P1B28 – Crash Detection (Mitsubishi)

The Mitsubishi fault code P1B28 – Crash Detection is a manufacturer-specific diagnostic trouble code stored by the PHEV Control Unit (PCU) on Mitsubishi plug-in hybrid vehicles. It indicates that the PCU has received a crash detection signal — either from a genuine collision event or from a false trigger — and has responded by commanding an emergency shutdown of the high-voltage system. This is one of the most safety-critical DTCs in the Mitsubishi PHEV system, as its primary purpose is to protect occupants and first responders from high-voltage electrocution following an accident. Understanding P1B28 is essential for any technician or owner dealing with a post-collision PHEV or an unexplained HV system shutdown.

What Does P1B28 Mean on a Mitsubishi PHEV?

P1B28 is a Mitsubishi-proprietary PCU code that is set when the PCU receives a crash signal via the CAN bus from the SRS (Supplemental Restraint System) / Airbag Control Unit. In a collision severe enough to deploy airbags — or in some cases to trigger the crash sensor threshold without deployment — the SRS ECU broadcasts a crash event message across the CAN network. The PCU monitors this broadcast and, upon receipt, immediately opens the HV system main contactors (relays), disconnecting the high-voltage battery from the drive system and charger circuits.

This emergency isolation is a deliberate and correct safety response. However, once the PCU has stored P1B28, the HV system will not re-enable automatically — even after the vehicle is repaired and restarted. The code must be cleared by an authorised diagnostic tool after a qualified inspection confirms the vehicle is structurally and electrically safe to return to service.

Symptoms of P1B28 – Crash Detection

When the PCU stores P1B28 and isolates the HV system, the following symptoms are typically observed:

• Vehicle will not drive — HV system is fully isolated, no traction power available from either electric motor
• Red hybrid system warning light on the instrument cluster
• “Stop Vehicle — Check Hybrid System” or equivalent message on the MID
• Petrol engine may or may not start — depending on whether 12V system is intact — but the vehicle cannot move under PHEV power
• HV battery charging via cable is disabled
• Regenerative braking inoperative
• All airbag warning lights illuminated (in post-collision scenarios)
• In false-trigger scenarios: vehicle suddenly loses all drive power without any visible collision damage

Common Causes of P1B28

P1B28 has two distinct root cause categories — genuine crash events and false triggers — both of which require different approaches:

Genuine Collision Events

• Front, rear, or side impact sufficient to trigger SRS sensors — the most common and intended trigger for P1B28
• Rollover event — rollover sensors in the SRS ECU broadcast a crash signal to the PCU
• Kerb strike or severe pothole impact — very hard undercarriage impacts can occasionally trigger SRS crash thresholds on sensitive systems
• Airbag deployment — any airbag deployment will always set P1B28 as the SRS ECU fires its CAN crash message simultaneously with igniter circuits

False Triggers (No Collision)

• Faulty SRS ECU — an internal SRS ECU failure can cause it to broadcast a spurious crash message over CAN, triggering P1B28 without any impact
• Corroded or damaged SRS wiring — short circuits in airbag sensor wiring can generate false crash signals
• SRS crash sensor failure — a failed side impact or front impact sensor sending a continuous fault signal
• CAN bus corruption — in rare cases, severe CAN bus interference causes the PCU to misinterpret a data frame as a crash message
• Previous collision history not properly cleared — if a vehicle was previously in a collision and P1B28 was never properly reset with MUT-III, it will persist across ignition cycles indefinitely

Affected Mitsubishi Vehicles

Tools & Equipment Required

Step-by-Step Diagnosis

The diagnostic approach for P1B28 differs significantly depending on whether the vehicle has been in a collision. Follow this sequence:

