P1D23 – Power Circuit (Pre-charge Fail)

The Mitsubishi fault code P1D23 – Power Circuit (Pre-charge Fail) is a manufacturer-specific diagnostic trouble code stored by the PHEV Control Unit (PCU) on Mitsubishi plug-in hybrid vehicles. It indicates that the high-voltage system has failed to complete its pre-charge sequence — a critical safety and protection process that must occur every time the vehicle is switched on before the main HV contactors close and high voltage is distributed to the inverter, motors, and drive system. P1D23 is one of the more serious PHEV-specific fault codes because a pre-charge failure means the vehicle cannot enable its HV drive system at all, leaving the car either fully immobile or restricted to a very limited emergency mode. Understanding the pre-charge circuit and the specific failure modes that trigger P1D23 is essential for any technician or knowledgeable owner dealing with a Mitsubishi PHEV that refuses to ready-up or drive.

What Does P1D23 Mean on a Mitsubishi PHEV?

Every time a Mitsubishi PHEV is switched on, the PCU executes a pre-charge sequence before closing the main positive and negative HV contactors. The purpose of pre-charge is to slowly charge the large smoothing capacitors inside the inverter up to near battery voltage — typically 280–330V on first-generation Outlander PHEVs — through a current-limiting pre-charge resistor and a dedicated pre-charge contactor. This controlled ramp-up prevents the catastrophic inrush current spike that would occur if the main contactors were closed directly onto discharged capacitors, which would weld the contacts, destroy the inverter, or cause an arc flash event.

The PCU monitors inverter bus voltage throughout the pre-charge process and expects it to reach a defined percentage of battery voltage within a set time window — typically around 90% of HV battery voltage within 3–5 seconds. P1D23 is stored when this threshold is not reached in time, or when the bus voltage fails to rise at all during the pre-charge window. The PCU immediately aborts the startup sequence, keeps all main contactors open, and stores P1D23 to protect the inverter and contactor assembly from damage.

Symptoms of P1D23

Because P1D23 prevents the HV system from enabling, its symptoms are immediately noticeable and severe:

• Vehicle will not enter READY mode — the READY indicator on the instrument cluster does not illuminate after pressing the start button
• Red hybrid system warning light illuminated on the instrument cluster
• “Stop Vehicle — Check Hybrid System” or equivalent critical warning message on the MID
• Vehicle completely immobile — no EV drive, no petrol engine start via MG1, no movement possible
• In some cases the 12V systems (lights, infotainment, instruments) function normally but the PHEV drivetrain is entirely unresponsive
• Repeated start attempts produce the same result — the PCU detects pre-charge failure on every cycle and refuses to close main contactors
• MUT-III or compatible scanner stores P1D23 in the PCU module, often accompanied by additional HV system codes

Common Causes of P1D23

Pre-charge failures have a relatively focused set of root causes — the pre-charge circuit itself is not complex, but each component in it is critical:

• Failed pre-charge contactor — the dedicated pre-charge relay/contactor has failed open and is not closing during the pre-charge sequence, preventing any current from flowing through the pre-charge resistor to the inverter capacitors
• Failed pre-charge resistor — the current-limiting resistor in series with the pre-charge contactor has burned out (open circuit), preventing capacitor charging even when the contactor closes correctly
• Failed main positive or negative contactor — a welded or stuck-open main contactor interferes with the pre-charge voltage measurement, causing the PCU to see an incorrect bus voltage reading
• Inverter capacitor failure — shorted or severely degraded smoothing capacitors inside the inverter present an abnormally low impedance load, causing excessive inrush that trips protection and prevents pre-charge completion
• HV battery pack fault — a significantly degraded or internally faulted HV battery with very high internal resistance cannot supply sufficient current through the pre-charge circuit to charge the inverter capacitors within the time window
• HV wiring open circuit or high resistance connection — a break or corroded connection in the orange HV cables between the battery junction box and inverter introduces resistance that slows or prevents capacitor charging
• PCU internal fault — in rare cases the PCU’s own contactor driver circuit or bus voltage measurement circuit fails, causing incorrect pre-charge sequencing or a false P1D23 reading
• Low HV battery state of charge — an extremely depleted HV battery (near 0% SOC) may not have sufficient voltage to drive the pre-charge circuit to the required threshold, particularly in cold conditions

Common Misdiagnoses

P1D23 is a high-impact code that can lead technicians toward expensive component replacements before the true fault is identified. These are the most frequently encountered misdiagnoses:

• HV battery pack condemned unnecessarily: The HV battery is frequently blamed for P1D23, particularly on high-mileage vehicles. In practice, the pre-charge contactor or resistor — both far cheaper components — is the root cause in the majority of cases. Always test the contactor assembly before considering battery replacement.
• PCU replacement before contactor testing: Because P1D23 is stored in the PCU, some technicians assume the PCU itself has failed. PCU failure as the primary cause of P1D23 is rare. The PCU is correctly detecting a pre-charge failure — it is reporting the fault, not causing it. Test all contactor and circuit components first.
• Inverter replacement before capacitor testing: A sluggish pre-charge that eventually completes but takes too long can be mistaken for an inverter failure. Inverter capacitor degradation causes slow pre-charge; a short circuit within the inverter prevents it entirely. These are different faults requiring different responses — confirm with live data before condemning the inverter.
• 12V battery overlooked: A weak 12V auxiliary battery cannot reliably power the PCU’s contactor driver circuits at the required voltage during the startup sequence. P1D23 caused by a failing 12V battery is frequently misdiagnosed as a contactor or HV battery fault — always test the 12V system first as it costs nothing and takes minutes.

Affected Mitsubishi Vehicles

Tools & Equipment Required

Step-by-Step Diagnosis

Work through this sequence methodically — always start with the cheapest and safest checks before approaching HV components:

• 1
  Full Multi-Module ScanConnect MUT-III or equivalent and scan all modules — PCU, ECM, EV-ECU, ETACS, BMS. Record every DTC present and all freeze frame data. Pay close attention to any BMS (Battery Management System) codes stored alongside P1D23 — these may indicate whether the HV battery itself is contributing to the failure or whether the fault is isolated to the contactor circuit.
• 2
  Test the 12V Auxiliary Battery FirstBefore touching anything HV-related, load-test the 12V auxiliary battery. The PCU’s contactor driver circuits require stable 12V supply to operate correctly. A battery dropping below 10V under load will cause unreliable contactor operation and can trigger P1D23 even when the HV system is healthy. Charge or replace a weak 12V battery before proceeding — this takes 20 minutes and costs nothing if the battery passes.
• 3
  Check HV Battery SOCIn MUT-III live data, verify the HV battery state of charge. A SOC below 5–10% may provide insufficient voltage to drive the pre-charge circuit to the required threshold — particularly in cold ambient temperatures where battery internal resistance increases significantly. If SOC is critically low, attempt a charge session first. If the vehicle cannot charge due to additional faults, this step will need to be revisited after other repairs.
• 4
  Perform Contactor Actuator Test via MUT-IIIUsing MUT-III active tests, command the pre-charge contactor to close and monitor the inverter bus voltage in live data. A healthy pre-charge sequence will show bus voltage rising from near 0V to within 90% of HV battery voltage within approximately 3–5 seconds. No voltage rise indicates the pre-charge contactor or resistor is open circuit. A slow rise that does not reach threshold points to a degraded pre-charge resistor or inverter capacitor issue.
• 5
  Isolate HV System & Test Contactor AssemblyRemove the service plug and wait 10 minutes. Access the main junction box / contactor assembly. With HV isolated, use a DMM to measure continuity across the pre-charge contactor terminals (should be open with no command) and across the pre-charge resistor (should show a specific resistance value — typically 10–40Ω depending on variant, consult workshop manual). An open-circuit resistor reading (infinite resistance) confirms the pre-charge resistor has failed.
• 6
  Inspect HV Wiring for Open Circuit or High ResistanceWith service plug removed, use a DMM to check continuity along the orange HV cables between the battery junction box and inverter input terminals. Any resistance above 0.5Ω in these cables indicates a connection fault. Inspect all orange cable connectors for corrosion, heat damage, or looseness. Use a megohmmeter to verify cable insulation integrity — resistance between conductor and vehicle chassis should exceed 1MΩ.

Scanner Readout Explained

Below is a representative MUT-III diagnostic readout for a first-generation Outlander PHEV presenting with P1D23 due to a failed pre-charge resistor in the main junction box.

====================================================
  MITSUBISHI MUT-III SE — DIAGNOSTIC REPORT
====================================================
  Vehicle:     2016 Outlander PHEV (GG3W)
  VIN:         JMBXNGA3WGZ0XXXXX
  Date:        2025-03-22  10:14:33
  Technician:  Workshop Bay 2
====================================================

MODULE: PCU (PHEV Control Unit)
----------------------------------------------------
  P1D23  Power Circuit (Pre-charge Fail)
         Status:       Confirmed / Current
         Freeze Frame:
           HV Battery SOC:              54%
           HV Battery Voltage:          301.6V
           Inverter Bus Voltage:        0.0V
           Pre-charge Status:           FAIL — Timeout
           12V Supply Voltage:          12.8V
           Ambient Temperature:         11°C
           IG Status:                   ON

MODULE: BMS (Battery Management System)
----------------------------------------------------
  No faults stored.

