What Does B1721 Mean?
DTC B1721 indicates the Body Control Module (BCM) has detected an electrical fault in the driver's seat rearward position switch circuit. This code sets when the BCM identifies an open circuit, short circuit, or abnormal voltage/resistance in the wiring or switch that controls the rearward movement of the power driver's seat. The BCM continuously monitors this circuit and triggers the code when electrical parameters fall outside expected ranges.
Common Causes
35%
Faulty or worn driver seat rearward position switch with internal contact failure
30%
Damaged wiring harness or connector pins under the driver seat due to seat movement, moisture intrusion, or physical damage
20%
Corroded or loose electrical connector at seat switch or BCM interface causing intermittent circuit failure
10%
Short circuit to power or ground in seat motor circuit affecting switch signal feedback
5%
Failed Body Control Module with internal circuit fault in seat control module
Diagnostic Steps
1
Step 1: Perform visual inspection under the driver seat, checking for damaged wiring, pinched harnesses from seat rails, moisture contamination, and corrosion at all connectors. Move the seat forward/rearward while inspecting for wire chafing or movement-related damage.
2
Step 2: With ignition off, disconnect the seat rearward switch connector and inspect terminals for corrosion, bent pins, or moisture. Clean terminals with electrical contact cleaner if contamination is present.
3
Step 3: Using a digital multimeter, test the rearward switch continuity by measuring resistance across switch terminals while manually activating the switch (typically should show 0-5 ohms closed, infinite ohms open). Compare readings to manufacturer specifications if available.
4
Step 4: Check for voltage supply at the switch connector with ignition on (typically 5V or 12V reference voltage). If no voltage present, trace wiring back toward BCM checking for opens or shorts using continuity tests with power disconnected.
5
Step 5: If switch and wiring test good, perform BCM connector inspection and voltage/ground verification at the BCM side of the circuit. Check BCM ground integrity with voltage drop test (should be less than 0.1V).
6
Step 6: After repairs, clear codes, cycle the seat rearward switch multiple times through full range of motion, and verify code does not return. Test seat operation in all directions to confirm proper function.
Estimated Repair Cost
$100 - $450
Parts + labor, varies by vehicle and location
DTC B1721 indicates the Body Control Module (BCM) has detected an electrical fault in the driver's seat rearward position switch circuit. This code sets when the BCM identifies an open circuit, short circuit, or abnormal voltage/resistance in the wiring or switch that controls the rearward movement ...
The most common cause of B1721 (Seat Driver Rearward Switch Circuit Failure) is: Faulty or worn driver seat rearward position switch with internal contact failure
Typical repair costs for B1721 range from $100 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive with this code as it only affects power seat adjustment functionality. The seat position may not adjust rearward electrically, but manual operation or other seat functions may still work. Repair at convenience, though extended delay may cause ergonomic discomfort for different drivers.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1721 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System (Power Seat Control)
Difficulty
Type
Manufacturer
Recommended Tools
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