Poor fuel economy: Inaccurate fuel delivery wastes fuel.
Rough idling: The engine struggles to maintain a stable idle speed due to an incorrect air-fuel mixture.
Stalling: The engine may stall, especially at idle or low speeds, due to a lean or rich mixture.
Reduced engine power: The engine may lack power, especially during acceleration, because the air-fuel mixture isn't optimized for the current load.
Check engine light illuminated: The ECM detects the discrepancy between the BARO and MAP sensor readings and illuminates the check engine light.
Hard starting: The engine may be difficult to start due to an incorrect air-fuel mixture.

Potential Causes:

Several factors can contribute to the P1108 code:

Faulty BARO sensor: The BARO sensor may be providing inaccurate readings or no reading at all.
Faulty MAP sensor: Similar to the BARO sensor, the MAP sensor may be malfunctioning and providing incorrect data.
Vacuum leaks affecting MAP sensor readings: Vacuum leaks can cause the MAP sensor to read higher than expected, creating a discrepancy with the BARO sensor.
Wiring issues: Damaged, corroded, or shorted wires in the BARO or MAP sensor circuits can disrupt the signal flow to the ECM.
ECM failure: Although rare, a faulty ECM can misinterpret sensor data or fail to process it correctly.
Clogged or restricted MAP sensor vacuum line (if applicable): A clogged vacuum line can prevent the MAP sensor from accurately measuring manifold pressure.
Incorrect sensor installation (e.g., wrong sensor type): Using the wrong type of sensor or installing it incorrectly can lead to inaccurate readings.
Extreme altitude changes without ECM adaptation: Rapid changes in altitude can sometimes trigger the code if the ECM hasn't had time to adjust.

Diagnostic Steps:

A systematic approach is essential for diagnosing the P1108 code:

Scan for other DTCs: Address any other codes first, as they may be related to the P1108 code.
Visually inspect BARO and MAP sensors and their wiring: Look for any obvious signs of damage, corrosion, or loose connections.
Check for vacuum leaks: Use a smoke machine or carburetor cleaner spray (use caution!) to identify vacuum leaks around the intake manifold, vacuum lines, and throttle body.
Use a multimeter to test BARO and MAP sensor voltage and resistance: Check for proper voltage and resistance readings at the sensor connectors. Consult your vehicle's repair manual for specific values.
Compare BARO and MAP sensor readings using a scan tool: Compare the readings at key-on, engine-off. They should be close to each other (atmospheric pressure).
Perform a MAP sensor vacuum test (if applicable): If the MAP sensor has a vacuum line, use a hand-held vacuum pump to apply vacuum and monitor the sensor reading.
Check the BARO sensor's reference voltage: Verify the presence of a 5-volt reference voltage at the BARO sensor connector.

Sensor Location:

BARO Sensor: The BARO sensor is typically located on the intake manifold, firewall, or even inside the ECM. Consult your vehicle's repair manual for the exact location.
MAP Sensor: The MAP sensor is usually mounted on the intake manifold or near the throttle body. Again, refer to your vehicle's repair manual for specific details.

Sensor Types:

BARO Sensor: Typically a piezoelectric sensor.
MAP Sensor: Can be either piezoelectric or capacitive. Piezoelectric sensors generate voltage based on pressure, while capacitive sensors change capacitance.

Wiring Diagram Importance:

A wiring diagram is crucial for identifying the correct wires for testing voltage, ground, and signal. It helps prevent misdiagnosis and potential damage to the ECM. The diagram shows the pinout configuration for both sensors.

Vacuum Leaks & MAP:

Vacuum leaks cause the MAP sensor to read higher than expected. The sensor measures the pressure differential caused by the leak, in addition to the normal manifold pressure. Larger leaks have a more significant impact on the MAP sensor reading.

Altitude Effects:

BARO sensor readings change with altitude. The ECM compensates for these changes by adjusting fuel delivery. Rapid altitude changes can sometimes trigger the P1108 code if the BARO and MAP readings haven't stabilized.

Scan Tool Data:

Use a scan tool to monitor BARO and MAP sensor readings in real-time. Compare readings at key-on, engine-off. MAP reading should be close to BARO reading at key-on, engine-off (atmospheric pressure). Look for erratic or inconsistent readings.

ECM Adaptation:

The ECM learns and adapts to sensor variations over time. Resetting the ECM (clearing adaptive memory) can sometimes resolve the P1108 code, especially after replacing a sensor. However, this is not a guaranteed fix and should be done after addressing the root cause.

Sensor Replacement:

If a sensor is determined to be faulty, replace it with a high-quality, OEM-specified replacement. Aftermarket sensors may not meet the same specifications and can cause further issues. Proper installation is critical.

Wiring Inspection:

Carefully inspect the wiring harness and connectors for the BARO and MAP sensors. Look for signs of damage, corrosion, or loose connections. Check for chafing or rubbing against other components. Use a multimeter to check for continuity and shorts in the wiring.

Reference Voltage:

The BARO sensor typically receives a 5-volt reference voltage from the ECM. Use a multimeter to verify the presence of this voltage at the sensor connector. A missing or incorrect reference voltage indicates a wiring issue or a faulty ECM.

MAP Sensor Vacuum Test (if applicable):

Some MAP sensors have a vacuum line connected to the intake manifold. Disconnect the vacuum line and use a hand-held vacuum pump to apply vacuum to the sensor. Monitor the sensor reading with a scan tool. The reading should change in response to the applied vacuum. A faulty sensor will not respond correctly.

Frequently Asked Questions:

What does the P1108 code mean? The P1108 code indicates a discrepancy between the readings of the BARO and MAP sensors, suggesting a potential fault in either sensor or related systems.
Can a vacuum leak cause the P1108 code? Yes, vacuum leaks can cause the MAP sensor to read higher than expected, leading to a discrepancy with the BARO sensor and triggering the P1108 code.
How do I test a MAP sensor? You can test a MAP sensor using a multimeter to check its voltage and resistance, or with a scan tool to monitor its readings in real-time. A vacuum pump can also be used to test its response to varying vacuum levels.
Is it safe to drive with a P1108 code? While it might be possible to drive with a P1108 code, it's not recommended as it can lead to poor fuel economy, rough idling, and potential engine damage. It's best to address the issue as soon as possible.
Can I fix the P1108 code myself? Depending on your mechanical skills and experience, you may be able to diagnose and fix the P1108 code yourself. However, it's crucial to follow proper diagnostic procedures and consult your vehicle's repair manual.

Conclusion:

The P1108 code signifies a mismatch between the BARO and MAP sensor readings, which can stem from various causes, including faulty sensors, vacuum leaks, and wiring issues. A systematic diagnostic approach, combined with thorough inspection and testing, is crucial for accurately identifying and resolving the underlying problem, ensuring optimal engine performance and fuel efficiency.