B1405 on 2019-2021 Ford Transit: Airbag Light, Sagging Seat, and Repair Guide

What's Unique About the 2019-2021 Ford TRANSIT

Unlike many vehicles where this code might point to a random wiring issue or a faulty airbag module, the 2019-2021 Ford Transit has a well-documented design flaw affecting models built on or before February 11, 2021. The seat cushion's internal support structure, a suspension mat, is prone to failure. This failure directly leads to the sagging of the seat and subsequent damage to the integrated airbag system wiring, making it a highly specific and common problem for this platform. Ford has issued multiple Technical Service Bulletins (TSBs), such as TSB 24-2053, acknowledging this exact issue and providing a detailed repair procedure.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Illuminated airbag warning light on the dashboard.
• Noticeable sagging or a feeling of 'sinking' into the driver's seat cushion, often described as a 'smiley' or collapsed seat.
• Fault messages related to the restraint system on the instrument cluster display.
• The driver's seat may feel noticeably softer or less supportive than the passenger's seat.

Most Likely Causes

1. Damaged Seat Suspension Mat Assembly 🔴 High Probability A known issue on 2019-2021 Transits built on or before February 11, 2021, where the original mat design was weak and prone to breaking under normal use. The sagging seat then stresses and damages nearby airbag wiring.
   How to confirm: Visually inspect the driver's seat for sagging. A technician will remove the seat cushion cover to inspect the suspension mat and related wiring for visible damage, as outlined in Ford's TSBs.
   Typical fix: Replace the damaged suspension mat assembly with a revised repair kit from Ford (Part No. LK4Z-61632A22-C), which includes the new mat and additional support straps (Part No. LK4Z-6162948-A). 🎬 Watch this walkthrough of the seat spring and cushion replacement. Any damaged wiring or connectors must also be repaired or replaced.
   Est. part cost: $60-$100 for the repair kit and straps.
2. Damaged Airbag Wiring Harness 🟡 Medium Probability The wiring harness is routed within the seat assembly and can be chafed, stretched, or broken as a direct result of the suspension mat failure and seat sagging. The constant movement of the unsupported seat puts strain on the wires.
   How to confirm: After removing the seat cushion, perform a visual inspection of all wiring under the seat and leading to the side airbag. Check for pinched, frayed, or broken wires and test for continuity with a multimeter. TSB 24-2053 specifically instructs to inspect the seat airbag deployment circuit for damage.
   Typical fix: Repair the specific damaged wire(s). In severe cases where the wiring is damaged close to the airbag, the entire side airbag assembly (which includes a wiring pigtail) may need to be replaced.
   Est. part cost: $5-$250, depending on whether a simple wire repair is needed or if a harness/airbag assembly is required.

Rare But Worth Checking

• Faulty Restraints Control Module (RCM): This is very unlikely compared to the seat issue. The RCM should only be suspected if the seat structure and all related wiring have been thoroughly inspected and found to be in perfect condition.
• Loose Connector Under Seat: Items stored under the seat or passengers' feet can sometimes knock connectors loose. While less common for this specific code which is tied to a known TSB, it's a simple check worth performing.

Diagnosis Steps

1. Scan the Restraints Control Module (RCM) for all Diagnostic Trouble Codes (DTCs). Confirm B1405 is present, and note any other codes listed in TSB 24-2053.
2. Visually inspect the driver's seat. Does it feel softer than the passenger seat? Is there visible sagging or a lack of support?
3. Check the vehicle build date. This issue primarily affects Transits built on or before February 11, 2021.
4. Following safety procedures to depower the SRS system, disconnect the battery and wait at least one hour before 🎬 Watch this guide on handling airbag sensors during seat installation. working on any airbag components.
5. Remove the driver's seat from the vehicle for inspection. This typically involves removing four T40 Torx bolts from the seat tracks.
6. Remove the seat cushion upholstery to gain access to the internal components. This involves cutting hog rings or releasing 🎬 See how to properly disassemble and repair the lower cushion. velcro attachments.
7. Inspect the suspension mat assembly for broken plastic or metal components. The failure will be obvious.
8. Carefully inspect the airbag wiring harness that is attached to or runs near the suspension mat. Look for any signs of stretching, pinching, or broken wires, as shown in the TSB figures.
9. If damage is found, proceed with the repair outlined in TSB 24-2053 or its successors. This involves installing the new mat and adding reinforcement straps.
10. If no physical damage is found, perform electrical checks (continuity, resistance, short to ground/power) on the B1405 circuit between the RCM and the airbag connector.

Parts You'll Likely Need

• Front Seat Cushion Repair Kit (OEM #LK4Z-61632A22-C) — This is the official Ford kit designed to fix the root cause of the problem, containing the redesigned suspension mat.
  Trusted brands: Motorcraft
  OEM price range: $60-$90
  Aftermarket price range: N/A
• Front Seat Cushion Strap (OEM #LK4Z-6162948-A) — These additional straps are part of the TSB repair procedure to provide extra support and prevent future sagging. The TSB specifies that two are required for the repair.
  Trusted brands: Motorcraft
  OEM price range: $15-$30
  Aftermarket price range: N/A
• Side Airbag Assembly (OEM #CK4Z-14611D10-A) — Only needed if the wiring harness attached to the airbag itself is damaged beyond repair during the suspension mat failure. The TSB provides specific part numbers for standard and swivel seats.
  Trusted brands: Motorcraft
  OEM price range: $150-$250
  Aftermarket price range: N/A

Related Codes That Often Appear With This One

• B1408 — This code is for the passenger-side equivalent or another part of the same airbag circuit and is listed in the same TSBs for the seat sagging issue.
• B1407 — Also related to the passenger side airbag deployment control and cited in the TSBs.
• B0001 — Relates to the driver's frontal airbag and can be triggered along with other RCM faults. It is mentioned in the TSBs for the seat issue.
• B0010 — Relates to the passenger's frontal airbag and is also mentioned in the TSBs for the seat issue.
• B1404 — Another driver-side deployment control code listed in the TSBs related to the seat sagging problem.

