P1D37 – AC power supply/AC input fuse 1 (Mitsubishi)

Mitsubishi-specific code — factory diagnostic data

Last updated: April 2, 2026

Definition source: Mitsubishi factory description · Autel MaxiSys Ultra & EV. Diagnostic guidance is based on factory-defined fault logic for this code.

P1D37 means your 2016 Mitsubishi Outlander has detected a problem with the AC power supply path, specifically “AC input fuse 1.” In plain terms, the vehicle may not accept external AC charging or may stop charging unexpectedly. According to Mitsubishi factory diagnostic data, this is a Mitsubishi-defined code that points to the AC power supply/AC input fuse 1 circuit as the suspected trouble area. This code does not prove a bad fuse by itself. The control module sets it when the expected AC input power or fuse circuit status does not match what it should see during charging-related checks.

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P1D37 Quick Answer

P1D37 on Mitsubishi indicates the vehicle sees an issue with the AC power supply feed related to “AC input fuse 1.” Diagnose the fuse circuit and its power/ground path under load before replacing any parts.

What Does P1D37 Mean?

Official definition: “AC power supply/AC input fuse 1.” The module detected an abnormal condition in the AC input power supply circuit that uses AC input fuse 1. In practice, this usually shows up as no AC charging, interrupted charging, or a charge system warning while plugged in.

What the module is checking and why it matters: The charging control logic monitors the AC input power path and related fuse sense logic. The exact layout varies by Mitsubishi platform, but the module expects a valid power supply state when AC charging is requested. If the module sees a mismatch, such as an “open” indication when power should exist, it sets P1D37. That matters because an open fuse, a high-resistance connection, or a wiring fault can mimic a failed charger component. Confirm the circuit condition with voltage-drop and continuity checks before you touch parts.

Theory of Operation

During normal AC charging, external AC power enters the vehicle through the charge inlet. The system routes that power through protection devices, including one or more AC input fuses. The onboard charging system then converts AC to DC to charge the high-voltage battery. Mitsubishi uses module logic to verify that the AC input path behaves correctly during enable, charging, and shut-down events.

P1D37 sets when the module does not see the expected electrical state for “AC input fuse 1.” An open fuse can cause it. Corrosion at the fuse terminals can also cause it. A loose connector, damaged harness, or incorrect fuse rating can create a voltage drop that looks like a supply loss. Some faults only appear under load, so a fuse can pass a quick visual check but fail an actual charging event.

Symptoms

You will usually notice this code during an attempted AC charge event.

• Charging failure The vehicle will not start AC charging when plugged in
• Interrupted charging Charging starts, then stops after a short time
• Charge warning A charge system warning message or indicator appears during plug-in
• No “ready” charge state The EVSE shows a fault or never transitions to active charging
• Intermittent behavior Charging works sometimes, then fails at the next plug-in
• Related DTCs Other charging or power supply codes may store with P1D37
• Clicking or relay activity You may hear repeated enable attempts from charge system relays

Common Causes

• Blown AC input fuse 1: A failed fuse opens the AC input power path, so the module sees no usable AC supply.
• High resistance at the AC input fuse terminals: Heat, looseness, or oxidation at the fuse blades creates voltage drop under load and triggers an AC supply plausibility fault.
• Corrosion or water intrusion in the AC input power distribution: Moisture in the fuse box or related junction points increases resistance and interrupts AC input continuity.
• Open circuit in the AC input feed wiring: A broken conductor between the AC inlet/power source path and the monitored fuse circuit prevents the module from detecting expected input power.
• Short to ground on the AC input circuit: A chafed harness or pinched wiring can pull current high and blow the fuse or collapse the sensed input.
• Short to power or cross-feed from another circuit: Backfeeding can distort the AC input sense signal and cause the module to flag fuse 1 input as invalid.
• Poor ground at the monitored module or power distribution point: A weak ground can skew internal sensing and create an apparent loss of AC input even when the fuse remains intact.
• Connector pin fit or terminal damage at the fuse box or related connector: Spread terminals and poor pin tension cause intermittent opens that often set the DTC during vibration or load changes.
• Internal fault in the monitored module’s AC input sensing circuit: A failed sensing stage can report a fuse/input fault even with correct power and wiring, but only after external checks pass.

Diagnosis Steps

Use a scan tool that can read Mitsubishi-specific P1 codes, plus data stream and pending codes. Have a quality DMM, a fused test light, and back-probing leads. A wiring diagram and fuse box layout matter for this code. Plan to do voltage-drop tests under load, not continuity checks alone, because high resistance often hides until current flows.

