P1D37 – AC Power Supply / AC Input Fuse 1

The Mitsubishi fault code P1D37 – AC Power Supply / AC Input Fuse 1 is a manufacturer-specific diagnostic trouble code stored by the On-Board Charger (OBC) or PHEV Control Unit (PCU) on Mitsubishi plug-in hybrid vehicles. It indicates that the OBC has detected a fault in the AC power supply circuit feeding the on-board charger — specifically associated with the first AC input fuse in the charging circuit. This code is most commonly encountered when the vehicle fails to charge via a Type 1 or Type 2 AC wallbox or domestic socket, and is a key code for any technician or owner troubleshooting Mitsubishi PHEV charging failures. Because P1D37 falls in the manufacturer-controlled P1xxx range, its definition and diagnostic approach are specific to Mitsubishi PHEV platforms.

What Does P1D37 Mean on a Mitsubishi PHEV?

The on-board charger in the Mitsubishi Outlander PHEV and Eclipse Cross PHEV converts incoming AC mains power into DC current to charge the high-voltage traction battery. Before the OBC begins this conversion process, it performs a series of pre-charge checks — verifying that the incoming AC supply is within specification, that the correct voltage and frequency are present, and critically, that the AC input protection fuses are intact and the supply circuit is continuous.

P1D37 is set when the OBC detects that AC Input Fuse 1 — one of the internal or external fuses protecting the AC supply to the charger — has blown, is showing an open circuit, or that the AC supply itself is absent or out of specification at that input. The OBC immediately halts the charging process and stores P1D37, illuminating the charge warning indicator. The vehicle’s drive capability is unaffected — P1D37 relates exclusively to the AC charging system — but the HV battery cannot be replenished via cable until the fault is resolved.

Symptoms of P1D37

P1D37 manifests primarily as a charging system fault rather than a drivability issue. Common symptoms include:

• Vehicle will not charge when connected to an AC wallbox, domestic socket, or public AC charging point
• Charging cable connected but no charging current flowing — charge indicator light on the vehicle does not turn green
• Orange or amber charging warning light illuminated on the instrument cluster or charge port area
• “Charging system fault” or equivalent message displayed on the MID or infotainment screen
• MUT-III or compatible scanner shows P1D37 stored in the OBC or PCU module
• Vehicle drives normally — no loss of power, no drivetrain warning lights in most cases
• HV battery state of charge slowly depletes over subsequent drives with no ability to replenish via cable
• In some cases, a blown fuse in the home consumer unit (circuit breaker tripped) is noted at the same time

Common Causes of P1D37

P1D37 can be triggered by faults both inside the vehicle and in the external charging infrastructure. The most common root causes are:

• Blown AC input fuse 1 inside the OBC — an internal fuse within the on-board charger has opened due to an overcurrent event, surge, or component failure within the OBC itself
• Blown external AC charging fuse — a fuse in the vehicle’s high-voltage junction box or fusebox protecting the AC input circuit has blown
• Faulty or incompatible charging cable (EVSE) — a damaged or non-compliant charging cable sending incorrect pilot signal or supply voltage to the OBC
• Faulty wallbox or charging point — the external AC supply is absent, out of voltage/frequency specification, or the EVSE is malfunctioning and not providing a valid charge authorisation signal
• Charge port inlet damage or contamination — moisture, debris, or physical damage to the charge port socket causing poor contact or a short circuit on the AC pins
• OBC internal fault — an internal failure within the on-board charger unit itself, often preceded by a surge or lightning event on the supply circuit
• Wiring fault between charge port and OBC — damaged, corroded, or chafed wiring in the AC supply harness between the charge inlet and the OBC
• Supply voltage out of specification — mains supply voltage significantly above or below normal (particularly relevant in some markets or with generator power supplies)

Affected Mitsubishi Vehicles

Tools & Equipment Required

Step-by-Step Diagnosis

Always begin with the simplest external checks before opening any vehicle panels or touching HV components:

