Faulty alternator, particularly a failed FR terminal or internal regulator; Damaged or corroded wiring between the alternator FR terminal and the ECM; Loose or dirty electrical connectors at the alternator or ECM; Blown fuse or fusible link in the charging circuit; Poor ground connection for the alternator or engine block; ECM internal fault (rare)

DTC codes / Mitsubishi codes / P1500

P1500 · MitsubishiAlternator FR Terminal Circuit

Q: What does code P1500 mean?

Alternator FR Terminal Circuit. P1500 on Mitsubishi vehicles indicates that the engine control module (ECM) has detected an abnormal signal from the alternator's FR (field return) terminal circuit, which is used to monitor the alternator's load on the engine. The ECM expects a specific voltage pattern on this circuit and sets the code when the signal is out of range, indicating a fault in the wiring, connector, or alternator itself.

P1500 on Mitsubishi vehicles indicates that the engine control module (ECM) has detected an abnormal signal from the alternator's FR (field return) terminal circuit, which is used to monitor the alternator's load on the engine. The ECM expects a specific voltage pattern on this circuit and sets the code when the signal is out of range, indicating a fault in the wiring, connector, or alternator itself.

SystemPowertrain

Code typeMitsubishi specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Battery warning light illuminated on the dashboard
Dimming or flickering headlights and interior lights
Battery frequently going dead or needing a jump start
Erratic engine idle or stalling, especially when electrical loads are applied
Often no symptoms besides the warning light

Common causes, most likely first

Faulty alternator, particularly a failed FR terminal or internal regulator
Damaged or corroded wiring between the alternator FR terminal and the ECM
Loose or dirty electrical connectors at the alternator or ECM
Blown fuse or fusible link in the charging circuit
Poor ground connection for the alternator or engine block
ECM internal fault (rare)

How to diagnose and fix it

Inspect the battery and charging system basics: check battery voltage and alternator belt condition
Visually inspect the alternator FR terminal wiring and connector for damage or corrosion
Measure voltage on the FR circuit at the alternator and at the ECM to check for continuity and correct signal
Check for blown fuses or fusible links related to the charging system
Perform a voltage drop test on the ground circuits for the alternator and ECM
If wiring and connections are good, test the alternator output and FR signal with an oscilloscope or scan tool
Replace the alternator if the FR terminal or internal regulator is confirmed faulty

Before you replace the alternator

A loose or corroded FR terminal connector is a common cause that mimics a failed alternator, so always inspect the connector before condemning the alternator.
The FR signal is a duty-cycle signal that the ECM uses to adjust idle speed; a fault can cause idle problems even if the battery still charges.
Some aftermarket alternators do not provide the correct FR signal, leading to repeated P1500 codes even though the charging system works.
The code can be set by a poor ground connection at the engine block, which affects the FR circuit reference voltage.
Always check for related codes like P0500 or P0560, as they can indicate a shared power or ground issue.

Can I keep driving with P1500?

You can drive the vehicle short distances, but avoid relying on it for long trips because the alternator may not be charging correctly, leading to a dead battery and stalling. Have the charging system inspected promptly to prevent being stranded.

Tools that help

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