B1408 on 2019-2021 Ford Transit: Airbag Light and Seat Sagging Causes & Fixes

What's Unique About the 2019-2021 Ford TRANSIT

This is a well-documented, platform-specific failure on 2019-2021 Transit vans built on or before February 11, 2021. Ford has issued a series of superseding Technical Service Bulletins (TSBs) acknowledging that the original driver's seat suspension mat is prone to cracking and damage. This failure simultaneously causes the seat cushion to sag and triggers the airbag warning light with code B1408. The issue is so common that Ford has created a specific repair kit (Part No. LK4Z-61632A22-C) and a detailed service procedure to address it, which includes adding reinforcing straps.

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.
• Driver's seat cushion feels like it is sagging, collapsed, or has lost support, especially on the side bolster.
• Audible chimes accompanying the warning light.
• Wrinkles developing on the seat cover fabric due to the lack of underlying foam support.

Most Likely Causes

1. Damaged Driver's Seat Suspension Mat Assembly 🔴 High Probability Ford has issued multiple TSBs (including TSB 25-2182, TSB 24-2394, and TSB 24-2053) for this specific failure on 2019-2021 models built on or before February 11, 2021, indicating a design or material flaw. The plastic mat cracks around its mounting points, severing the integrated SRS wiring and causing the seat to collapse. This is especially common in high-use commercial vehicles.
   How to confirm: Visually inspect the driver's seat for sagging. Scan the Restraints Control Module (RCM) for code B1408 and other related codes listed in the TSBs. The presence of both symptoms is a strong confirmation.
   Typical fix: Replace the suspension mat assembly and install two additional webbing strap assemblies as per the procedure in the relevant TSB. This is sold as a kit (LK4Z-61632A22-C).
   Est. part cost: $430-$660
2. Damaged Wiring or Connectors Under Seat ⚪ Low Probability Wiring under seats is susceptible to damage from items stored under the seat or from repeated seat movement, especially after a seat swap or installation of a swivel base.
   How to confirm: Visually inspect the main yellow wiring harness and connectors under the driver's seat for any signs of pinching, chafing, or disconnection. A Reddit user reported their airbag light after a swivel seat install was due to a connector not being fully screwed in.
   Typical fix: Repair the damaged section of the wiring harness or clean and re-secure the connector. After repair, the code may need to be cleared with a capable scan tool.
   Est. part cost: $5-$50

Rare But Worth Checking

• Faulty Restraints Control Module (RCM): This is extremely rare for this specific code on this vehicle. The RCM should only be suspected after the seat suspension mat and all related wiring have been definitively ruled out. A faulty RCM often presents with different codes, like U3000.

Diagnosis Steps

1. Confirm the airbag warning light is on.
2. Use an OBD-II scanner capable of reading SRS codes (like FORScan for Fords) to scan the Restraints Control Module (RCM). Confirm B1408 is present.
3. Check for the presence of related codes: B1405, B1407, B0001, B0010, and/or B1404.
4. Visually and physically inspect the driver's seat cushion for a sagging or collapsed feeling. Compare it to the passenger seat.
5. Carefully inspect the wiring and connectors under the driver's seat, especially the main yellow connector. Look for any signs of damage, stretching, or loose connections.
6. If the seat is sagging and code B1408 (or a related code) is present, the cause is almost certainly the suspension mat assembly, as detailed in Ford TSBs 25-2182, 24-2394, and 24-2053.
7. Follow the service procedure outlined in the TSB to replace the seat cushion repair kit. This is a complex job involving seat removal and disassembly and is best left to a professional unless you are experienced.

Parts You'll Likely Need

• Front Seat Cushion Repair Kit (OEM #LK4Z-61632A22-C) — This is the specific part kit released by Ford to fix the known issue of a failing seat suspension mat that causes code B1408. It includes the new mat assembly.
  Trusted brands: Motorcraft
  OEM price range: $432-$661
  Aftermarket price range: N/A
• Front Seat Cushion Strap (OEM #LK4Z-6162948-A) — The TSB repair procedure requires installing two of these additional straps to reinforce the new seat structure. They must be ordered separately.
  Trusted brands: Motorcraft
  OEM price range: $15-$30
  Aftermarket price range: N/A

Related Codes That Often Appear With This One

• B1405 — This code is listed in the same TSBs and points to the same faulty seat suspension mat assembly.
• B1407 — Also listed in the TSBs for the driver's seat suspension mat failure.
• B0001 — Another code specified in the TSBs related to the driver's side restraints system failure due to the seat mat.
• B0010 — Also specified in the TSBs for the same seat mat issue.
• B1404 — Listed in the TSBs as another potential code set by the failing seat suspension mat.

