B1978

Code

Other B — Body

Passenger's Front Seat Down Switch Circuit Short to Battery

Brand: Other

Type: B — Body

Views: UK: 23 EN: 28 RU: 16

AI status

Completed

ready

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Page language: EN

Causes

Damaged or pinched wiring contacting battery voltage
Shorted conductor inside the seat harness
Corroded or bent connector/pins creating a high-voltage feed
Failed seat position switch internally shorted to battery
Faulty seat control module or internal short
Aftermarket accessories or repairs altering wiring

Symptoms

Seat down function does not work or moves erratically
Seat may attempt to move without command or be stuck
Seat-related warning lamp or message on dash (manufacturer-dependent)
Stored B1978 fault code in body/seat control module
Intermittent seat operation or only works after connector manipulation

What to check

Scan and record freeze frame and all stored/related seat/body codes
Visually inspect seat wiring harness for damage, rubbing, or prior repairs
Inspect seat connector for corrosion, bent pins, or pushed-through terminals
Check fuses and related power feeds for the seat control module
Verify no aftermarket components (alarms, audio) are tied into seat circuits

Signal parameters

Normal: Switch input should be low (near 0 V) when switch not actuated and should change state when switch pressed; exact levels depend on manufacturer logic
Fault condition: Continuously reads battery voltage (~11–14 V) on the switch circuit when it should be low
Continuity: Closed switch to ground or module input may show low ohms; open switch shows high resistance/OL
Resistance: Intact switch circuit expected to show open/closed continuity consistent with switch position (typical low-ohm closed)

Diagnostic algorithm

Retrieve B1978 and any related codes. Note operating conditions and freeze-frame data.
With ignition on, backprobe the seat down switch signal wire at the seat connector or switch and observe voltage. Compare to expected: presence of battery voltage when switch is not actuated indicates short to battery.
Inspect the harness from the seat switch to the seat control module for rubbing, broken insulation, or pinched areas (focus on areas that pass through seat frame or door opening)
Disconnect the seat switch connector and measure the signal circuit voltage at the harness side. If battery voltage is still present with switch disconnected, the short is upstream of the switch (harness or power source).
Disconnect the seat control module connector and measure the signal wire. If voltage disappears, inspect module connector and module for internal short or bent pins.
Perform a wiggle test of the harness while monitoring voltage to reproduce intermittent faults.
If wiring appears intact, bench-test or replace the seat down switch and re-check. If replacement clears the fault, verify operation and clear codes.
If wiring is shorted to battery, isolate and repair the damaged wire (repair with proper crimp/splice or replace harness section). Protect routing to prevent reoccurrence.
After repair, clear codes and test seat functions through full range of motion and verify code does not return under normal conditions.
If fault persists after wiring and switch checks, consider seat control module diagnosis/repair or replacement per manufacturer procedure.

Likely causes

Chafed wire in harness contacting the vehicle's 12 V source (most common)
Connector terminal pushed into mating housing contacting 12 V terminal
Switch internal insulation breakdown causing battery feed to switch terminal
Water ingress in seat connector causing conductive path to battery
Previous repair used wrong wire routing and placed signal wire next to constant 12 V

Fault status

⚠️ Status

Passenger front seat down switch circuit is detecting a short to battery voltage. Inspect wiring, connectors, and switch for a 12 V short or replace faulty component.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours