B1499 – Control Unit Collision Decision

Fault code B1499 on Mitsubishi vehicles signals that the Supplemental Restraint System (SRS) control unit has detected a malfunction within its internal collision decision circuitry — the core processing logic that determines whether a crash event meets the threshold to deploy airbags and pre-tensioners. This is not a peripheral sensor fault; the problem lies inside or directly connected to the SRS ECU itself, making it one of the most safety-critical DTCs a Mitsubishi owner can encounter. With B1499 present, the airbag system may be fully or partially disabled, and driving until the fault is resolved is strongly inadvisable.

What Does B1499 Mean?

The B1499 code is a Mitsubishi manufacturer-specific (B1xxx) fault stored in the SRS/airbag control unit. The term “control unit collision decision” refers to the internal algorithm and associated hardware — typically ASIC chips, microprocessors, and safing sensor logic — that the SRS ECU uses to evaluate crash severity data and make a binary deploy/no-deploy decision in milliseconds during a collision event.When B1499 is set, the SRS ECU has performed a self-diagnostic check and found that this decision-making circuit has produced an out-of-range result, failed an internal continuity test, experienced a voltage anomaly, or suffered an internal hardware fault. In practical terms, the module cannot guarantee it will correctly deploy restraints in a real crash — or, equally dangerous, that it won’t deploy unexpectedly. The SRS warning lamp will illuminate and remain on, and the system typically enters a fail-safe state that disables all airbag deployment.Because the collision decision circuit is internal to the SRS ECU, B1499 most commonly points to a failed control module rather than a wiring or sensor problem upstream. However, power supply faults, ground integrity issues, and prior crash events that partially damaged the ECU without triggering full deployment are also documented triggers.

Symptoms

• SRS / airbag warning light illuminated and will not extinguish after engine start
• All airbags and seat-belt pre-tensioners disabled (system in fail-safe mode)
• Inability to clear B1499 with a generic OBD2 scanner — SRS-capable tool required
• Multiple additional SRS codes may accompany B1499 (B1000, B1001, or internal ECU codes)
• Seatbelt pre-tensioner warning may also activate on some Mitsubishi models
• No outward drivability symptoms — engine, transmission, and ABS operate normally
• Possible intermittent SRS light cycling on and off in early-stage ECU failure

Common Causes

• Failed SRS ECU / airbag control module — internal hardware fault within the collision decision ASIC or microprocessor; the most frequent root cause
• Prior collision event — the vehicle was involved in a crash that registered g-force above the safing threshold, partially triggering internal ECU logic without full deployment; ECU may be permanently latched
• Corroded or poor ground connection at the SRS ECU — high resistance on the ECU ground path corrupts the internal voltage reference used by collision decision circuitry
• Low or unstable battery voltage — the SRS ECU requires stable supply voltage; a weak battery or charging fault can cause the collision decision circuit to log internal errors
• Water or moisture ingress into the SRS ECU connector — pin corrosion on the ECU main harness connector introduces resistance or shorts that trigger internal fault detection
• Faulty SRS ECU main harness connector — spread, bent, or backed-out pins on the multi-pin connector at the module itself
• Prior improper airbag system repair — incorrect reset procedures or non-Mitsubishi replacement parts may leave the ECU in a locked fault state

Common Misdiagnoses

• Replacing crash sensors or clock spring first — B1499 is an internal ECU fault, not an upstream sensor code; replacing peripheral components will not resolve it
• Attempting to clear with a generic OBD2 scanner — B1499 is stored in the SRS module, which requires a manufacturer-level or SRS-capable bi-directional scanner; generic tools often cannot even read this fault
• Blaming the battery alone — while low voltage can contribute, a battery replacement without diagnosing the ECU will allow the code to return immediately
• Assuming a post-collision ECU can be reset — if the vehicle was in a crash that crossed the ECU’s internal deployment threshold, the SRS ECU may be permanently latched and require replacement regardless of whether airbags physically deployed
• Overlooking a second-hand or salvage ECU without proper VIN/variant matching — fitting an SRS ECU from a different Mitsubishi variant or model year without correct coding will generate B1499 and related internal faults