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

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

====================================================
  LIVE DATA SNAPSHOT (IG ON — Pre-charge Attempt)
====================================================
  HV Battery Voltage:              301.6V
  HV Battery SOC:                  54%
  Inverter Bus Voltage:            0.0V
  Pre-charge Contactor Status:     CLOSED (commanded)
  Main Contactor (+):              OPEN
  Main Contactor (-):              OPEN
  12V Auxiliary Battery:           12.8V
  PCU Temperature:                 14°C
  Inverter Temperature:            12°C
====================================================

This readout provides a precise diagnostic picture. The HV battery is healthy at 301.6V with 54% SOC and the 12V system is strong at 12.8V — ruling out both as root causes immediately. The PCU is correctly commanding the pre-charge contactor closed, but the inverter bus voltage remains at 0.0V throughout the pre-charge window. This confirms current is not flowing through the pre-charge circuit despite the contactor being commanded closed — pointing directly to an open-circuit pre-charge resistor or a failed pre-charge contactor that is not actually closing despite the PCU command. Physical testing of the resistor and contactor with a DMM confirmed an open-circuit pre-charge resistor in this case.

Step-by-Step Repair Guide

Repair Path A: Pre-charge Resistor / Contactor Assembly Replacement

• 1
  Isolate HV SystemRemove the service plug from the rear luggage compartment and wait a minimum of 10 minutes. Confirm HV isolation with a CAT III rated DMM — measure between HV positive and negative terminals at the junction box to verify voltage has discharged below 60V DC before proceeding. Don Class 0 HV insulated gloves throughout.
• 2
  Access the Main Junction BoxOn first-generation Outlander PHEVs the main junction box containing the contactor assembly is located in the engine bay. Remove the cover carefully — note the orientation of all connectors before disconnecting. The pre-charge resistor and contactor are typically integrated into the junction box assembly as a serviceable sub-assembly on GG3W variants.
• 3
  Replace the Faulty ComponentReplace the confirmed failed component — pre-charge resistor, pre-charge contactor, or complete junction box assembly depending on parts availability and the extent of damage. Use Mitsubishi OEM parts only for contactor assemblies — aftermarket contactors may not meet the required switching speed, contact resistance, or current rating for the PHEV application. Torque all HV terminal bolts to the specification in the workshop manual.
• 4
  Reinstate Service Plug & Verify Pre-chargeReinstate the service plug and connect MUT-III. Attempt a startup and monitor inverter bus voltage in live data during the pre-charge sequence. Bus voltage should rise smoothly from 0V to within 90% of HV battery voltage within 3–5 seconds. Main contactors should then close and the vehicle should enter READY mode. Clear all DTCs and confirm P1D23 does not return.

Repair Path B: HV Wiring Repair

• 1
  Locate the Fault PointWith HV isolated, use a DMM to perform a voltage drop / continuity test along each HV cable section between the junction box and inverter. Isolate the specific section showing high resistance or open circuit. Inspect the full length of that cable section for physical damage, crush points, or connector corrosion.
• 2
  Replace — Never Repair — HV CablesHV orange cables must be replaced as complete sections — never spliced, soldered, or taped. The insulation specification and conductor cross-section of HV cables are safety-critical. Fit OEM replacement cable sections, route correctly away from heat sources and sharp edges, and torque all terminal connections to workshop manual specification.
• 3
  Insulation Test & VerifyBefore reinstating the service plug, perform a megohmmeter insulation resistance test between the repaired cable conductor and vehicle chassis. Resistance must exceed 1MΩ — ideally significantly higher. Reinstate service plug, clear all DTCs, and verify pre-charge completes successfully with MUT-III live data.

Repair Cost Estimates

Prevention & Maintenance Tips

• Maintain the 12V auxiliary battery proactively: The 12V battery powers the contactor driver circuits. Annual load testing and replacement at 4–5 years prevents 12V-induced HV system faults including P1D23 from occurring in the first place.
• Avoid allowing the HV battery to fully deplete: Running the HV battery to near 0% SOC regularly accelerates cell degradation and increases internal resistance — both of which can eventually cause pre-charge timeouts. Keep SOC above 10–15% where possible.
• Do not attempt to jump-start a PHEV from another vehicle: Incorrect jump-starting procedures can send voltage spikes through the 12V system that damage contactor driver circuits and PCU components, potentially causing P1D23 and other HV system faults. Use a proper 12V battery charger or jump starter rated for modern vehicles.
• Inspect orange HV cables during any underbody work: Any time the vehicle is on a ramp for brake, exhaust, or suspension work, ask the technician to visually check orange HV cable routing for abrasion or damage. Early identification of cable wear prevents an open-circuit fault developing.
• Address other HV fault codes promptly: Ignoring early-stage HV system codes — particularly BMS cell balance warnings or contactor wear indicators — allows the underlying condition to deteriorate until it triggers P1D23 and a no-start situation. Regular MUT-III health checks on PHEV vehicles are a worthwhile investment.

