What are the common causes of the P0108 code on a Mercedes-benz?

cause_map_sensor, cause_wiring_damage, cause_connector_corrosion, cause_vacuum_leak

How much does it cost to fix the P0108 code?

The estimated repair cost for the P0108 code is $75 - $300. This includes parts and labor.

P0108Mercedes-benz C-classAnnées: 1996 - 2026

MAP/Barometric Pressure Circuit High Input

Vérifié par un technicien certifié ASE

Est-il sûr de conduire ?Driving with a P0108 code indicates the engine's computer is receiving an incorrect, abnormally high pressure reading from the MAP sensor. This leads the PCM to believe the engine is under a higher load (less vacuum) than it actually is. Consequently, the PCM will likely command an overly rich fuel mixture and potentially alter ignition timing. This can result in symptoms such as reduced engine power, poor fuel economy, rough idle, stalling, and increased exhaust emissions. Prolonged operation with an incorrect air/fuel mixture can lead to premature failure of the catalytic converter, oxygen sensors, and spark plugs. While the vehicle may still be drivable, it is advisable to diagnose and repair this issue promptly to prevent further, more costly damage and ensure safe, reliable operation.

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Qu'est-ce que cela signifie ?

Code P0108 indicates the MAP sensor is sending an abnormally high voltage to the PCM, suggesting lower vacuum than expected.

Avertissement : Ce code de diagnostic fait partie du système OBD2 standard et peut s'appliquer aux modèles Mercedes-benz C-class fabriqués de 1996 à 2026. Cependant, veuillez noter que la présence de ce code dépend de la configuration exacte du moteur, des options et de l'année de production.

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Causes courantes

Capteur MAP (pression absolue du collecteur) défectueux

Faisceau de câblage endommagé ou cassé

Connecteur électrique corrodé ou desserré

Fuite de vide dans le système d'admission

Symptômes à surveiller

Le voyant moteur est allumé
Ralenti irrégulier ou instable
Consommation de carburant accrue
Accélération faible ou réponse lente

Comment Diagnostiquer

**Step 1: Comprehensive Visual Inspection and Vacuum System Integrity Check.** Begin by thoroughly inspecting the MAP sensor's electrical connector for any signs of corrosion, bent pins, or loose connections. Trace the vacuum line from the MAP sensor to the intake manifold, meticulously checking for cracks, kinks, disconnections, or collapsed sections. A significant vacuum leak anywhere in the intake manifold or associated vacuum lines (e.g., PCV system, brake booster) can cause the MAP sensor to report a higher pressure (lower vacuum) than actual, triggering P0108. With the engine off, disconnect the vacuum line from the MAP sensor and apply a known vacuum source (e.g., a hand vacuum pump) directly to the sensor port. Monitor the sensor's voltage output with a multimeter or scan tool; a healthy sensor should show a smooth, proportional decrease in voltage as vacuum increases.

**Step 2: MAP Sensor Electrical Signal Verification with Scan Tool and Multimeter.** Connect a professional scan tool and access live data for the MAP sensor. With the key on, engine off (KOEO), the MAP sensor reading should be close to the current barometric pressure (typically 14.7 PSI or 29.92 inHg at sea level, adjusting for altitude). Start the engine and allow it to idle. A healthy engine at idle should exhibit a MAP reading of approximately 8-10 PSI absolute pressure (or 17-22 inHg of vacuum). If the scan tool consistently reports a pressure significantly higher than expected at idle (e.g., 12-14 PSI or more), it confirms the 'high input' condition. Further, back-probe the MAP sensor's signal wire with a multimeter. At KOEO, expect approximately 4.5-5.0V. At idle, this voltage should drop to around 1.0-1.5V. If the voltage remains high (e.g., above 4.0V) at idle, the sensor or its circuit is faulty.

**Step 3: Wiring Harness and Connector Integrity Test.** With the ignition off, disconnect the MAP sensor connector. Using a multimeter, verify the 5-volt reference voltage supply to the sensor at the appropriate pin on the connector. Then, check for a solid ground connection at the ground pin. Finally, perform a continuity test on the signal wire between the MAP sensor connector and the Powertrain Control Module (PCM) connector. Look for any open circuits, shorts to voltage, or shorts to ground within the harness. Pay particular attention to areas where the wiring may be exposed to heat, vibration, or chafing. Inspect the connector terminals themselves for corrosion, damage, or improper seating.

**Step 4: PCM Input Verification (Advanced Diagnostics).** If the MAP sensor tests good, the vacuum system is confirmed to be leak-free, and the wiring harness integrity is verified, the issue may lie within the PCM's ability to correctly interpret the MAP sensor signal. This is less common but should not be overlooked. Using a breakout box connected to the PCM, directly measure the MAP sensor signal voltage at the PCM input pin while the engine is running. Compare this reading to the live data reported by the scan tool. Any significant discrepancy between the direct measurement at the PCM and the scan tool's reported value could indicate an internal PCM fault, requiring further specialized diagnostics or replacement.

Solutions Courantes

**Replace the Manifold Absolute Pressure (MAP) Sensor:** If diagnostic steps confirm the sensor itself is faulty, consistently sending an abnormally high voltage signal to the PCM, replacing it with a quality OEM or equivalent aftermarket sensor is the primary solution.

**Repair Vacuum Leaks:** Thoroughly inspect and repair any vacuum leaks found in the intake manifold, vacuum lines, PCV system components, or the brake booster. Even a small leak can significantly affect manifold vacuum, causing the MAP sensor to report higher pressure.

**Repair Wiring Harness or Connector:** Address any identified issues with the MAP sensor's electrical circuit, including repairing open circuits, shorts to voltage or ground, or replacing corroded/damaged connectors and terminals. Ensure all connections are clean, tight, and secure.

**Replace Powertrain Control Module (PCM):** In rare instances, after exhaustive testing confirms the MAP sensor, vacuum system, and wiring are all functioning correctly, the PCM itself may be faulty and unable to properly process the MAP sensor's input. This should be a last resort, as PCM replacement is costly and often requires reprogramming.

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Estimation de réparation

$75 - $300

Pièces$30 - $150 (for MAP sensor; additional $10 - $50 for vacuum lines/gaskets if needed)

Main-d'œuvre$120 - $250 (for diagnosis, 1-2 hours); $60 - $180 (for MAP sensor replacement, 0.5-1.5 hours); $120 - $500+ (for vacuum leak repair, highly variable, 1-4+ hours)

Difficulté de réparation (DIY)

Modéré

Autres codes Mercedes-benz populaires

P0120 P0125 P0101

MAP/Barometric Pressure Circuit High Input

Vérifié par un technicien certifié ASE

Qu'est-ce que cela signifie ?

Code P0108 indicates the MAP sensor is sending an abnormally high voltage to the PCM, suggesting lower vacuum than expected.

Comment Diagnostiquer

Solutions Courantes

Qu'est-ce que cela signifie ?

Causes courantes

Symptômes à surveiller

Comment Diagnostiquer

Solutions Courantes

Join the Discussion

Estimation de réparation

Difficulté de réparation (DIY)

Autres codes Mercedes-benz populaires

Scanning Engine...

Qu'est-ce que cela signifie ?

Causes courantes

Symptômes à surveiller

Comment Diagnostiquer

Solutions Courantes

Join the Discussion

Estimation de réparation

Difficulté de réparation (DIY)

Autres codes Mercedes-benz populaires