B1603 – DR Pretensioner Squib Short

The Mitsubishi fault code B1603 – Driver Seatbelt Pretensioner Squib Short Circuit is a manufacturer-specific diagnostic trouble code stored by the SRS (Supplemental Restraint System) airbag ECU on Mitsubishi vehicles. It indicates that the SRS control module has detected an abnormally low resistance — a short circuit — in the squib (pyrotechnic initiator) circuit of the driver seatbelt pretensioner. Unlike an open circuit fault, a short circuit on a squib circuit carries the additional concern of potential accidental deployment: an unintended current path through the squib could theoretically trigger the pretensioner without a collision event. The SRS warning light will be continuously illuminated and the fault must be treated as urgent.

What Does B1603 Mean on a Mitsubishi?

The SRS ECU continuously supplies a low-level monitoring current through each squib circuit and measures the resistance to confirm the circuit is within its calibrated window. For a typical Mitsubishi pretensioner squib, this window is narrow — usually in the range of 2.0–3.0 ohms. B1603 is stored when the measured resistance on the driver pretensioner squib circuit falls significantly below this minimum threshold, indicating that the two squib conductors have become bridged to each other (squib short), or that one or both conductors has shorted to vehicle ground or to another circuit. In all short circuit scenarios, the normal control path of the SRS ECU over the pretensioner is compromised — either the squib cannot receive the correct firing signal, or an uncontrolled current path exists that poses an accidental deployment risk.

Symptoms of B1603

B1603 presents with the following indicators:

• SRS warning light continuously illuminated on the instrument cluster
• B1603 stored in the SRS/airbag ECU when scanned with MUT-III or a compatible scanner
• Driver seatbelt pretensioner status compromised — deployment behaviour in a collision cannot be guaranteed
• Elevated risk of accidental pretensioner deployment due to the unintended low-resistance current path
• No driveability symptoms — B1603 is a purely electrical SRS fault
• Other SRS functions may remain operational, but the overall SRS system is flagged as degraded
• Potential roadworthiness failure in markets where a permanently illuminated SRS warning light is a testable item at inspection

Common Causes of B1603

• Chafed or pinched squib wiring with conductor-to-conductor contact — the two squib conductors bridging each other due to damaged insulation is the most common wiring cause of a short circuit reading
• Squib conductor shorting to vehicle body ground — harness insulation damaged at a routing clip, seat frame edge, or floor aperture allows one or both conductors to contact bare metal
• Corroded or contaminated SRS connector allowing cross-contact between adjacent pins — moisture or conductive debris bridging the squib pins inside the yellow SRS connector body
• Internal short within the pretensioner squib itself — the pyrotechnic initiator element develops an internal low-resistance fault without having deployed
• Incorrect aftermarket wiring or accessory installation — wiring routed beneath the driver seat or through the B-pillar area interfering with the SRS harness
• Damaged SRS ECU output stage — rare, but an internal ECU fault on the driver pretensioner squib drive circuit can present as an apparent short; the ECU is the last component to suspect
• Previously fired pretensioner with damaged residual wiring — a deployed pretensioner can leave burnt or fused wiring that produces a low-resistance reading

Common Misdiagnoses

• Pretensioner replaced without tracing the short to source: If the short is in the harness rather than the pretensioner unit itself, fitting a new pretensioner will not resolve B1603. The short must be isolated with a break-out box before any component is replaced.
• Short circuit tested with a standard multimeter across squib terminals: Probing squib terminals with an unregulated DMM is a recognised accidental deployment hazard on any squib circuit — but particularly so when a short circuit is suspected, as the circuit resistance is already abnormally low. Only approved SRS break-out boxes and resistance simulators should be used.
• SRS ECU replaced as first step: An internal ECU fault is the least likely cause of B1603. Full circuit isolation using a break-out box is mandatory before any module replacement is considered.
• Code cleared without repairing the short: B1603 is a current fault actively monitored on every ignition cycle. It returns immediately after clearing if the root cause has not been resolved — and the accidental deployment risk remains throughout.
• Connector cleaned without checking for conductive contamination between pins: Moisture or corrosion bridging adjacent pins inside the connector body is a specific short circuit cause that requires careful individual pin inspection, not just a general clean.

