B1878

Code

Other B — Body

Seatbelt Driver Pretensioner Circuit Short to Battery

Brand: Other

Type: B — Body

Views: UK: 29 EN: 38 RU: 32

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Page language: EN

Causes

Damaged wiring harness (chafing, pinched, melted) to driver pretensioner
Corroded or damaged connector at pretensioner or SRS control module
Faulty driver seatbelt pretensioner (squib) with internal short
Shorted terminals inside steering column/clock spring (if pretensioner pass-through is routed there)
Faulty SRS/airbag control module or internal driver circuit fault
Aftermarket accessories or previous repairs that modified/shorted the circuit

Symptoms

SRS/airbag warning lamp illuminated on dash
Possible stored SRS codes related to driver pretensioner circuit
Seatbelt pretensioner may not function when deployed
Some vehicles may log multiple related SRS faults (module comms or other squib circuits)

What to check

Read and record all stored SRS codes with a capable scan tool and note freeze frame data
Visually inspect wiring and connectors at driver seat pretensioner, seat base, B‑pillar, and SRS module for damage, corrosion, or melted insulation
Check for signs of recent repairs or aftermarket wiring near seat wiring harness
Confirm battery voltage and overall vehicle electrical health (low or spiking voltage can complicate diagnosis)
Do not attempt resistance measurements on an airbag squib with the system armed — follow safety procedures before probing

Signal parameters

Normal squib circuit: open or high resistance when intact (typically hundreds to thousands of ohms depending on design)
Short to battery: circuit voltage near battery positive (~11–14 V) at the pretensioner connector when measured relative to vehicle ground (with system powered)
Short to ground: circuit voltage near 0 V (not this code)
Expected control module squib line voltage pulses only during deployment command (do not trigger)

Diagnostic algorithm

Safety first: follow manufacturer SRS safety procedures. Disable vehicle battery and wait the manufacturer‑specified time for SRS capacitors to discharge before touching SRS components or connectors.
With ignition OFF and SRS disabled per manufacturer instructions, visually inspect the pretensioner connector, wiring harness, and routing for damage, chafing, heat/melt marks, or corrosion.
Reconnect battery and use a scan tool to monitor live data and confirm B1878 is active. Record any additional SRS codes.
With proper safety measures and following manufacturer guidance, measure voltage at the pretensioner connector (backprobing) while ignition ON (system armed). A short to battery will show battery voltage present on the squib feed when it should normally be low/open.
If battery voltage is present, isolate the short by disconnecting sections of the harness: unplug pretensioner connector and check if voltage remains on the harness side. If voltage disappears when connector is unplugged, suspect pretensioner short. If voltage remains, trace wiring toward the module to find pin/connector/short.
Measure continuity/resistance between squib positive and battery positive/other circuits only after SRS disabled and per manufacturer instructions. Low resistance to battery positive indicates short.
Inspect connectors at the SRS control module and steering column/clock spring (if applicable). Repair or replace damaged wiring or connectors; replace pretensioner if internal short is confirmed.
After repairs, clear codes with a scan tool, perform SRS system checks per manufacturer procedures, and verify fault does not return. If codes persist after wiring/pretensioner replacements, consider SRS control module evaluation by a qualified specialist.

Likely causes

Damaged or chafed wiring near the seat or B‑pillar causing contact with battery positive
Corroded/loose connector at the pretensioner making intermittent short
Failed pretensioner squib with internal short to battery
Clock spring or steering harness damage (if circuit routes through steering)