Affected Vehicles

Make	Model	Years	Notes
Mitsubishi	Outlander	2003–2023	All generations; ECU location varies by gen
Mitsubishi	Lancer / Lancer Evolution	2002–2017	Including Evo VIII–X; high-g driving can latch ECU
Mitsubishi	Eclipse / Eclipse Cross	2000–2022	Eclipse Cross (2018+) uses updated SRS ECU variant
Mitsubishi	Galant	2000–2012	Older platforms most susceptible to ground corrosion
Mitsubishi	Pajero / Montero	2000–2021	4WD use and vibration can accelerate connector wear
Mitsubishi	ASX / RVR	2010–2023	Shared platform with Outlander Sport
Mitsubishi	L200 / Triton	2005–2023	Work truck environments increase moisture ingress risk

Tools & Equipment

Tool	Purpose	Notes
Mitsubishi MUT-III or MUT-III Neo	OEM SRS diagnostics, live data, ECU identification	Required for accurate B1499 diagnosis and ECU programming
Bi-directional SRS scanner (Launch X431, Autel MaxiSYS)	SRS fault reading/clearing, module ID	Must support Mitsubishi SRS protocol; generic OBD2 insufficient
Digital multimeter (DMM)	Battery voltage, ground resistance, connector continuity	Use 4-wire Kelvin method for ground resistance measurement
Battery support unit / maintainer	Stable voltage during SRS ECU work	Mandatory — SRS ECU must not lose power mid-procedure
Connector inspection kit (pick set, contact cleaner)	ECU harness connector pin inspection and cleaning	Inspect all pins before condemning ECU
Torque screwdriver / trim removal tools	ECU access (under centre console or beneath seats)	Location varies by model; consult workshop manual
Workshop manual (OEM or Mitchell1 DIY)	ECU connector pin diagrams, ground locations, replacement procedure	Essential for correct pin-out and replacement coding steps

Step-by-Step Diagnosis

• 1
  Safety preparation — disable the SRS systemDisconnect the negative battery terminal and wait a minimum of 60 seconds before working near any SRS component or connector. The SRS backup capacitor must fully discharge. Do not skip this step — accidental airbag deployment can cause serious injury.
• 2
  Connect an SRS-capable scanner and retrieve all fault codesReconnect the battery, then use a Mitsubishi MUT-III or compatible SRS scanner to read all codes stored in the airbag control module. Record every code present. B1499 appearing alongside B1000 or B1001 (internal ECU power faults) strongly indicates an ECU hardware failure rather than a wiring issue.
• 3
  Check crash history and deployment statusUse the scanner to query whether the SRS ECU has logged a deployment event or latched crash data. Check the vehicle history for any prior collision records. If the ECU shows a recorded crash event, it is permanently locked and must be replaced — no reset procedure will clear a post-deployment latch.
• 4
  Verify battery voltage and charging systemWith the engine running, measure battery voltage at the battery terminals (should be 13.8–14.4 V). At rest, battery should hold above 12.4 V. Use the DMM to check the SRS ECU main power supply fuse and its feed wire. Voltage drop exceeding 0.5 V on any feed or ground circuit is a fault.
• 5
  Inspect the SRS ECU ground pointsLocate all SRS ECU ground connections (refer to the workshop manual for exact locations — typically body ground studs near the centre console or under the seat). With the battery disconnected, measure resistance between each ground terminal and clean chassis metal. Resistance above 0.5 ohms indicates a corroded or loose ground that must be cleaned and re-torqued.
• 6
  Inspect the SRS ECU harness connectorCarefully disconnect the main harness connector at the SRS ECU. Inspect every pin cavity for corrosion, moisture, spread pins, or backed-out terminals. Apply electrical contact cleaner, allow to dry fully, and reseat the connector firmly. Reconnect the battery, clear codes, and recheck — if B1499 returns immediately, the ECU itself is the fault.
• 7
  Confirm ECU fault and plan replacementIf all power, ground, and connector checks pass and B1499 persists, the SRS ECU has an internal hardware fault. Document the existing ECU part number and variant code using the scanner before removal — replacement units must match exactly. Proceed to the repair guide below.

Scanner Readout Explained

System: SRS / Airbag Control Unit DTC: B1499 Status: Current / Stored Description: Control Unit Collision Decision — Internal Circuit MalfunctionFreeze Frame Data (where available): Battery Voltage at Set: [11.4 V — below-spec supply noted] Crash Event Logged: [YES / NO] Deployment Status: [DEPLOYED / NOT DEPLOYED] ECU Internal Status: [FAULT — collision decision circuit]Related Codes Often Present: B1000 — SRS ECU internal power supply fault B1001 — SRS ECU internal voltage reference fault B1005 — SRS ECU internal ROM/RAM errorReadiness: Airbag Deployment: DISABLED (fail-safe active) Pre-tensioners: DISABLEDAction Required: Clear attempt: Code will NOT clear if crash event latched or ECU hardware failed Recommended next step: ECU ground / power verification → ECU replacement if fault persists

Step-by-Step Repair Guide

Repair Path A — Power Supply / Ground Fault Correction

Follow this path when diagnosis confirms low battery voltage, a failed charging system, or a high-resistance ground at the SRS ECU.