1. Confirm P1D37 on the scan tool and record stored, pending, and history codes. Save freeze frame data for battery voltage, ignition state, and any related charging or power supply parameters shown. Freeze frame captures the conditions when the DTC set. Use a manual scan tool snapshot later to catch an intermittent drop during a wiggle test or load test.
2. Inspect the AC input fuse 1 area first, before probing any module connectors. Check the correct fuse cavity and rating for the Mitsubishi Outlander platform you service. Look for heat discoloration, melted plastic, or a loose fuse fit. Verify the fuse element visually, then confirm with a meter because hairline opens can fool the eye.
3. Verify power distribution to the fuse under the same key state that set the code. Use a test light or meter to confirm power exists on the feed side of the fuse. Then check the load side of the fuse. If power appears on the feed side but not the load side, you have a fuse or fuse contact issue, not a module problem.
4. Load-test the fuse contacts to find high resistance. Keep the circuit powered as the vehicle would during the fault condition. Measure voltage drop across the fuse blades while the circuit operates. A good fuse and tight terminals show very low drop. Large drop points to loose terminals, corrosion, or heat damage in the fuse box.
5. Check the module power and ground integrity under load, not by continuity alone. Back-probe the module power feed related to this monitored AC input path, if service information identifies it. Perform a voltage-drop test on grounds with the circuit operating. Keep ground drop under 0.1V with the circuit loaded, because higher drop can corrupt sensing.
6. Inspect connectors and harness routing from the AC input path through the fuse box to the monitored circuit. Focus on areas near the fuse box, pass-throughs, and any points where the harness can rub. Look for green corrosion, pushed-out pins, spread terminals, and aftermarket splices. Repair terminal fit issues before replacing components.
7. Check for shorts that could blow or stress AC input fuse 1. With power off and the fuse removed, test the load side for a short to ground using resistance and then a fused test light method. Do not rely on ohms alone if the fault acts intermittent. If the fused test light glows bright, locate the short by isolating branches per the wiring diagram.
8. Perform a controlled wiggle test while watching live data and capture a scan tool snapshot. Move the harness at the fuse box, connector bodies, and known rub points. Freeze frame shows what happened when it set. The snapshot proves what changes during your test, which helps you pinpoint an intermittent open or high resistance point.
9. Differentiate pending versus confirmed behavior during verification. If the code shows as pending only, the fault may have occurred once and not repeated yet. Many OBD-II Type B strategies need two similar trips to confirm. If this Mitsubishi monitor runs continuously, a hard fault often returns immediately on key-on after clearing.
10. After repairs, reinstall the correct fuse and restore all connectors. Clear codes and run the vehicle through the same operating conditions seen in freeze frame. Confirm the AC input/fuse-related data remains stable. Recheck for returning pending codes before releasing the vehicle.
11. If all external power, ground, fuse fitment, and wiring checks pass, then evaluate the monitored module’s input sensing circuit. Confirm you supply correct inputs at the module pin during the fault condition. Only then consider module-level repair or replacement. Reprogramming and immobilizer registration requirements vary by Mitsubishi platform, so verify service procedures first.

Professional tip: Do not stop after a fuse element “looks good.” P1D37 often comes from heat at the fuse terminals, not the fuse link. Always measure voltage drop across the fuse and across the fuse box connection under load. That test finds loose tension and corrosion that a continuity check will miss.

Possible Fixes

• Replace AC input fuse 1 only after confirming why it failed: Install the correct rating and recheck for overcurrent, shorts, or melted terminals.
• Restore fuse box terminal tension and repair heat damage: Clean corrosion, repair or replace damaged terminals, and correct any looseness that caused voltage drop.
• Repair open or shorted wiring in the AC input path: Fix chafed insulation, broken conductors, and poor splices, then secure routing to prevent repeat failure.
• Service contaminated connectors: Remove corrosion, replace damaged pins, and correct pin fit issues at the fuse box or in-line connectors.
• Correct module power or ground faults: Repair ground points and power feeds, then verify with voltage-drop testing under load.
• Update or replace the monitored module only after circuit verification: Confirm the module receives correct inputs and grounds before any module decision.

Can I Still Drive With P1D37?

You can usually drive a 2016 Mitsubishi Outlander with P1D37, but you should treat it as an “EV charging system not available” warning. This DTC points to the AC power supply or “AC input fuse 1” circuit that supports AC charging hardware. When the module sees that circuit missing or implausible, it may disable AC charging and log the code. Driving on the gasoline engine may feel normal, but you can lose plug-in charging and some hybrid functions depending on the platform. Do not ignore any burning smell, melted plastic, or repeat fuse failure. Park the vehicle and diagnose it before further driving in those cases.

How Serious Is This Code?

P1D37 ranges from an inconvenience to a high-priority electrical fault. If the only symptom involves AC charging failure, the vehicle often remains drivable but loses the ability to replenish the high-voltage battery from the wall. The seriousness increases fast when the fuse opens repeatedly or the fuse area shows heat damage. That pattern points to excessive current draw, a short, or high resistance at a connection. Those conditions can damage connectors and housings. They can also create a fire risk near the charge inlet and power supply components. Treat any evidence of overheating, moisture intrusion, or arcing as urgent and stop driving until you confirm the cause.

Common Misdiagnoses

Technicians often replace the charger-related unit or a control module because the scan tool text mentions “AC power supply.” That skips the basic electrical checks that actually prove the fault. Another common mistake involves checking the fuse with an ohmmeter only. A fuse can pass a continuity test yet fail under load because of heat damage at the blades. Many also miss the real failure point: spread terminals, corrosion, or a partially seated connector at the fuse block or AC input harness. Avoid wasted spending by verifying power feed, load-side voltage under load, and connector pin tension before any module decisions.

Most Likely Fix

The most frequent confirmed repair direction starts at “AC input fuse 1” integrity and its connections. Verify the fuse holds and carries current without voltage drop or heat. Then correct the reason it opened or read low. That often means repairing a shorted or rubbed-through section of the AC input supply wiring, cleaning and tightening a corroded fuse block terminal, or reseating a loose connector near the charging power supply path. If the circuit checks good and the code returns, follow Mitsubishi service information to test the AC input sensing circuit at the module before condemning any charger or control unit.

Repair Costs

Repair cost depends on whether the confirmed root cause is wiring, connector condition, a sensor, a module, or the labor needed to diagnose the fault correctly.