Technical Service Bulletins (TSBs) & Recalls

• TSB 25-2182: The most recent bulletin, which supersedes TSB 24-2394. It confirms the link between a sagging driver's seat, DTC B1408 (and others), and a damaged suspension mat assembly.
• TSB 24-2394: Linked DTC B1408 with a sagging front seat cushion in models built before 11-Feb-2021.
• TSB 24-2053: Superseded a previous TSB and provides the service procedure to replace the suspension mat and add webbing straps to correct the condition causing B1408.
• TSB 23-2235: An earlier version of the bulletin, also linking B1408 to the sagging seat cushion and the providing a repair procedure.
• TSB 22-2263: An even earlier version that also details the issue and the repair involving the mat and straps.

Platform-Specific Known Issues

• A series of Technical Service Bulletins (TSB 25-2182, TSB 24-2394, TSB 24-2053, TSB 23-2235, TSB 22-2263) have been issued by Ford for 2019-2021 Transit models built on or before February 11, 2021, for a sagging driver's seat cushion that triggers airbag DTCs, including B1408.

Hidden / Shadow Codes Worth Checking

• B1408:13: The ':13' suffix indicates a 'Circuit Open' fault. This is the specific failure mode the RCM detects when the wiring within the driver's seat suspension mat breaks, which is the root cause described in the TSBs. (see via A professional-grade scanner or Ford-specific software like FORScan will display this two-part code. Basic OBD-II readers may only show 'B1408'.)

Scan Tool Commands That Help

• FORScan / Ford IDS: RCM Module Reset / Clear Crash Data — After replacing the seat suspension mat and reconnecting all components, this function must be used to clear the hard fault from the RCM's memory. A simple 'Clear DTCs' command may not be sufficient to extinguish the airbag light if crash data is stored.
• Ford IDS: Programmable Module Installation (PMI) — This function is used if the entire RCM is being replaced. It allows the technician to download the vehicle's original 'As-Built' data from Ford's servers and program it into the new module, ensuring all vehicle-specific options are correctly configured.
• FORScan / Ford IDS: On-Demand Self Test — After a repair, running the RCM On-Demand Self Test will command the module to check all its inputs and outputs. This confirms that the new part is functioning correctly and that there are no other open circuits before putting the vehicle back into service.

Wiring & Ground Locations

• Restraints Control Module (RCM) — Located under the center console, directly beneath the handbrake assembly. Access requires removing the driver's seat and the handbrake mechanism.. This is the module that stores code B1408. While the fault is in the seat, all wiring from the seat mat assembly ultimately terminates at the RCM. A visual inspection of the RCM connectors is a final step if a new seat mat does not resolve the issue.
• Main Underseat Connector (Yellow) — The primary electrical connector for all SRS components in the driver's seat, located under the seat. It is a large, typically yellow, multi-pin connector.. This is the main junction between the body harness and the seat harness, which includes the wiring for the faulty suspension mat. Damage or a poor connection at this point can mimic the symptoms of a failed mat and should be inspected early in the diagnosis.
• Chassis Ground Point — There are several approved chassis ground points near the driver's seat base, often using one of the seat mounting bolts or a dedicated stud under the floor covering.. A poor ground for the RCM or seat sensors can cause erratic behavior and fault codes. While not a common cause for this specific TSB-related issue, verifying a clean, tight ground connection is part of a thorough diagnostic process.

OEM Part Supersession History

• TSB 21-2353 (Part numbers not specified, procedure only) → TSB 22-2263 — Updated service procedure.
  Heads up: Introduced part number LK4Z-61632A22-C for the repair kit.
• TSB 22-2263 → TSB 23-2235 — Updated the Title, Issue, Action, Service Procedure, and Part List.
  Heads up: Confirmed LK4Z-61632A22-C as the correct repair kit.
• TSB 23-2235 → TSB 24-2053 — Corrected the Parts List and updated a step in the Service Procedure.
• TSB 24-2394 → TSB 25-2182 — Latest update to the procedure and parts.

Model Year Variations Within This Range

• 2019 - 11-Feb-2021: Vehicles built on or before February 11, 2021, were equipped with the original seat suspension mat assembly that is prone to cracking and causing code B1408. Vehicles built after this date have the revised part from the factory and should not experience this specific TSB-related failure.