What Does B1985 Mean?
B1985 indicates the Body Control Module (BCM) or Seat Control Module has detected a malfunction in the lumbar deflate circuit of the power seat adjustment system. The module commands the lumbar bladder to deflate but detects an abnormal voltage, current draw, or lack of expected feedback from the deflate valve or circuit. This prevents proper lumbar support adjustment and indicates an electrical fault in the deflate control pathway.
Common Causes
40%
Faulty lumbar deflate solenoid valve or actuator motor within the seat assembly
30%
Damaged wiring harness, corroded connector pins, or broken wires between seat control module and lumbar deflate valve
20%
Failed seat control module or integrated seat switch assembly with internal circuit damage
10%
Blown fuse or open circuit in power supply to lumbar system components
Diagnostic Steps
1
Step 1: Perform visual inspection of the driver or passenger seat wiring harness beneath the seat for pinched wires, damaged insulation, or corroded connectors where the seat moves on its tracks
2
Step 2: With ignition on, use a multimeter to check for battery voltage at the lumbar deflate valve connector and verify ground circuit continuity (should be less than 1 ohm to chassis ground)
3
Step 3: Disconnect the lumbar deflate solenoid connector and measure resistance across the solenoid terminals (typical range 10-50 ohms); infinite resistance indicates open coil, near-zero indicates short circuit
4
Step 4: Using scan tool bidirectional controls, command the lumbar deflate function while monitoring current draw with a multimeter (should be 0.5-2 amps typically); no current or excessive current confirms component failure
5
Step 5: If wiring and solenoid test good, substitute or reflash the seat control module if available, then clear codes and retest lumbar deflate function through all adjustment ranges
6
Step 6: After repairs, cycle the lumbar support through full inflate/deflate sequence at least 5 times and verify no codes return and proper operation is restored
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
B1985 indicates the Body Control Module (BCM) or Seat Control Module has detected a malfunction in the lumbar deflate circuit of the power seat adjustment system. The module commands the lumbar bladder to deflate but detects an abnormal voltage, current draw, or lack of expected feedback from the de...
The most common cause of B1985 (Seat Switch Lumbar Deflate Circuit Failure) is: Faulty lumbar deflate solenoid valve or actuator motor within the seat assembly
Typical repair costs for B1985 range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This is safe to continue driving as it only affects comfort features and does not impact vehicle operation, braking, or steering. Repair can be scheduled at convenience though prolonged discomfort may affect driver alertness on long trips.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1985 to identify the root cause.
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Quick Info
Category
Body
System
Power Seat Adjustment System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
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