• 1
  Establish Collision HistoryBefore connecting any diagnostic tool, visually inspect the vehicle for collision damage — front bumper, rear bumper, sills, wheel arches, and underbody. Check panel gaps, paint overspray, and misaligned body panels. A vehicle with P1B28 and no visible damage points to a false trigger; one with damage requires full post-collision HV inspection before any code clearing.
• 2
  Full Multi-Module ScanConnect MUT-III or equivalent and scan ALL modules — PCU, SRS/Airbag ECU, ECM, EV-ECU, ETACS, ABS/ASC. Record every DTC. The SRS module will contain the most diagnostic information — note which crash sensors triggered, whether airbags deployed, and the exact event timestamp in freeze frame data.
• 3
  Inspect HV Battery & Orange CablingRemove the service plug from the rear luggage area and wait 10 minutes before beginning. Visually inspect the HV battery tray beneath the vehicle for deformation, cracking, or electrolyte leakage. Inspect all orange HV cables for cuts, crushing, or abrasion. Check the main junction box connectors for burn marks or melting. Any physical damage to HV components means the vehicle must not be returned to service until those components are replaced.
• 4
  Investigate SRS DTCs for False TriggerIf no collision occurred and no HV damage is found, focus on the SRS module. Check for codes relating to specific crash sensors (front centre, left/right side impact, rollover). A faulty sensor storing a current fault alongside P1B28 is the most likely false trigger culprit. Check sensor connector integrity and wiring continuity with a DMM.
• 5
  Verify CAN Bus Between SRS and PCUIf all SRS sensors check out and no collision occurred, use a CAN oscilloscope to monitor the powertrain CAN bus during ignition. A corrupted or intermittent CAN signal from the SRS ECU can occasionally cause a false crash broadcast. Replace the SRS ECU if it is found to be broadcasting erratic data with no trigger.
• 6
  Clear P1B28 and Re-enable HV SystemOnly once the inspection is complete and all underlying faults are resolved, use MUT-III to clear P1B28 from the PCU and all remaining DTCs from the SRS module. Cycle the ignition, confirm no DTCs return, and verify HV system re-engagement in PCU live data — HV battery voltage should be present across the system bus and contactor status should read “Closed”.

Scanner Readout Explained

Below is a representative MUT-III diagnostic readout for a first-generation Outlander PHEV presenting with P1B28 following a low-speed rear impact that did not deploy airbags but did trigger the rear crash sensor threshold.

====================================================
  MITSUBISHI MUT-III SE — DIAGNOSTIC REPORT
====================================================
  Vehicle:     2018 Outlander PHEV (GG3W)
  VIN:         JMBXNGA3WJZ0XXXXX
  Date:        2025-02-21  14:17:44
  Technician:  Workshop Bay 1
====================================================

MODULE: PCU (PHEV Control Unit)
----------------------------------------------------
  P1B28  Crash Detection
         Status:       Confirmed / Current
         Freeze Frame:
           HV Battery SOC:        67%
           HV System Status:      ISOLATED
           Vehicle Speed:         8 km/h
           IG Status:             ON
           Contactor Status:      OPEN (Safety Isolation Active)

MODULE: SRS / Airbag ECU
----------------------------------------------------
  B1044  Rear Impact Sensor — Threshold Exceeded
         Status:       Confirmed / Historical
         Freeze Frame:
           Impact G-Force:        18.4G
           Airbag Deployment:     NO
           Event Timestamp:       2025-02-21  13:58:02

  B1005  SRS Warning Lamp Circuit — Illuminated
         Status:       Confirmed / Current

MODULE: ECM (Engine Control Module)
----------------------------------------------------
  No faults stored.

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

====================================================
  LIVE DATA SNAPSHOT (Key On, Engine Off)
====================================================
  HV Battery Voltage:          301.2V
  HV Battery SOC:              67%
  12V Auxiliary Battery:       12.7V
  HV Contactor (Main+):        OPEN
  HV Contactor (Main-):        OPEN
  HV Contactor (Pre-charge):   OPEN
  Inverter Temperature:        22°C
  SRS Crash Signal (CAN):      ACTIVE
  Front Motor (MG1) Speed:     0 RPM
====================================================

This readout clearly shows the PCU has isolated the HV system in direct response to the SRS crash signal. All three main contactors are open. The HV battery itself is healthy at 301.2V and 67% SOC — the isolation is entirely software-commanded, not a hardware failure. Once the SRS codes are cleared following inspection and the rear bumper structure is assessed, P1B28 can be cleared and the contactors will re-close on the next ignition cycle.

