Code Definition

P1108 — Dual Alternator upper circuit

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Ford

About P1108

P1108 is a manufacturer-specific powertrain diagnostic trouble code recorded for Ford vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1108 is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1108 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The P1108 code indicates a fault in the upper or primary alternator monitor and control circuit of a Ford dual alternator system. The primary alternator is the main charging source, while the secondary unit adds capacity, and the PCM watches a monitor or communication circuit to confirm the upper unit is connected and responding. This code is set when the PCM sees an electrical problem on that circuit, such as an open, a short, or an implausible signal, rather than a charging output shortfall on its own. Because the upper alternator carries the main charging load, a circuit fault here can lead...

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