B1985 — Seat Switch Lumbar Deflate Circuit Failure #

Note: The description for B1985 may vary depending on the vehicle manufacturer (OEM). Always consult your vehicle’s service manual for the most accurate wording and diagnostic procedures.

• Seat Switch Lumbar Deflate Circuit Malfunction (Ford, Lincoln, Mercury)
• Lumbar Support Switch Circuit Deflate Fault (General Motors/Chevrolet)
• Seat Adjuster Lumbar Deflate Signal Error (Chrysler, Dodge, Jeep)

Code summary for B1985 #

B1985 indicates a malfunction in the electrical circuit responsible for the lumbar support deflate function of a vehicle seat. This code is triggered when the Body Control Module (BCM) or Seat Control Module detects an abnormal voltage, resistance, or signal loss in the wiring or switch that controls the lumbar support’s deflation feature. In plain terms, the system can’t properly release air or mechanical pressure from the lumbar support, usually due to a switch, wiring, or actuator issue. While this doesn’t affect the core drivability of your vehicle, it does impact seat comfort and could indicate deeper wiring problems, especially if other seat controls are acting up. Prompt attention is recommended to prevent further electrical complications and restore full seat functionality.

Common symptoms for DTC B1985 #

When B1985 is stored, you may notice changes in how your seat feels or responds. The most obvious sign is the failure of the lumbar support to properly deflate, which can make long drives uncomfortable. Sometimes, the seat switch may feel unresponsive or intermittent. Rarely, you might see a seat-related warning light on your dashboard.

• Lumbar support remains inflated or does not release pressure
• Lumbar adjustment switch does not respond when pressed to deflate
• Noticeable discomfort due to fixed or overly firm lumbar support
• Other seat adjustments may work normally
• Possible seat or airbag warning light (varies by OEM)

Most probable causes for B1985 #

Not all causes are equally likely. Based on field experience, some issues occur more frequently than others. Here are the most common culprits, ranked by frequency:

1. Faulty lumbar support deflate switch — The physical button or rocker that tells the system to release lumbar support may be worn or have internal contact issues.
2. Open or shorted wiring in the lumbar deflate circuit — Broken, pinched, or corroded wires between the switch and seat module are a frequent root cause.
3. Defective seat control module — The control unit that receives the signal may have internal faults.
4. Failed lumbar actuator or air pump (if equipped) — On vehicles using pneumatic lumbar systems, the pump or deflate valve can fail electrically.
5. Poor connector contact or corrosion at seat connectors — Water intrusion or age can degrade contacts.

Step-by-step diagnosis for B1985 #

Accurate diagnosis prevents unnecessary part replacement. Here’s how a professional technician would typically approach B1985:

1. Use a scan tool to confirm B1985 and check for other related seat or body control codes.
2. Visually inspect the lumbar support switch and its surrounding trim for obvious damage or spilled liquids.
3. Disconnect the seat wiring harness; inspect all connectors for bent pins, corrosion, or loose contacts.
4. With the battery disconnected, check continuity and resistance of the lumbar deflate circuit using a digital multimeter.
5. If wiring is intact, test the lumbar deflate switch for correct operation and resistance values (per OEM specs).
6. Command the lumbar deflate function with a scan tool (if possible) and observe seat module response.
7. If all above components test good, suspect a faulty seat control module or actuator and test per OEM procedure.

Possible repairs for B1985 #

Once the root cause is pinpointed, the following repairs may be carried out to clear B1985 and restore lumbar function:

• Replace the lumbar support deflate switch if it is unresponsive or tests out of spec.
• Repair or replace damaged wiring or connectors in the lumbar deflate circuit.
• Clean and secure all seat connectors to ensure proper electrical contact.
• Replace a defective seat control module (may require programming/reset by OEM procedures).
• Service or replace the lumbar actuator, valve, or air pump if found faulty (pneumatic seats only).

Is it safe to drive with code B1985? #

Yes, but with limitations. Code B1985 will not affect your vehicle’s core safety or drivability. However, you may find your seat less comfortable, especially on long journeys, and you will be unable to adjust lumbar support as intended. If other seat or airbag codes are present, further diagnosis is essential as those could have safety implications.

Vehicles most commonly affected by B1985 #

While B1985 can appear on any vehicle equipped with electrically adjustable lumbar support, it is most often seen in certain models from major manufacturers:

• Ford F-150, Explorer, Expedition, Taurus (2007–2018)
• Lincoln Navigator, MKZ (2008–2015)
• Chevrolet Silverado, Tahoe, Suburban (2010–2017)
• GMC Sierra, Yukon (2010–2017)
• Chrysler 300, Dodge Charger, Jeep Grand Cherokee (2011–2019)

Frequent mistakes & best practices for B1985 #

Avoiding common pitfalls will save you time and money. Here are mistakes seen in workshops, and the best ways to tackle this code:

• Assuming the lumbar switch is always to blame — wiring faults are just as common.
• Skipping connector inspection — many issues are due to loose or corroded pins.
• Replacing the entire seat module before testing the switch and wiring.
• Ignoring OEM diagnostic flowcharts and guessing at repairs.
• Neglecting to check for spilled liquids or physical damage around seat switches.

FAQ for code B1985 #

A few fast answers to the most common questions about this seat comfort code:

• Q: Can B1985 trigger airbag or safety system warnings?
  A: Not directly, but if multiple seat-related codes are present, check for airbag (SRS) faults as some seat modules share wiring or power.
• Q: Will clearing the code restore lumbar function?
  A: No. The code will return if the underlying issue (switch, wiring, module) is not repaired.
• Q: Can I replace just the lumbar switch myself?
  A: If you’re comfortable removing seat trim and using basic hand tools, yes — but always disconnect the battery and refer to your vehicle’s service manual to avoid airbag deployment risks.