Step-by-Step Repair Guide

Repair Path A: Post-Collision — Inspection & Return to Service

• 1
  Complete All Bodywork & Structural RepairsRepair or replace all collision-damaged panels, crash structures, and subframe components before addressing the HV system. The vehicle must be structurally sound before HV re-enablement. If the HV battery tray has been deformed, replace the battery assembly — do not attempt to straighten or weld the tray.
• 2
  Replace Deployed Airbags & SRS ComponentsAny deployed airbag, pretensioner, or crash sensor that recorded an event must be replaced — these are single-use components. The SRS ECU must also be replaced if it recorded a deployment event, as its internal memory is permanently altered. Use only Mitsubishi OEM SRS components.
• 3
  Inspect & Reinstate HV CablesReinstall the service plug. Inspect all orange HV cables for damage along their full routed length. Verify connector torque specifications at the battery junction box, inverter, and motor connections. Any cable with damaged insulation must be replaced — do not tape or patch HV cabling.
• 4
  Clear All DTCs & VerifyUsing MUT-III, clear all DTCs across all modules — SRS, PCU, ECM, EV-ECU. Cycle the ignition and perform a full rescan. Confirm P1B28 does not return and that HV contactor status returns to “Closed” in PCU live data. Perform a short drive cycle to confirm normal PHEV operation.

Repair Path B: False Trigger — SRS Sensor or ECU Fault

• 1
  Identify the Faulty SRS SensorUse MUT-III to identify which crash sensor stored the fault. Disconnect the sensor connector and inspect for corrosion, moisture ingress, or mechanical damage. A sensor mounted in a previously repaired area (e.g. a bumper that was replaced after a minor prior incident) is a common culprit.
• 2
  Replace the Faulty SensorReplace the identified crash sensor with a Mitsubishi OEM part. Aftermarket SRS sensors are not recommended — sensitivity calibration must match the SRS ECU’s expectations precisely. Ensure correct orientation and secure mounting torque after installation.
• 3
  Clear All Codes & Confirm No RecurrenceClear all DTCs in SRS and PCU modules. Road test the vehicle over a variety of surfaces — including a speed bump at low speed — to confirm P1B28 does not re-trigger. Monitor live data during the test to verify SRS crash signal remains inactive.

Repair Cost Estimates

Prevention & Maintenance Tips

• Never ignore minor collision damage: Even a low-speed impact that does not deploy airbags can set P1B28 if the G-force threshold is exceeded. Always have the vehicle scanned after any impact, however minor.
• Inspect SRS sensor mounting points: During any bumper removal for parking sensor or camera work, check that SRS crash sensors are correctly remounted and torqued. A loose sensor can move and trigger falsely over rough roads.
• Protect orange HV cables during bodywork: If the vehicle goes to a bodyshop for any reason, ensure technicians are briefed on HV cable routing. A snagged or pinched orange cable during panel removal can cause damage that only manifests later.
• Verify pre-purchase scan on used PHEVs: Always include a full multi-module scan in any used Mitsubishi PHEV pre-purchase inspection. A cleared P1B28 with historical SRS data is a red flag for undisclosed collision history.
• Keep the service plug accessible: Ensure the rear luggage area service plug cover is not obstructed by cargo liners or aftermarket accessories. In a recovery situation, first responders and technicians need rapid access to HV isolation.

Frequently Asked Questions

Can I clear P1B28 myself with a generic OBD2 scanner?

No. P1B28 is stored in the PCU — a Mitsubishi-proprietary module that is not accessible via generic OBD2 readers. You will need a professional scanner with full Mitsubishi PHEV system coverage, such as MUT-III, Autel MaxiSYS, or Launch X431 PAD VII. Even with the right tool, P1B28 should only be cleared after a qualified inspection — not simply reset to restore drive power without understanding why it was set.

My car was not in an accident — why has P1B28 appeared?

