Faulty upper alternator voltage regulator; Open or shorted wiring in the upper alternator control circuit; Corroded or loose electrical connectors at the upper alternator; Failed powertrain control module (PCM) driver circuit; Poor ground connection for the upper alternator

DTC codes / Ford codes / P1105

P1105 · FordDual Alternator Upper Fault

Q: What does code P1105 mean?

Dual Alternator Upper Fault. P1105 on Ford vehicles indicates that the powertrain control module (PCM) has detected a fault in the upper control circuit of the dual alternator system, which is used on models equipped with two alternators to handle high electrical loads. The PCM monitors the upper alternator's regulator circuit and sets this code when the signal voltage is out of range or the circuit is open or shorted.

P1105 on Ford vehicles indicates that the powertrain control module (PCM) has detected a fault in the upper control circuit of the dual alternator system, which is used on models equipped with two alternators to handle high electrical loads. The PCM monitors the upper alternator's regulator circuit and sets this code when the signal voltage is out of range or the circuit is open or shorted.

SystemPowertrain

Code typeFord specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Battery warning light illuminated on the dashboard
Electrical accessories such as lights or radio dimming or flickering
Battery frequently discharging or going dead
Voltage gauge reading low or fluctuating
Often no symptoms besides the warning light

Common causes, most likely first

Faulty upper alternator voltage regulator
Open or shorted wiring in the upper alternator control circuit
Corroded or loose electrical connectors at the upper alternator
Failed powertrain control module (PCM) driver circuit
Poor ground connection for the upper alternator

How to diagnose and fix it

Inspect the upper alternator wiring harness and connectors for damage or corrosion
Check the upper alternator control circuit for continuity and shorts using a multimeter
Test the upper alternator output voltage and compare to specification
Verify the PCM control signal at the upper alternator connector
Repair or replace damaged wiring or connectors as needed
Replace the upper alternator if the regulator is faulty
Clear the code and retest the system to confirm the repair

Dual Alternator Circuit Checks Before Replacement

A common oversight is assuming the upper alternator itself is defective when the fault lies in the control circuit wiring or connectors.
The PCM may set P1105 due to a poor ground connection at the upper alternator, which is often overlooked during diagnosis.
In some cases, a weak battery or charging system issue can mimic a dual alternator fault, so always load test the battery first.
The upper alternator control circuit is separate from the lower alternator, so diagnosing only the lower unit will miss this fault.
Intermittent faults can be caused by chafed wiring that only shorts when the engine moves, requiring a wiggle test while monitoring live data.

Can I keep driving with P1105?

If the battery warning light is on, the vehicle may continue to run on the remaining alternator, but electrical loads should be minimized and the fault should be diagnosed promptly to avoid a no-start condition.

Tools that help

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Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.