• 1
  Replace the battery if below specificationIf battery open-circuit voltage is below 12.4 V or a load test fails, replace the battery with a unit meeting Mitsubishi’s CCA and capacity specification for the model. Do not attempt SRS diagnosis with a weak battery in circuit.
• 2
  Clean and re-torque all SRS ECU ground pointsUsing the workshop manual ground location chart, remove each SRS ECU ground bolt, clean the contact surface with a wire brush or abrasive pad down to bare metal, apply anti-corrosion compound, and re-torque to specification (typically 6–10 Nm). Re-measure resistance — target below 0.1 ohms.
• 3
  Clear codes and verifyReconnect the battery using a battery support unit to maintain stable voltage during the procedure. Use the SRS scanner to clear B1499. Perform a full ignition cycle and rescan. If B1499 does not return and the SRS warning lamp extinguishes, the repair is complete. If it returns, proceed to Repair Path B.

Repair Path B — SRS ECU Replacement

Follow this path when B1499 persists after power and ground verification, or when a crash event is confirmed latched in the existing ECU.

• 1
  Disable SRS and source a matched replacement ECUDisconnect the battery and wait 60 seconds minimum. Source a new or remanufactured SRS ECU that exactly matches the original part number and variant code — do not fit a unit from a different model year or body variant without confirming compatibility with Mitsubishi parts documentation.
• 2
  Remove the faulty SRS ECUFollow the workshop manual procedure for your specific model to access and remove the SRS ECU (typically beneath the centre console or under the front seat). Disconnect the harness connector(s) carefully, noting any locking tab mechanism. Remove mounting bolts and extract the unit.
• 3
  Install the replacement ECUMount the new ECU in the OEM location, torque the mounting bolts to specification, and firmly seat the harness connector until the locking tab engages with an audible click. Do not force or cross-thread any fastener.
• 4
  Perform ECU initialisation and variant coding if requiredSome Mitsubishi SRS ECU replacements require variant coding or initialisation via the MUT-III scanner after fitment. Connect the MUT-III, navigate to SRS ECU programming, and follow the on-screen procedure. Skipping this step on models that require it will result in a new fault code being generated immediately.
• 5
  Clear all SRS codes and perform a full system verificationUse the SRS scanner to clear all stored codes. Perform a complete ignition cycle (key off → key on → engine running → key off). Rescan the SRS module — no faults should be present. Confirm the SRS warning lamp extinguishes within the normal lamp-test period on startup. Road-test the vehicle and rescan to confirm no codes return.

Repair Cost Estimates

Repair	DIY Cost	Workshop Cost	Notes
Battery replacement	£80–£130 / $90–$150	£120–£180 / $140–$210	Only applicable if battery is confirmed faulty
SRS ECU ground cleaning and re-torque	£5–£15 / $5–$20	£60–£100 / $70–$120	Materials only for DIY; labour-light job
SRS ECU replacement (new OEM)	£350–£650 / $400–$750	£550–£950 / $650–$1,100	OEM unit pricing; includes programming where required
SRS ECU replacement (remanufactured)	£150–£300 / $170–$350	£300–£550 / $350–$650	Verify reman unit includes variant coding; check warranty
SRS ECU programming / variant coding (labour only)	N/A — requires MUT-III	£60–£120 / $70–$140	Required on some models after replacement

Prevention & Maintenance Tips

• Keep the battery in good condition — test it annually and replace at the first sign of weakness; an SRS ECU is highly sensitive to supply voltage fluctuations
• After any collision — even a minor parking impact — have the SRS system scanned for stored crash data before assuming no damage occurred
• Never allow water to pool under seats or around the centre console where the SRS ECU is typically mounted; address door seal, sunroof drain, or carpet water ingress promptly
• When purchasing a used Mitsubishi, always scan the SRS module before buying — a latched crash event in the ECU represents a significant safety and cost liability
• Avoid using non-OEM or uncoded replacement SRS ECUs; always confirm part number, variant code, and whether the replacement unit requires MUT-III programming
• Include SRS module scanning as part of your regular service schedule — catching early-stage internal codes before they become critical failures can prevent a full ECU replacement
• Ensure all bodywork and underbody repairs re-establish factory ground paths — cutting corners on ground strap reconnection after panel work is a documented cause of SRS faults on Mitsubishi vehicles

Frequently Asked Questions

Can I drive my Mitsubishi with a B1499 code active?