Affected Mitsubishi Vehicles

Model	Generation	Notes	Years
Outlander PHEV	GG/GF (1st Gen)	Driver pretensioner squib monitored independently; B1603 specific to driver circuit	2013–2021
Outlander PHEV	GN (2nd Gen)	Revised SRS architecture; same B1603 definition	2022–present
Outlander (non-PHEV)	GF/GG/ZJ/ZK/ZL	Driver pretensioner fitment confirmed across most market variants	2007–present
Eclipse Cross	GK/GL	Shares SRS module architecture with Outlander range	2017–present
ASX / RVR	GA/XD	Under-seat and B-pillar harness routing vulnerable on higher-mileage examples	2010–present
Galant Fortis / Lancer	CY/CZ	Market-specific SRS configurations — verify pretensioner type before diagnosing	2007–2017

Tools & Equipment Required

Tool	Purpose	Notes
Mitsubishi MUT-III / MUT-IV	SRS scan, live data, code clear	Required to confirm B1603 and verify repair
SRS break-out box / squib resistance simulator	Safe squib circuit resistance measurement and short isolation	Never use a standard DMM directly across squib terminals
Digital multimeter (DMM)	Harness continuity and insulation resistance checks	Only for harness segments with SRS connectors fully disconnected and shorting bars engaged
Wiring diagram (OEM)	Identify B1603 squib circuit routing for driver seat and B-pillar	Mitchell1 DIY or Mitsubishi FAST-II
Electrical contact cleaner & dielectric grease	SRS connector cleaning and pin isolation	Inspect each pin individually for conductive bridging
Trim and seat removal tools	Driver seat removal for harness access	Torx and hex set; plastic trim tools for B-pillar and seat rail covers

Step-by-Step Diagnosis

• 1
  Disable the SRS System Immediately — Before Any WorkSwitch off the ignition, remove the SRS fuse, and disconnect the battery negative terminal. Wait a minimum of 60 seconds before touching any SRS component, connector, or wiring. With a short circuit fault present, the risk of accidental deployment from a stray current is elevated — the SRS disable procedure is non-negotiable.
• 2
  Confirm B1603 with a Full SRS ScanReconnect power and use MUT-III or equivalent to read all stored SRS fault codes. Note whether B1603 is current or historical, and record any additional SRS codes that may indicate a shared wiring fault or a collision event that has already fired other SRS components in the driver circuit.
• 3
  Check for Prior Collision Evidence and Fired PretensionerInspect the driver seat, belt assembly, and B-pillar for signs of previous collision damage or repair. A fired pretensioner will have a fully retracted, locked belt that cannot be pulled out. Inspect the pretensioner housing for heat discolouration or gas discharge marks. If the pretensioner has fired, replacement is the required repair and the damaged wiring must also be inspected.
• 4
  Inspect the SRS Connector at the PretensionerWith SRS disabled, locate the yellow SRS connector at the driver pretensioner. Inspect the connector body for moisture, conductive corrosion deposits, or debris bridging adjacent pins. Inspect each individual pin for green oxidation or signs of arcing. A short caused by connector contamination is one of the quickest repairs — but only if the pins are thoroughly cleaned and individually verified clear of any bridging.
• 5
  Measure Squib Circuit Resistance with a Break-Out BoxConnect an approved SRS break-out box at the SRS ECU harness connector. Measure resistance on the driver pretensioner squib circuit. A reading significantly below 2.0 ohms with the pretensioner connected confirms an active short. Disconnect the pretensioner connector and re-measure — if the short clears, the pretensioner squib has failed internally or the connector was bridging. If the short remains in the harness with the pretensioner disconnected, the fault is in the wiring between the pretensioner and the SRS ECU.
• 6
  Trace the Squib Harness if the Short is in the WiringRoute out the pretensioner squib harness from the seat and B-pillar area back toward the SRS ECU, checking all sections for chafing against seat frame metalwork, pinching at routing clips, and any area where aftermarket wiring or accessories have been installed nearby. Use a DMM in insulation resistance mode — with all SRS connectors disconnected and shorting bars engaged — to identify which conductor is shorting and to which.

Scanner Readout Explained

====================================================
  MITSUBISHI MUT-III SE — DIAGNOSTIC REPORT
====================================================
  Vehicle:     2017 Outlander PHEV (GG3W)
  Date:        2025-03-27  09:14:33
====================================================
MODULE: SRS / AIRBAG ECU
----------------------------------------------------
  B1603  Driver Seatbelt Pretensioner Squib — Short Circuit
         Status:       Confirmed / Current
         Freeze Frame:
           Squib Circuit Resistance:   0.3 Ω (short detected)
           Expected Resistance Range:  2.0–3.0 Ω (typical squib spec)
           SRS Warning Lamp:          ON
====================================================
  LIVE DATA (SRS System Status)
====================================================
  Driver Front Airbag Squib:              OK
  Passenger Front Airbag Squib:           OK
  Driver Seatbelt Pretensioner Squib:     SHORT CIRCUIT — FAULT ACTIVE
  Passenger Pretensioner Squib:           OK
  Side Curtain L Squib:                   OK
  Side Curtain R Squib:                   OK
  Driver Knee Airbag Squib:              OK
====================================================
  NOTE: SRS system flagged as degraded.
  Driver pretensioner deployment behaviour
  in collision event cannot be guaranteed.
  Accidental deployment risk elevated.
====================================================

