P1107
BMWDual Alternator Lower Circuit Malfunction/ Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent Low Voltage
Medium SeverityThis code indicates either an issue with the electrical circuit of a dual alternator system, specifically a lower voltage malfunction, or an intermittent low voltage reading from the Manifold Absolute Pressure (MAP) sensor. Both conditions can lead to poor engine performance, reduced fuel economy, or charging system problems.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before working on electrical components, especially alternators, to prevent electrical shocks or short circuits. Allow the engine to cool before working on sensors near hot engine parts.
Common Symptoms
- Check Engine Light illumination
- Reduced engine performance or power
- Rough idle or stalling
- Poor fuel economy
- Engine hesitation or misfires
- Battery warning light (if related to alternator circuit)
- Dimming lights or electrical accessory malfunctions (if related to alternator circuit)
Common Causes
- Faulty MAP sensor
- Damaged or corroded wiring in the MAP sensor circuit
- Loose or corroded MAP sensor electrical connector
- Vacuum leaks affecting MAP sensor readings
- Faulty secondary alternator or its control circuit (for dual alternator systems)
- Wiring harness damage or corrosion in the dual alternator lower circuit
- Engine Control Unit (ECU) malfunction (less common)
Frequently reported on: BMW 3-Series (E46) 2001-2006, BMW 5-Series (E39) 1999-2003, BMW X5 (E53) 2000-2006, BMW Z4 (E85) 2003-2008
Diagnostic Steps
- Visually inspect the MAP sensor and its electrical connector for any damage, corrosion, or loose connections.
- Check the wiring harness leading to the MAP sensor for cuts, chafing, or signs of heat damage.
- Verify that all vacuum lines connected to the intake manifold (if applicable for MAP sensor) are intact and free of leaks.
- If comfortable and equipped, use a multimeter to check for proper voltage signals at the MAP sensor connector according to your vehicle's service manual specifications.
- For dual alternator systems, visually inspect the wiring, connections, and belt tension around both alternators.
👨🔧 When to Call a Professional
If after inspecting wiring and testing the MAP sensor the issue persists, or if symptoms strongly point towards a charging system failure that is beyond basic checks, it is best to consult a professional for advanced electrical diagnostics.
Commonly Asked Questions
What is a MAP sensor and what does it do?
The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold. This data is crucial for the engine's computer to calculate air density and adjust fuel delivery and ignition timing.
Can I drive with a P1107 code?
While you might be able to drive, it's not recommended. A faulty MAP sensor can cause significant poor engine performance and fuel economy. If the issue is related to the charging system, it could lead to your vehicle breaking down unexpectedly due to a dead battery.
How do I test a MAP sensor?
You can test a MAP sensor using a multimeter to check its voltage output at different vacuum levels. Consult your vehicle's service manual for specific voltage ranges and testing procedures, and ensure the engine is off before disconnecting any components.
What if my BMW doesn't have a dual alternator system?
For many BMW models, the P1107 code primarily refers to the MAP sensor circuit issue. If your vehicle is not equipped with a dual alternator, you should focus your diagnostic efforts on the MAP sensor and its associated wiring.
Is a P1107 an expensive repair?
Replacing a MAP sensor is generally a moderately priced repair, typically involving the cost of the sensor itself and some labor. However, diagnosing an intermittent electrical issue or a dual alternator fault can be more complex and potentially more costly.