P1108 is a manufacturer-specific OBD-II diagnostic trouble code. Because it is manufacturer-specific, its exact definition depends entirely on the vehicle application, ranging from barometric pressure sensor circuits to dual alternator charging system faults.
The exact application must be verified before diagnosis. The code indicates the control module detected an unexpected signal or circuit fault, but testing is required to identify the root cause.
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Key Takeaways
- P1108 is a manufacturer-specific code, meaning its exact definition varies by automaker and vehicle application.
- On GM applications, it typically indicates a BARO to MAP sensor signal comparison fault.
- On Ford and Lincoln applications, it often indicates a dual alternator battery lamp circuit malfunction.
- Diagnosis requires verifying the exact factory definition and testing the relevant sensor or charging circuits.
P1108 Code Description and Implications
P1108 is a manufacturer-specific powertrain code. Because the second digit is “1”, the definition is controlled by the automaker rather than the SAE standardized list.
Some GM and Chevrolet applications: P1108 indicates a BARO to MAP sensor circuit comparison fault, meaning the barometric and manifold absolute pressure readings are outside the expected correlation.
Some Ford, Lincoln, and Mercedes-Benz applications: P1108 indicates a dual alternator battery lamp circuit malfunction, affecting vehicles equipped with two alternators.
Some Honda and Acura applications: P1108 indicates a barometric pressure (BARO) sensor circuit high input fault.
When the control module detects an unexpected signal, it sets this fault code. Because this is a manufacturer-specific code, the exact definition and diagnostic steps vary by automaker.
Common Causes of the P1108 Code
Possible causes depend entirely on the specific vehicle application.
For GM BARO/MAP applications, a failing MAP sensor, a failing internal BARO sensor, damaged wiring, or an intake manifold vacuum leak can trigger the correlation fault.
For Ford and Lincoln dual alternator applications, a failing alternator, damaged wiring in the battery lamp circuit, or a blown fuse can cause the circuit malfunction.
For Honda and Acura BARO applications, a failing BARO sensor, an open or shorted circuit, or a poor electrical connection can cause the high input signal.
Symptoms Associated With P1108
The primary symptom is an illuminated Check Engine Light.
On GM and Honda applications, drivers may experience rough idling, hesitation, poor acceleration, or decreased fuel efficiency due to incorrect air pressure readings affecting the air-fuel mixture.
On Ford and Lincoln dual alternator applications, symptoms may include a battery warning light, dimming electrical components, or a failing charging system.
Diagnosing the P1108 Trouble Code
Diagnosis must begin by confirming the exact factory definition for the specific make, model, and year.
For GM and Honda BARO/MAP applications, technicians monitor live MAP and BARO data, inspect the sensors and wiring, and check for intake vacuum leaks.
For Ford and Lincoln dual alternator applications, technicians test the alternator output, inspect the battery lamp circuit wiring, and verify the condition of the fuses and connections.
Repairing the P1108 Issue
Repairs follow the confirmed diagnosis for the specific application.
If a MAP or BARO sensor fails electrical testing or live data verification, replacing the confirmed failed sensor resolves the pressure reading fault. Repairing damaged wiring or fixing vacuum leaks may also be required.
If a dual alternator or its control circuit fails testing, replacing the alternator or repairing the battery lamp circuit wiring restores proper charging system operation.
Cost Considerations for P1108 Repairs
Repair costs vary depending on the underlying fault and the vehicle application.
Replacing a MAP or BARO sensor involves standard parts and moderate labor. Replacing an alternator on a dual-alternator system requires more labor and expensive parts.
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Prevention Strategies for Future Occurrences
Inspecting exposed wiring and keeping sensor connectors clean can help prevent moisture intrusion and corrosion that lead to circuit faults.
Keeping the intake manifold and vacuum hoses in good condition helps prevent leaks that can skew MAP sensor readings on applicable vehicles.
Troubleshooting Tips and Best Practices
Never assume a manufacturer-specific code has a universal meaning. Always verify the exact factory service information for your specific vehicle.
Do not replace an alternator or PCM without first verifying the wiring, connectors, and live data signals.
If P1108 is accompanied by other MAP or BARO codes, suspect a shared vacuum leak or wiring harness issue rather than multiple simultaneous sensor failures.
More OBD-II Codes
| P1103 | P1104 | P1105 | P1106 |
| P1107 | P1109 | P1111 | P1112 |
| P1114 | P1115 | P1116 | P1117 |
| P0107 | P0108 | P1100 | P1101 |
| P0562 | P0620 | P0622 | P0625 |
| P0100 | P0171 | P0300 | P0420 |
Frequently Asked Questions
Is P1108 a generic OBD-II code?
No. P1108 is a manufacturer-specific code, meaning its exact definition and diagnostic procedure depend entirely on the vehicle’s make, model, and application.
Can I drive my vehicle with a P1108 code?
It depends on the application. If it indicates a failing dual alternator charging system, driving the vehicle can leave you stranded and should be avoided until repaired.
Will a P1108 code cause poor fuel economy?
Yes. On applications where P1108 indicates a BARO or MAP sensor fault, the control module cannot calculate the correct air-fuel mixture, resulting in decreased fuel efficiency.
Does P1108 always mean the sensor or alternator is broken?
No. The code often points to an electrical fault like damaged wiring, a poor connection, or an intake vacuum leak rather than a mechanically failed sensor or alternator.
How do I clear a manufacturer-specific P1108 code?
Clearing the code requires fixing the underlying sensor correlation or charging system fault. Simply using a scan tool to erase the code will not repair the root cause.
What Should You Do About the P1108 Code?
Confirm the exact factory definition for your specific vehicle, then follow the applicable manufacturer diagnostic procedure for the relevant system and components.
Because P1108 is manufacturer-specific, testing the exact BARO/MAP sensors, dual alternator circuits, or wiring identified by the factory service information is required to find the root cause.
Once the fault is confirmed, perform the necessary repairs and verify the fix by clearing the codes and completing a test drive.
