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Home / DTC / B1878 — Pre-tensioner of the left seat belt - short circuit to the battery

B1878 — Pre-tensioner of the left seat belt - short circuit to the battery

Detailed page for trouble code B1878.

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B1878

LAND ROVER B — Body

Pre-tensioner of the left seat belt - short circuit to the battery

Brand: LAND ROVER
Type: B — Body
Views: UK: 6 EN: 9 RU: 4
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Page language: EN

Causes

  • Positive voltage present on the pretensioner circuit (short to battery)
  • Damaged or chafed wiring harness contacting a battery feed or ignition feed
  • Corroded or damaged pretensioner connector or terminals
  • Internal short in the pretensioner (squib) assembly
  • Faulty airbag/SRS control module or driver output shorted

Symptoms

  • SRS / airbag warning lamp illuminated
  • Seat belt pretensioner disabled (no activation during a crash)
  • Unable to clear the DTC until fault cured
  • Possible other SRS-related DTCs or loss of related restraint functions

What to check

  • Record freeze-frame and all stored SRS DTCs with a compatible scan tool
  • Visually inspect left seat wiring, connector and routing for damage, pinched areas, corrosion or aftermarket splices
  • Inspect and verify SRS fuses and any seat-belt pretensioner fuses/relays
  • With ignition OFF and battery isolated per manufacturer procedure, measure continuity/resistance of pretensioner squib
  • Measure voltage at the pretensioner connector with ignition ON and key OFF (per wiring diagram) to identify presence of battery voltage
  • Check for signs of prior collision repair or replaced seat/pretensioner

Signal parameters

  • Normal pretensioner resistance (typical squib): approx. 0.8–3.5 Ω (manufacturer-specific — consult data)
  • Open circuit: very high resistance / OL
  • Short to battery: connector shows ~12 V (or battery voltage) on pretensioner positive terminal when it should be inactive
  • Short to ground: near 0 V on the pretensioner positive terminal when expected to be ~12 V or controlled by SRS module

Diagnostic algorithm

  1. Safety first: follow manufacturer SRS disable procedures before touching connectors or performing resistance checks (disconnect battery and wait specified time).
  2. Connect a diagnostic scan tool, retrieve and document all SRS DTCs and freeze-frame data.
  3. Perform a careful visual inspection of the left seat harness, airbag/pretensioner connector, seat frame and under-seat area for chafing, pinched wires, corrosion or aftermarket splices; repair any visible damage.
  4. Verify SRS/pretensioner fuses and connectors intact; repair or replace blown fuses only after locating cause.
  5. With SRS disabled per procedure, disconnect the pretensioner connector and measure resistance across the squib terminals; compare to manufacturer spec. A very low resistance consistent with a short or a resistance inconsistent with spec suggests internal pretensioner failure.
  6. With harness disconnected from the pretensioner, check for battery voltage on the harness side (ignition OFF and ON as required by wiring diagram). Presence of battery voltage on the harness indicates a short to a battery feed—trace wiring back to find the point of contact.
  7. If no external short is found and harness wiring is good, consider replacement of pretensioner and retest resistance and voltage.
  8. If replacement pretensioner does not clear the code, inspect and test SRS control module outputs and associated wiring harnesses; consult wiring diagrams and component test procedures.
  9. After repairs, clear DTCs with scan tool and perform a full SRS system check to confirm fault is resolved and no other codes are present.

Likely causes

  • Chafed wiring where harness rubs on body or seat frame and contacts a live feed
  • Corroded/contaminated connector allowing battery voltage onto squib circuit
  • Failed pretensioner with internal short to battery
  • Incorrect/poor repair or aftermarket seat wiring creating a direct feed

Fault status

⚠️ Status
Left seat belt pre-tensioner circuit — short to battery detected. SRS fault stored (B1878).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-2 hours

Similar codes

B1877 B1879 B1880
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