B1977

Code

Other B — Body

Passenger's Front Seat Up Switch Circuit Short to Battery

Brand: Other

Type: B — Body

Views: UK: 21 EN: 56 RU: 19

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Page language: EN

Causes

Damaged or chafed wiring shorted to battery positive
Faulty passenger front seat up switch with internal short
Corroded or loose connector making unintended battery connection
Shorted splice or connector in same harness tied to constant 12V
Faulty seat control module or body control module input stage

Symptoms

Passenger front seat up function inoperative or intermittent
Related seat memory or power seat faults illuminated (seat warning/message)
Possible persistent diagnostic trouble code (B1977) in body/seat module
Blown related fuse in some cases if short is heavy

What to check

Verify battery voltage and system ground integrity before testing
Scan vehicle to confirm B1977 and read freeze frame / occurrence data
Visually inspect passenger seat wiring harness from switch to seat module for damage, pinch points, or contact with 12V sources
Inspect connectors at the seat switch and seat control module for corrosion, bent pins, or presence of moisture
Check related fuses and measure for signs of overheating

Signal parameters

Expected: With ignition ON and switch operated, switch circuit should change state between ~0 V (ground) and ~12 V (battery) depending on circuit design; consult vehicle wiring—some designs use pull-up to module and switch to ground
Measured symptom for this code: circuit reads persistent battery voltage (~12 V) regardless of switch actuation
Typical continuity: closed switch ≈0–5 Ω; open switch >>1 kΩ (or infinite) depending on design
If the circuit is shorted to battery, resistance to battery positive will be very low (near 0 Ω)

Diagnostic algorithm

Retrieve freeze frame and confirm MIL history. Clear code and attempt to reproduce to ensure it's current.
Disconnect battery negative terminal if required by manufacturer safety procedures before working on seat harness.
Visually inspect harness along full route under the seat and rearward for chafes, pinches, or contact with 12V wiring (seat heater, blower, airbag squib). Repair obvious damage.
With harness accessible, reconnect battery and backprobe the seat up switch signal wire at the connector. Measure voltage with ignition ON and with switch operated. Note whether voltage stays at battery level regardless of switch position.
If the circuit reads constant battery voltage, unplug the switch and measure voltage at the switch connector pin. If battery voltage is still present with switch unplugged, a short to battery exists upstream (wiring or module).
If voltage disappears when switch unplugged, bench-test the switch: measure resistance between switch terminals when actuated. Replace switch if it remains conducting to battery or shows incorrect resistance.
If short is upstream, trace wiring toward the seat module. Disconnect intermediate connectors and retest to isolate section causing short. Repair or replace damaged wiring or connectors.
If wiring and switch check good, test input pin at the seat control or body control module for internal short. Check for diagnostic procedures from manufacturer to test module. Replace module only after wiring and switch faults are ruled out.
After repairs, clear codes and perform function test and road test if applicable to confirm fault does not return.