• 1
  Confirm the Fault with a Full ScanConnect MUT-III or equivalent and scan all modules — OBC, PCU, ECM, EV-ECU. Record all DTCs. P1D37 should be present in the OBC or PCU. Note any companion codes — additional OBC codes alongside P1D37 may indicate an internal OBC failure rather than a simple fuse or supply issue.
• 2
  Test the Charging Cable & Wallbox FirstBefore suspecting the vehicle, verify the external infrastructure. Try a different charging cable (Mode 2 domestic cable or a different Mode 3 Type 1/Type 2 cable). Try a different charging point or wallbox if available. If the vehicle charges normally with a different cable or at a different location, the fault is in the original cable or wallbox — not in the vehicle.
• 3
  Inspect the Charge Port InletVisually inspect the vehicle’s charge port socket with a torch. Look for moisture or water ingress, debris or contamination between pins, bent, corroded, or burnt pins, and any signs of arcing or heat discolouration around the AC pins. Even slight moisture on the AC pins can trip the OBC’s protection circuitry and set P1D37. Dry the port thoroughly with compressed air if moisture is present.
• 4
  Check External AC Charging FusesLocate the HV junction box or charging fuse block — on the 1st Gen Outlander PHEV this is typically in the engine bay near the OBC unit. With the service plug removed and HV system isolated, inspect the AC input fuses using a DMM set to continuity or resistance. A blown fuse will show infinite resistance (open circuit). Note the fuse rating and replace only with an identical specification fuse.
• 5
  Inspect AC Wiring Harness from Charge Port to OBCTrace the AC supply wiring from the charge port inlet through the vehicle to the OBC. Check for chafing against body edges or sharp brackets, connector corrosion at the charge port connector and OBC input connector, and any signs of heat damage or melting. Resistance between supply and return conductors should be effectively zero (less than 1Ω) with no leakage to ground.
• 6
  Assess OBC Internal Fuse & Unit ConditionIf all external checks pass, the blown fuse may be internal to the OBC unit itself. Internal OBC fuse replacement requires OBC removal and disassembly — this is typically dealer or specialist territory. If the OBC has multiple companion codes or shows signs of internal failure (burn marks on casing, unusual odour), the entire OBC unit requires replacement rather than fuse-level repair.

Scanner Readout Explained

Below is a representative MUT-III diagnostic readout for a first-generation Outlander PHEV presenting with P1D37 following an attempted charge session on a domestic 13A socket with a Mode 2 cable.

====================================================
  MITSUBISHI MUT-III SE — DIAGNOSTIC REPORT
====================================================
  Vehicle:     2019 Outlander PHEV (GG3W)
  VIN:         JMBXNGA3WKZ0XXXXX
  Date:        2025-03-18  19:22:07
  Technician:  Workshop Bay 3
====================================================

MODULE: OBC (On-Board Charger)
----------------------------------------------------
  P1D37  AC Power Supply / AC Input Fuse 1
         Status:       Confirmed / Current
         Freeze Frame:
           HV Battery SOC:          28%
           Charge Session Status:   FAULT — No AC Current
           AC Input Voltage (L1):   0.0V
           AC Input Voltage (L2):   0.0V
           CP Signal (Pilot):       12.0V (cable connected, no charge auth)
           OBC Temperature:         21°C
           IG Status:               OFF

MODULE: PCU (PHEV Control Unit)
----------------------------------------------------
  No faults stored.

MODULE: ECM
----------------------------------------------------
  No faults stored.

MODULE: EV-ECU
----------------------------------------------------
  No faults stored.

====================================================
  LIVE DATA SNAPSHOT (IG ON, Cable Connected)
====================================================
  HV Battery Voltage:              298.1V
  HV Battery SOC:                  28%
  AC Input Voltage L1:             0.0V
  AC Input Voltage L2:             0.0V
  Control Pilot Signal:            12.0V
  OBC Status:                      FAULT
  OBC Temperature:                 21°C
  Charge Contactor Status:         OPEN
====================================================

This readout tells a clear diagnostic story. The Control Pilot (CP) signal is at 12.0V — meaning the charging cable is physically connected and the EVSE is communicating normally with the vehicle. However, AC input voltage on both L1 and L2 reads 0.0V at the OBC, confirming the OBC is not seeing any AC supply voltage despite the cable being connected. This points directly to an open circuit between the charge port and the OBC — either a blown fuse in the AC input circuit or a wiring break. The OBC itself is cool and has no companion internal fault codes, making an internal OBC failure less likely in this case.