Frequently Asked Questions

My Mitsubishi PHEV won’t start and shows P1D23 — is it safe to attempt multiple restarts?

Repeated restart attempts will not resolve P1D23 and are not recommended. Each failed pre-charge attempt places stress on the contactor assembly — particularly if the fault is a partially functioning contactor that is closing intermittently. More importantly, if the pre-charge failure is caused by an inverter capacitor fault, repeated attempts could worsen the internal damage. Switch off, have the vehicle recovered to a workshop, and diagnose before attempting further starts.

Can P1D23 appear intermittently and then clear itself?

Yes — intermittent P1D23 is actually a concerning presentation because it often indicates a contactor or connection that is failing progressively rather than having failed completely. An intermittent fault that clears and allows the vehicle to start will eventually become a permanent fault. Intermittent P1D23 should be diagnosed and repaired as urgently as a permanent one — do not wait for the fault to become consistent before acting.

Does P1D23 mean my HV battery needs replacing?

Not necessarily — and in most cases, no. The HV battery is only responsible for P1D23 if it has such severe internal resistance degradation or such critically low SOC that it cannot supply sufficient current through the pre-charge circuit. In practice the pre-charge resistor, pre-charge contactor, or 12V auxiliary battery are the root cause in the majority of P1D23 cases. A thorough diagnostic process as described in this guide will identify whether the HV battery is genuinely implicated before any replacement decision is made.

Can I diagnose P1D23 without MUT-III?

Partially. A professional aftermarket scanner with Mitsubishi PHEV coverage such as the Autel MaxiSYS MS909 can read P1D23 and access some PCU live data. However, the contactor actuator test — which is the most important diagnostic step for isolating the pre-charge circuit fault — may only be available on MUT-III. For a definitive diagnosis of P1D23, MUT-III or dealer-level access is strongly recommended.

Why does cold weather seem to trigger P1D23 more often?

Cold temperatures increase the internal resistance of both the HV traction battery and the 12V auxiliary battery. A marginally degraded HV battery that passes pre-charge at 20°C may fail the pre-charge time window at -5°C because its higher cold-temperature resistance slows the capacitor charging rate. Similarly, a 12V battery that barely powers the contactor driver circuits at room temperature will fall below the required threshold in cold conditions. P1D23 appearing only in cold weather is a strong indicator that one or both batteries are near end of life.

What is the pre-charge resistor and why does it fail?

The pre-charge resistor is a high-power resistor — typically rated at several hundred watts — connected in series with the pre-charge contactor. It limits the initial inrush current to the inverter capacitors to a safe level. Because it carries significant current during every startup sequence, it experiences thermal cycling stress with every ignition cycle over the vehicle’s life. On high-mileage vehicles that have performed tens of thousands of startup cycles, the resistor element can eventually fail open-circuit — a normal wear-related failure rather than an indication of any other system fault.

Is P1D23 covered under Mitsubishi’s PHEV warranty?

If the vehicle is within Mitsubishi’s standard warranty period, P1D23 and the associated repair should be covered. The pre-charge resistor and contactor assembly are considered PHEV drivetrain components. In markets where Mitsubishi offers an extended PHEV drivetrain warranty (separate from the standard vehicle warranty), these components may be covered beyond the standard term. Check your specific warranty documentation and present the full MUT-III diagnostic report to your dealer.

Conclusion

Mitsubishi P1D23 – Power Circuit (Pre-charge Fail) is a serious fault that prevents the HV drive system from enabling, leaving the vehicle immobile. However, the root cause is almost always a specific, identifiable component failure in the pre-charge circuit rather than a catastrophic HV system failure. A failed pre-charge resistor or contactor — both relatively affordable and accessible components — accounts for the majority of P1D23 cases encountered in practice.

The diagnostic process is straightforward when approached methodically: start with the 12V battery, use MUT-III to perform a live pre-charge test and observe inverter bus voltage behaviour, then physically test the contactor and resistor with a DMM. This sequence identifies the fault component quickly and prevents unnecessary replacement of expensive HV batteries or inverters. As with all high-voltage PHEV work, proper isolation procedures and qualified HV technician involvement are non-negotiable.