Step-by-Step Repair Guide

Repair Path A: Driver Pretensioner Unit Replacement

• 1
  Disable the SRS SystemRemove the SRS fuse and disconnect the battery negative terminal. Wait a minimum of 60 seconds. With a short circuit fault active, treat the pretensioner as a live and unstable pyrotechnic device until the SRS system is fully de-energised and the wait period has elapsed.
• 2
  Access the Pretensioner UnitDepending on the model year and pretensioner mounting location, access may require removal of the B-pillar lower trim, partial driver seat removal, or both. Refer to the OEM workshop manual for the correct trim removal sequence and fastener locations specific to your vehicle variant.
• 3
  Disconnect the Squib ConnectorLocate the yellow SRS connector at the pretensioner unit. Press the secondary lock release and disconnect carefully. The integrated shorting bar will engage on disconnection, shorting the squib terminals and eliminating any residual current path through the squib during the repair.
• 4
  Remove and Dispose of the Faulty UnitUnbolt the pretensioner from its anchor point. Handle carefully — even an unfired pretensioner with an internal short is a live pyrotechnic device. Follow local regulations for disposal. Do not attempt to disassemble or probe the unit internally under any circumstances.
• 5
  Fit the OEM Replacement UnitInstall the new OEM driver pretensioner and torque the anchor bolt to the workshop manual specification — pretensioner anchor torque is a safety-critical value. Reconnect the yellow SRS connector firmly until the secondary lock clicks fully and positively into place.
• 6
  Re-enable SRS, Clear the Code & VerifyRefit all trim and seat components to torque, reconnect the battery, and refit the SRS fuse. Use MUT-III to clear B1603 and run a full SRS system check. Confirm the SRS warning light extinguishes and that no further SRS codes are stored.

Repair Path B: SRS Harness Short Circuit Repair

• 1
  Isolate the Short Location in the HarnessWith SRS disabled and using an approved break-out box, confirm the short is present in the harness with the pretensioner disconnected. Segment-test the squib harness to narrow the fault to a specific run — from the pretensioner to the first intermediate connector, or from there to the SRS ECU. Use a DMM in insulation resistance mode with all SRS connectors disconnected to identify which conductor is shorting and to what.
• 2
  Locate and Repair the Damaged SectionTrace the harness in the identified segment. Common short circuit damage points are where insulation has chafed through against a seat frame edge, a routing clip, or a floor aperture, and where aftermarket wiring has been incorrectly routed alongside the SRS harness. Repair using an OEM-specification SRS harness repair kit — confirm with the workshop manual whether splice repairs are permitted on this specific squib circuit before proceeding.
• 3
  Verify Circuit Resistance, Re-enable SRS & ClearBefore refitting any trim or the seat, confirm the squib circuit resistance is within the specified window and that insulation resistance between conductors is within acceptable limits. Reconnect the battery and SRS fuse, clear B1603 with MUT-III, and confirm the SRS warning light extinguishes with no returning codes.

Repair Path C: SRS Connector Cleaning for Pin Bridging

• 1
  Disable SRS & Access the Pretensioner ConnectorFollow the full SRS disable procedure. Locate the yellow SRS connector at the driver pretensioner. Disconnect carefully and inspect the connector body under good lighting — look specifically for any conductive debris, moisture residue, or corrosion bridging between the squib pin cavities.
• 2
  Clean Pins Individually and Verify IsolationApply electrical contact cleaner to each pin cavity individually, ensuring any bridging deposit is fully removed. Allow to dry completely. Verify with a break-out box that pin-to-pin resistance in the connector is not artificially lowering the measured squib circuit resistance before reconnecting.
• 3
  Apply Dielectric Grease, Reseat & ClearApply dielectric grease to each pin face to prevent future moisture ingress. Reconnect the SRS connector — the secondary lock must click fully into position. Re-enable the SRS system, clear B1603 with MUT-III, and confirm the warning light extinguishes with no returning codes.