Technical Service Bulletins (TSBs) & Recalls

• TSB 24-2394: Notes that vehicles may exhibit front seat cushion sagging and store DTC B1405 in the RCM.
• TSB 25-2182: Links a sagging driver seat cushion and DTC B1405 to a damaged suspension mat assembly.
• TSB 24-2053: Provides the detailed service procedure to correct the condition by replacing the suspension mat and adding reinforcement straps. It specifies part numbers and labor times (1.0 hr for one seat).

Platform-Specific Known Issues

• TSB 24-2053 (supersedes 23-2235): Ford has issued multiple technical service bulletins for 2019-2021 Transit models concerning a sagging front seat cushion that leads to an illuminated airbag light with code B1405 (and others). The official repair involves replacing the seat's internal suspension mat and installing two additional webbing strap assemblies to the seat frame for reinforcement.
• Owner Experience: Owners on forums describe the issue as a sudden failure where the seat feels like it has collapsed. The repair is often covered under warranty if the vehicle is within the warranty period, but can be a several hundred dollar repair at a dealership otherwise.

Mechanic-Grade Diagnostic Values

• Airbag Deployment Circuit Resistance — expected: 1.44 to 3.52 ohms. Failure: A reading outside this range will trigger a DTC. Values below 1.44 ohms indicate a short, while values above 3.52 ohms indicate an open circuit or high resistance.
• Live Data PID for Left Side Air Curtain — expected: Monitor PID DEPLOY_11_R on a Ford-specific scan tool. The value should remain stable within the 1.44 to 3.52 ohm range.. Failure: Fluctuations or values outside the specified range, especially while wiggling the seat harness, point to an intermittent connection or damaged wire.

Hidden / Shadow Codes Worth Checking

• B1405:11: Driver Side Curtain Deployment Control - Short to Battery (see via Ford IDS or equivalent professional scan tool capable of reading manufacturer-specific fault type identifiers.)
• B1405:12: Driver Side Curtain Deployment Control - Short to Ground (see via Ford IDS or equivalent professional scan tool capable of reading manufacturer-specific fault type identifiers.)
• B1405:13: Driver Side Curtain Deployment Control - Open Circuit (see via Ford IDS or equivalent professional scan tool capable of reading manufacturer-specific fault type identifiers.)
• B1405:1A: Driver Side Curtain Deployment Control - Resistance Below Threshold (see via Ford IDS or equivalent professional scan tool capable of reading manufacturer-specific fault type identifiers.)

Scan Tool Commands That Help

• Ford IDS (or equivalent): View Live Data PID: DEPLOY_11_R — Use this to monitor the real-time resistance of the driver's side curtain airbag circuit. Wiggling the seat and harness while watching this PID can confirm an intermittent open or short caused by the sagging seat issue.
• Ford IDS (or equivalent): RCM Self-Test (On-Demand) — This is the initial step to confirm if the fault is currently active (on-demand) or intermittent (continuous memory only).
• Ford IDS (or equivalent): Module Programming / As-Built Data Configuration — This function is required only if the Restraints Control Module (RCM) is replaced. It configures the new module to the vehicle's specific options.
• Ford IDS (or equivalent): SRS Verification Test — This procedure should be run after any SRS component repair or replacement to verify the entire system is functioning correctly and to clear any stored DTCs.

Wiring & Ground Locations

• Restraints Control Module (RCM) — Located on the vehicle floor, underneath the handbrake assembly, between the driver and passenger seats.. This is the module that monitors the airbag circuits and stores the B1405 code. Access requires removing the driver's seat and potentially the battery box and handbrake assembly to test wiring directly at the module.
• Driver's Seat Main Connector — Underneath the driver's seat.. This is the primary connector for all electronics in the seat, including the airbag circuit. It's a critical point for checking continuity and resistance between the seat harness and the body harness. It can be dislodged by items under the seat.
• B-Pillar Ground Point — Located on the B-Pillar, often near the D-ring for the seatbelt.. While not directly cited for the SRS, this is a major chassis ground point. A poor ground connection here can cause unpredictable electrical issues in various body-related modules.

OEM Part Supersession History

• TSB 21-2353 → TSB 22-2263, then TSB 24-2053 — Updates to the service procedure for correcting the front seat cushion sagging.
  Heads up: Always use the latest TSB for the most current repair instructions and part numbers.

Model Year Variations Within This Range

• 2020-2021: The 2020 model year introduced a significant refresh including a new dashboard design with an optional 8-inch SYNC 3 screen, new powertrain options (new base 3.5L PFDi V6, optional 2.0L EcoBlue Diesel, 10-speed automatic transmission), and available All-Wheel Drive. Optional swivel seats were also introduced, which may have different wiring harnesses than standard seats.
• 2019 - Early 2021: The seat suspension mat issue is specific to Transits built on or before February 11, 2021. Vehicles built after this date should have the updated seat structure from the factory.