P1107
GMDual Alternator Lower Circuit Malfunction/ Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent Low Voltage
Medium SeverityThis code indicates a problem with either the Manifold Absolute Pressure (MAP) sensor circuit experiencing intermittent low voltage, or a malfunction in the lower circuit of a dual alternator system. A faulty MAP sensor can lead to noticeable engine performance issues, while an alternator circuit problem can affect the vehicle's charging system.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is turned off and the parking brake is engaged before performing any inspection or repair. When working with electrical components, always disconnect the negative battery terminal to prevent electrical shock or damage to the vehicle's electrical system. Be cautious of hot engine components and rotating parts.
Common Symptoms
- Check Engine Light illumination
- Rough idle
- Poor engine performance or hesitation during acceleration
- Reduced fuel economy
- Difficulty starting the engine
- Engine stalling
- Battery warning light (if related to alternator)
- Dimming headlights or interior lights (if related to alternator)
Common Causes
- Faulty Manifold Absolute Pressure (MAP) sensor
- Damaged or corroded wiring or connector for the MAP sensor circuit
- Vacuum leak affecting MAP sensor readings
- Loose or corroded battery terminals
- Faulty lower alternator circuit (in dual alternator systems)
- Engine Control Module (ECM) failure (rare)
Frequently reported on: Chevrolet Silverado 1500 (2000-2006), GMC Sierra 1500 (2000-2006), Chevrolet S10 (1998-2004), Pontiac Grand Am (1999-2005), Buick LeSabre (2000-2005)
Diagnostic Steps
- Inspect the electrical connector and wiring for the MAP sensor for any signs of damage, corrosion, or loose connections. Clean or repair as necessary.
- Check all vacuum lines connected to the intake manifold for cracks, leaks, or disconnections. Repair or replace any damaged lines.
- If no obvious wiring or vacuum issues are found, consider testing or replacing the MAP sensor itself. This is often a straightforward replacement.
- For dual alternator systems, visually inspect the alternators and their associated wiring, especially the lower circuit connections, for signs of damage or loose terminals.
- Check the vehicle's battery terminals for corrosion or looseness and clean or tighten them as needed. Ensure the battery itself is in good condition.
👨🔧 When to Call a Professional
If basic diagnostics and replacement of the MAP sensor do not resolve the issue, or if there are clear signs of a charging system problem (like a battery light or dimming lights), it's best to consult a professional. Advanced electrical diagnostics are often required to pinpoint intermittent wiring issues or diagnose dual alternator system faults.
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 sent to the Engine Control Module (ECM) to calculate engine load and adjust fuel delivery and ignition timing, optimizing engine performance and fuel efficiency.
Can I drive with a P1107 code?
While the vehicle might still be drivable, it's not recommended for extended periods. The engine's performance and fuel economy will likely be negatively affected, and ignoring the issue could lead to more significant problems over time.
How do I test a MAP sensor?
A MAP sensor can be tested using a multimeter to check for proper voltage readings at different engine vacuum levels, or by using a vacuum pump to simulate pressure changes. Comparing readings to specifications from a service manual is crucial.
Could a vacuum leak cause P1107?
Yes, a vacuum leak can cause incorrect pressure readings at the MAP sensor, potentially triggering a P1107 code, as it can be interpreted as an intermittent low voltage or incorrect signal by the ECM.
Is P1107 always about the MAP sensor?
While P1107 for GM vehicles often points to the MAP sensor circuit, its definition also includes 'Dual Alternator Lower Circuit Malfunction.' Therefore, it's important to consider both possibilities during diagnosis, especially if the vehicle has a dual alternator system and exhibits charging issues.