B1979 — Passenger Seat Rearward Switch Circuit Short to Battery #

The description for code B1979 may vary depending on the vehicle manufacturer (OEM). Below is a list of known variations for this code’s label:

• Passenger Seat Rearward Switch Circuit Short to Battery (Ford, Lincoln, Mercury)
• Front Passenger Seat Backward Movement Switch – Circuit Short to Battery (Mazda)
• Seat Adjust Rearward Switch Circuit Short to B+ (General Motors)

Summary of Code B1979 #

The B1979 code indicates that the passenger seat rearward switch circuit has experienced a short to the vehicle’s battery voltage (“B+”). In practical terms, the circuit responsible for moving the passenger seat backward is receiving constant voltage, often due to a wiring or switch fault. This is a Body Control Module (BCM)-related code, meaning it originates from the part of the vehicle electronics responsible for interior features and comfort functions. If this code is present, seat adjustment may be erratic or non-functional, potentially affecting passenger comfort and safety. Prompt attention is advisable to prevent further electrical issues or discomfort.

Common Symptoms for Code B1979 #

When your vehicle’s system stores the B1979 code, you’ll often notice some obvious and some subtle changes in the way the passenger seat operates. The symptoms are usually limited to the seat’s rearward adjustment, but sometimes, related features may also act up. Here’s what you might observe:

• Passenger seat won’t move backward when pressing the adjustment switch
• Seat may move backward by itself or unexpectedly
• Switch feels hot to the touch or is unresponsive
• Possible clicking or buzzing sound under the seat
• Other seat adjustment directions may still work normally
• “Seat Adjustment Inactive” message or similar on the dashboard

Probable Causes for Code B1979 #

Several issues can lead to a B1979 code, but some are more frequent than others. Typically, the root cause involves an electrical short, often where wiring is routed around moving seat parts. Here’s what most commonly causes this code, from most to least likely:

1. Damaged wiring harness: Chafed, pinched, or cut wires under the passenger seat
2. Faulty rearward seat switch: Internal short within the adjustment switch
3. Corroded or loose seat connectors: Poor contacts causing unintended voltage connections
4. Faulty seat control module: Internal circuit failure (less common)
5. Improper aftermarket installation: Add-ons or repairs interfering with seat wiring

Step-by-Step Diagnostic for Code B1979 #

A thorough diagnosis will save you from chasing ghosts—and unnecessary part replacements. Always start with the simplest checks and work your way up. Here’s a proven process:

• 1. Visual Inspection: Slide the passenger seat fully forward and inspect the wiring and connectors underneath for damage, pinching, or corrosion.
• 2. Check Fuse and Power Supply: Verify the seat adjustment circuit fuse and ensure the B+ supply is correct (no blown fuse, proper voltage).
• 3. Test Switch Function: Using a multimeter, test the rearward switch for continuity and check for a short to battery voltage with the ignition on and off.
• 4. Inspect Connectors: Unplug the seat switch and seat module connectors. Look for bent pins, corrosion, or signs of arcing.
• 5. Wiggle Test: With the system powered, gently move the harness and connectors to see if the code resets or the seat reacts unexpectedly.
• 6. Scan Tool Verification: Use an OEM-compatible scan tool to clear the code. See if it returns after performing switch operations.
• 7. Module Check: If all else checks out, use wiring diagrams to test the seat control module for internal shorts or improper output.

Possible Repairs for Code B1979 #

Once you’ve pinpointed the cause, the following repairs often resolve the B1979 code. Always address the root issue, not just the symptom, to ensure a lasting fix.

• Repair or replace damaged wiring: Patch, re-route, or replace any frayed, pinched, or cut wires found during inspection.
• Replace faulty seat switch: If the switch is shorted internally, installing a new OEM switch is recommended.
• Clean or replace corroded connectors: Use electrical contact cleaner, and if needed, replace damaged connectors.
• Replace seat control module: If diagnosed as faulty, install a new or remanufactured module, followed by reprogramming if required.
• Correct aftermarket wiring errors: Remove or properly integrate any non-OEM components interfering with the seat circuit.

Is It Safe to Drive with Code B1979? #

Limited – Caution Advised. While B1979 does not typically pose an immediate safety risk or cause drivability issues, it can affect passenger comfort and, in rare cases, passenger safety in the event of an accident (such as inability to adjust the seat for proper airbag alignment). Additionally, electrical shorts can sometimes lead to blown fuses or, in extreme cases, an increased risk of overheating or fire if ignored. It’s best to address this code promptly and avoid using the affected seat adjustment until repaired.

Vehicles Most Commonly Affected by Code B1979 #

While B1979 is a generic OBD-II/EOBD code, it is more frequently reported in vehicles where power seats and advanced interior electronics are standard. The following brands and models are often associated with this code:

• Ford (Fusion, Taurus, Edge, Explorer, Expedition, F-150)
• Lincoln (MKZ, MKS, Navigator)
• Mercury (Milan, Sable)
• Mazda (6, CX-9)
• General Motors (Chevrolet Malibu, Buick LaCrosse, GMC Acadia)

Common Mistakes and Best Practices for Code B1979 #

It’s easy to misdiagnose this code if you rush or overlook wiring issues. Here are pitfalls to avoid and best practices to follow:

• Don’t replace the seat control module first: Wiring and switches are far more common culprits.
• Always inspect wiring under full seat movement: Damage often hides in hard-to-see areas or occurs only when the seat is moved fully forward/back.
• Don’t ignore aftermarket modifications: Alarm, audio, or seat heater installs often disturb OEM wiring.
• Document connector conditions and pin-outs: Take notes or photos—this helps track down intermittent faults.
• Use OEM parts where possible: Aftermarket switches or connectors may not match original specs and create recurring problems.

Express FAQ for Code B1979 #

Diagnosing and fixing a seat circuit code can feel like searching for a needle in a haystack. Here are two common questions and answers to help you cut through the confusion:

• Q: Can I manually move the seat if the switch is faulty?
  A: In most vehicles, power seats can’t be adjusted manually without special tools or procedures. Forcing the seat may cause further damage. Always repair the circuit first.
• Q: Will disconnecting the battery clear the B1979 code?
  A: Disconnecting the battery may temporarily clear the code, but if the underlying issue isn’t fixed, the code will return once the system detects the fault again.