Repair Cost Estimates

Repair	Parts Cost (est.)	Labour (est.)	Total (est.)	DIY Difficulty
SRS connector cleaning — pin bridging	€0–€10	0.5 hr	€0–€60	Medium — SRS safety protocols essential
SRS harness short circuit repair	€10–€60	1–3 hr	€60–€280	Hard — requires SRS break-out box and wiring expertise
Driver pretensioner replacement (OEM)	€80–€280	1–2 hr	€130–€400	Hard — SRS specialist recommended
SRS ECU connector pin repair	€5–€30	1–2 hr	€55–€200	Hard — requires SRS break-out box

Prevention & Maintenance Tips

• Always follow the full SRS disable procedure before removing the driver seat — seat removal without disabling the SRS is the most preventable cause of disturbed squib wiring leading to short circuit faults
• Inspect driver seat and B-pillar SRS harness routing at every major service — chafing against seat frame metalwork develops gradually and is caught early by a visual inspection before the insulation fails completely
• Never route aftermarket wiring alongside the SRS squib harness — any contact between aftermarket cabling and the squib harness introduces a short circuit risk as insulation degrades over time
• Protect under-seat SRS connectors from moisture — apply fresh dielectric grease to all yellow SRS connector pin faces at each service interval to prevent conductive corrosion bridging
• Use OEM or OEM-equivalent pretensioner units only — non-standard units may present a squib resistance outside the SRS ECU calibration window and generate a new code immediately after installation
• Never ignore the SRS warning light — a short circuit squib fault is more urgent than an open circuit fault due to the elevated accidental deployment risk

Frequently Asked Questions

Can I drive my Mitsubishi with B1603 stored?

Technically the vehicle remains driveable, but a short circuit squib fault carries an elevated risk of accidental pretensioner deployment compared to an open circuit fault. The driver pretensioner could theoretically fire without a collision event while the short is present. The fault should be treated as urgent and the vehicle should be repaired as soon as possible rather than driven routinely with B1603 active.

Is a short circuit squib fault more dangerous than an open circuit fault?

Yes. An open circuit means the pretensioner simply cannot fire — the circuit is broken. A short circuit means an unintended low-resistance current path exists through or around the squib, which raises the possibility of accidental deployment from a stray current. Both are serious SRS faults, but B1603 should be treated with greater urgency than an equivalent open circuit code.

Can I test the squib circuit with my multimeter to find the short?

Not across the squib terminals directly. Using a standard DMM in ohms mode across squib terminals is a recognised deployment hazard under any SRS squib fault condition — and is particularly risky with a short circuit present, as the circuit is already in an abnormal low-resistance state. Use an approved SRS break-out box or squib resistance simulator. A standard DMM may be used to check insulation resistance between harness conductors only after all SRS connectors are disconnected and shorting bars confirmed engaged.

Will B1603 clear itself if the short is intermittent?

No. B1603 is stored in SRS ECU memory and must be actively cleared with MUT-III or a compatible scanner. If the short is intermittent — caused by a harness that only contacts bare metal at certain seat positions, for example — the code may not reappear immediately after clearing, but the underlying damage remains and the fault will return. An intermittent short is just as hazardous as a permanent one and requires the same thorough circuit tracing and repair.

Could an aftermarket seat heater or accessory cause B1603?

Yes. Aftermarket seat heater wiring routed beneath or through the driver seat without regard for SRS harness clearance is a recognised cause of squib short circuit faults. If B1603 appeared after an accessory installation, inspect the routing of all aftermarket wiring in the seat and B-pillar area before condemning any OEM SRS component.

Does the SRS ECU need replacing if B1603 returns after a new pretensioner and harness repair?

Only after full circuit verification has confirmed that the squib circuit resistance is within specification from the pretensioner connector all the way to the SRS ECU connector pins, and that insulation resistance between all conductors in the squib circuit is within acceptable limits. An internal ECU output stage fault is the least likely cause but cannot be excluded if all wiring and components check out correctly.

How long does a driver pretensioner replacement typically take?

For a technician with the correct workshop manual and tooling, the repair typically takes one to two hours depending on the trim access requirements for the specific model year. Code clearing and full SRS system verification with MUT-III adds a further 15–20 minutes. Vehicles requiring full seat removal for pretensioner access will sit toward the upper end of that estimate.

Conclusion

Mitsubishi B1603 – Driver Seatbelt Pretensioner Squib Short Circuit is a high-severity SRS fault that must be treated as urgent due to the elevated accidental deployment risk associated with a short circuit squib condition. The most common causes are chafed or pinched squib wiring, conductive contamination bridging the SRS connector pins, or an internal squib failure in the pretensioner unit. Always follow the full SRS disable procedure, use an approved break-out box to isolate whether the short is in the pretensioner, the harness, or the connector, replace faulty components with OEM parts only, and clear and verify with MUT-III.