Technically the vehicle will start and drive, but doing so is strongly inadvisable. With B1499 active, the SRS ECU has entered fail-safe mode and disabled the entire airbag and pre-tensioner system. In a collision, no airbags will deploy and seat-belt pre-tensioners will not activate, significantly increasing the risk of serious injury. Resolve the fault before returning the vehicle to regular use.

Will a generic OBD2 scanner read or clear B1499?

Not reliably. B1499 is stored in the SRS control module, which is a manufacturer-specific (non-powertrain) module that most generic OBD2 scanners cannot communicate with. You need a scanner that explicitly supports Mitsubishi SRS diagnostics — such as the MUT-III, Autel MaxiSYS, or Launch X431 with Mitsubishi SRS coverage — to read, interpret, and clear this code.

My Mitsubishi was in a minor accident and B1499 appeared. Do I need a new ECU?

Possibly yes. The SRS ECU records crash data when deceleration forces exceed its internal threshold, even if airbags did not physically deploy. If the scanner confirms a crash event is latched in the ECU, the module is permanently locked and cannot be reset by any clearing procedure — replacement is the only resolution. This is a deliberate safety design to ensure a compromised ECU is not returned to service.

Can I fit a used SRS ECU from a salvage yard to save money?

This carries significant risk. A salvage ECU may already have a latched crash event that will immediately generate B1499 in your vehicle. It must also exactly match your vehicle’s part number and variant code, and may require MUT-III programming to initialise. If you choose this route, verify the unit’s history thoroughly and have it programmed by a Mitsubishi dealer or specialist before assuming it is serviceable.

How long does SRS ECU replacement take?

Physical ECU removal and installation typically takes 1–2 hours depending on the model and ECU location. On models requiring post-fitment variant coding via MUT-III, add 30–60 minutes for the programming procedure. Total workshop time is usually quoted as 2–3 hours including diagnostic confirmation and post-repair verification scanning.

Why does B1499 sometimes appear alongside multiple other SRS codes?

When the SRS ECU’s internal collision decision circuit fails, it can cascade into related internal fault codes such as B1000 (internal power supply), B1001 (internal voltage reference), or B1005 (ROM/RAM integrity). These are all symptoms of the same root cause — ECU hardware failure — rather than separate independent faults. Resolving the root cause (ECU replacement or power supply correction) will typically clear all of them simultaneously.

Is B1499 covered under any Mitsubishi recall or warranty extension?

There is no universal Mitsubishi recall specifically covering B1499 at the time of writing. However, some earlier Mitsubishi models were subject to Takata airbag inflator recalls that involved SRS system inspection and repair — vehicles serviced under those recalls may have had SRS ECU work performed. Check your VIN against the current Mitsubishi recall database and consult your national road safety authority’s recall lookup tool to confirm whether any open campaigns apply to your specific vehicle.

Can a bad clock spring cause B1499?

A faulty clock spring (spiral cable) will typically generate specific codes related to the driver’s airbag squib circuit — such as B1200 or B1201 — rather than B1499. The collision decision circuit referenced by B1499 is internal to the SRS ECU itself, not in the external sensor or deployment circuit wiring. If the clock spring is also at fault, you will likely see additional codes alongside B1499, but the clock spring is not the cause of B1499 and replacing it will not resolve this specific code.

Conclusion

B1499 — Control Unit Collision Decision — is one of the most serious SRS fault codes a Mitsubishi owner can encounter. Because it reflects a failure within the airbag ECU’s core deployment logic rather than a peripheral sensor or wiring fault, the diagnostic path is relatively focused: verify power supply integrity, confirm ground quality, inspect the ECU connector, and check for a latched crash event. In the majority of confirmed cases, the SRS ECU itself requires replacement. Given the direct relationship between a functioning SRS system and occupant safety in a collision, this is a fault that demands prompt, professional attention — do not delay resolution or continue driving with the SRS warning lamp illuminated.