Step-by-Step Repair Guide

Repair Path A: External AC Input Fuse Replacement

• 1
  Isolate the HV SystemRemove the service plug from the rear luggage area and wait a minimum of 10 minutes for HV capacitors to discharge before accessing any fuse block or junction box associated with the charging system. Don HV insulated gloves before proceeding.
• 2
  Locate & Replace the Blown FuseAccess the AC charging fuse block — consult the Mitsubishi workshop manual for your specific model year for the exact location, as it varies between GG3W and GN generations. Identify the blown AC input fuse 1, confirm it is open with a DMM, and replace with an identical specification fuse. Never substitute a higher-rated fuse — the fuse rating is calibrated to protect the OBC and wiring.
• 3
  Investigate Why the Fuse BlewA fuse does not blow without a reason. Before reinstating the service plug and attempting a charge, investigate the root cause — inspect the AC wiring for a short circuit, check the charge port pins for signs of arcing, and test the OBC input resistance. If the replacement fuse blows again immediately, a fault in the OBC or wiring is causing an overcurrent condition that must be resolved first.
• 4
  Clear Codes & Test Charge SessionReinstate the service plug, clear P1D37 using MUT-III, and attempt a charge session with a known-good charging cable. Monitor OBC live data to confirm AC input voltage is now present (230V on L1 for single-phase, or 230V on both L1 and L2 for three-phase) and that charge current is flowing. Confirm P1D37 does not return.

Repair Path B: Charge Port Inlet Replacement

• 1
  Remove the Charge Port AssemblyWith HV isolated, remove the charge port cover and surrounding trim panel. Disconnect the AC supply connector, the CP (Control Pilot) signal connector, and any locking actuator wiring. The charge port inlet on the 1st Gen Outlander PHEV is located on the front left of the vehicle behind a flap in the front bumper area.
• 2
  Fit OEM Replacement InletInstall a Mitsubishi OEM replacement charge port inlet — aftermarket inlets may not meet the correct contact resistance specification and can cause intermittent charging faults or future overcurrent events. Reconnect all connectors, ensure the locking actuator operates correctly, and refit the trim panel.
• 3
  Clear & VerifyClear all DTCs, reinstate the service plug, and perform a full charge session test. Verify with MUT-III live data that AC input voltage is present and stable throughout the charge session, charge current is flowing at the expected rate, and no DTCs return during or after charging.

Repair Path C: OBC Unit Replacement

• 1
  Confirm OBC Internal FailureOBC replacement is indicated when: all external fuses and wiring are intact, the charge port is undamaged, the external supply is verified healthy, but P1D37 persists or the replacement fuse blows immediately. Multiple OBC-internal DTCs alongside P1D37 further confirm internal OBC failure. This step must not be skipped — OBC units are expensive and should not be replaced on assumption alone.
• 2
  Remove & Replace the OBCWith HV fully isolated, remove the OBC unit — location varies by generation but is typically mounted in the engine bay. Disconnect all HV connectors (AC input, DC output to battery), LV signal connectors, and cooling connections if the OBC is liquid-cooled. Fit the replacement OBC unit, reconnect all connections, and torque all HV connectors to specification.
• 3
  Initialise & TestUse MUT-III to perform any required OBC initialisation or configuration procedure for the new unit. Clear all DTCs, reinstate the service plug, and perform a supervised charge session monitoring OBC live data throughout to confirm correct operation. Verify charge current, AC input voltage, DC output voltage, and OBC temperature all read within normal ranges.

Repair Cost Estimates

Prevention & Maintenance Tips

• Keep the charge port cover closed when not charging: The charge port inlet on the Outlander PHEV is not fully weatherproof when open. Moisture ingress during rain or car washing with the flap open is a leading cause of charge port pin corrosion and P1D37 false triggers.
• Inspect the charge port periodically: Every few months, inspect the charge port pins with a torch for any sign of corrosion, discolouration, or debris. Clean gently with a dry cloth or soft brush — never use metal tools or abrasives on the pins.
• Use quality charging cables: Cheap or non-certified charging cables may not maintain the correct Control Pilot signal, can have undersized conductors that overheat, and are more likely to cause overcurrent events that blow the AC input fuse. Use cables with IEC 62196 certification.
• Have your home wallbox inspected regularly: A wallbox with a failing contactor or relay can produce voltage spikes that damage the OBC’s input protection. Annual inspection by a qualified electrician is recommended, especially for older installations.
• Avoid charging during thunderstorms: Lightning-induced voltage surges on the domestic supply are a known cause of OBC internal fuse failure. Unplug the vehicle if a thunderstorm is forecast, or install a surge-protected EVSE.
• Do not use extension leads for charging: Charging via a standard domestic extension lead is not recommended — extension leads introduce additional resistance, can overheat under sustained charging current, and may cause the voltage at the vehicle end to fall below the OBC’s minimum input specification.