This points to a false trigger. The most common causes are a faulty SRS crash sensor, corroded sensor wiring, a failing SRS ECU sending a spurious CAN message, or a very severe kerb or pothole impact that exceeded the crash sensor threshold without a collision. A full SRS module scan will usually identify the specific sensor or circuit at fault. The good news is that false-trigger P1B28 cases typically involve no HV hardware damage and are resolved by SRS sensor repair or replacement followed by a code clear.

Is it safe to clear P1B28 and drive the vehicle after a collision?

Only if a qualified HV technician has completed a full post-collision inspection and confirmed that the HV battery, orange cabling, contactors, and inverter are undamaged. Clearing P1B28 re-enables the HV system — if there is concealed HV hardware damage, this could create an electrocution or fire risk. This inspection is not optional. It must be carried out by a technician with recognised EV/HV training before the vehicle returns to service.

Will P1B28 prevent the petrol engine from starting?

Not necessarily. On first-generation Outlander PHEVs, the petrol engine uses the front generator motor (MG1) as a starter — this requires HV power. With HV isolated due to P1B28, the engine cannot be started. On some variants where a conventional 12V starter is also fitted as a backup, limited engine starting may be possible, but the vehicle still cannot drive under PHEV power with P1B28 active.

How long does a post-collision HV inspection take?

A thorough post-collision HV inspection by a trained technician typically takes 2–3 hours. This includes removing undertray panels to inspect the battery tray, tracing all orange cables along their full routed length, checking connector torque values, performing an insulation resistance test on the HV system, and completing the diagnostic scan. Do not accept a 30-minute “quick look” as a substitute for this full inspection.

Does P1B28 affect the 12V system or just the HV system?

P1B28 specifically commands isolation of the high-voltage system — the 300V+ traction battery and associated drive circuits. The 12V auxiliary system remains active, which is why the vehicle’s lights, instrument cluster, and infotainment typically continue to function normally even with P1B28 stored. This also means the diagnostic scanner can communicate with the vehicle’s modules even when HV is isolated.

Can a bodyshop clear P1B28, or does it need to go to a Mitsubishi dealer?

Any workshop with a capable professional scanner (Autel MaxiSYS, Launch X431 PAD VII, or similar) and a technician trained in HV vehicle inspection can perform the post-collision check and clear P1B28. It does not have to be a Mitsubishi dealer specifically, but the repairer must hold appropriate HV vehicle accreditation — such as IMI Level 3 Award in Electric/Hybrid Vehicle System Repair in the UK, or equivalent in your market. A standard bodyshop without HV training should not be clearing this code.

Can P1B28 return after being cleared?

Yes, in two scenarios. First, if a faulty SRS sensor or ECU was not replaced before clearing, the false trigger condition still exists and P1B28 will return — sometimes within the same drive cycle. Second, if the vehicle is subsequently involved in another impact that meets the crash threshold, the SRS ECU will again broadcast a crash message and P1B28 will be set again. A properly repaired vehicle with healthy SRS components should not see P1B28 return under normal driving conditions.

Conclusion

Mitsubishi P1B28 – Crash Detection is one of the most safety-critical codes in the Mitsubishi PHEV system, and deliberately so. It exists to protect vehicle occupants, first responders, and technicians from the dangers of a compromised 300V+ high-voltage system following a collision. When P1B28 is set after a genuine impact, it should be treated with the seriousness it deserves — a full HV and structural inspection is mandatory before the code is cleared and the vehicle returned to service.

In false-trigger scenarios, the resolution is typically straightforward — a faulty SRS crash sensor or corroded wiring is identified, replaced, and the code cleared without any HV hardware involvement. In either case, P1B28 is not a code to dismiss or reset blindly. The correct process, carried out by a competent technician with the right tools, protects both the vehicle and everyone who comes into contact with it.

Related Crash Detection Codes

Compare nearby crash detection trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0523 – Engine Oil Pressure Sensor/Switch ‘A’ High
• P0897 – Transmission Fluid Deteriorated
• P0896 – Shift Time Too Long
• P0895 – Shift Time Too Short
• P0893 – Multiple Gears Engaged
• P0884 – TCM Power Input Signal Intermittent