Frequently Asked Questions

Can I still drive my Mitsubishi PHEV with P1D37 stored?

Yes — P1D37 affects AC charging only and does not impact the vehicle’s ability to drive. The existing charge in the HV battery can still be used for EV driving, and the petrol engine will operate normally. However, since you cannot recharge via AC cable until the fault is resolved, the HV battery will gradually deplete over subsequent drives and the vehicle will eventually run exclusively on the petrol engine until repaired.

Why does P1D37 only appear when I use a specific charging cable or wallbox?

This strongly points to the charging cable or wallbox as the fault source rather than the vehicle. A specific cable or wallbox may have a marginal fault — slightly low output voltage, a worn contactor producing voltage spikes, or a Control Pilot signal out of tolerance — that the OBC’s protection circuitry detects and responds to with P1D37. Try the vehicle on multiple different cables and charge points to confirm. If P1D37 only appears with one specific cable or location, the fault is in that infrastructure, not in the car.

The AC input fuse keeps blowing — what does this mean?

A repeatedly blowing fuse always indicates an overcurrent condition in the circuit the fuse is protecting. Do not keep replacing the fuse without finding the root cause. The most likely causes are a short circuit in the AC wiring between the charge port and OBC, a damaged charge port inlet with shorted AC pins, or an internal OBC failure causing excessive current draw on the AC input. The OBC itself must be tested before assuming the wiring is at fault.

Is P1D37 covered under Mitsubishi’s warranty?

If the vehicle is within Mitsubishi’s standard warranty period, P1D37 and any associated OBC or charge port repair should be covered, provided the fault was not caused by misuse — such as using a non-certified charging cable, physical damage to the charge port, or an electrical surge from a non-compliant home installation. If the OBC has failed internally without any external cause, this is a warranty claim. Consult your Mitsubishi dealer with the full diagnostic report.

Can a generic OBD2 scanner read P1D37?

P1D37 is stored in the OBC module, which is a Mitsubishi-proprietary system not accessible via generic OBD2 readers. You will need a professional scanner with full Mitsubishi PHEV coverage — MUT-III, Autel MaxiSYS MS909, Launch X431 PAD VII, or similar. Some mid-range scanners with Mitsubishi coverage can read OBC codes; verify your specific tool’s compatibility before purchasing a scan service.

Does P1D37 affect DC rapid charging?

On Mitsubishi Outlander PHEVs equipped with CHAdeMO DC rapid charging, the DC charging circuit is largely separate from the AC on-board charger. P1D37 specifically relates to the AC input to the OBC, so DC rapid charging via the CHAdeMO port may still function normally even with P1D37 present — though this should be verified on your specific vehicle as architecture differs between generations. If DC charging is also failing, additional fault codes specific to the DC charging circuit will typically be present alongside P1D37.

How long does an OBC replacement take?

OBC replacement on a first-generation Outlander PHEV typically takes 3–5 hours at a dealer workshop. This includes HV system isolation, OBC removal and replacement, reconnection of all HV and LV connectors to correct torque specifications, any required software initialisation of the new unit, and a post-replacement charge session test. It is not a job for a general workshop without HV vehicle training — OBC work involves live high-voltage circuits that require specialist safety procedures.

Can moisture alone cause P1D37 without any permanent damage?

Yes — moisture ingress into the charge port is one of the most common causes of a transient P1D37. If the port is dried out thoroughly with compressed air and left to air dry completely, the code can often be cleared and charging resumes normally with no permanent damage. However, if moisture has been present for an extended period or if there are signs of corrosion on the pins, the charge port inlet should be replaced to prevent recurrence and to ensure charging contact resistance remains within specification.

Conclusion

Mitsubishi P1D37 – AC Power Supply / AC Input Fuse 1 is a charging system fault that prevents AC cable charging on Mitsubishi PHEV vehicles. While the code sounds complex, the diagnostic process follows a clear hierarchy — always start with the simplest and cheapest checks first. A different charging cable, a dry charge port, or a replaced fuse resolves the majority of P1D37 cases without touching the OBC itself.

OBC replacement — the most expensive outcome — is only necessary in a minority of cases where internal OBC failure is confirmed after all external causes have been eliminated. A thorough diagnostic scan with MUT-III and a methodical approach to the external charging circuit will identify the true fault quickly and save significant unnecessary expenditure.