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Lamp Seat Belt Circuit Failure

Jump to the fix

Severity

High

Can I keep driving?

Avoid extended driving; visit a service soon.

First step

Prove the supply and the battery before you go anywhere near a control module.

  • BBody
  • 1Manufacturer-specific
  • 4Body
  • 28Sequence number

What does it mean?

B1428 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Ignition Switched Power Run/Crank Relay Circuit .

Symptoms

  • Intermittent no crank or no start, sometimes curing itself after several key cycles
  • Engine cuts out while driving and restarts a moment later
  • Dashboard warning lights flicker or the cluster resets as the key is turned
  • Several unrelated modules set communication or supply codes at the same time
  • Accessories drop out together, or the battery goes flat overnight if the relay sticks closed

Likely causes

  • Faulty run/crank relay in the fuse box with burnt or sticking contacts
  • Blown fuse or a relay socket whose terminals have overheated and lost tension
  • Open circuit or high resistance in the run/crank feed between the fuse box and the module
  • Worn ignition switch contacts that no longer pass a clean run and crank signal
  • Corroded or loose fuse box connector, common where water has entered an under bonnet box
  • Poor module ground making the supply appear low even when it is present
  • Weak battery or bad main cable connections dropping voltage heavily during cranking
  • Internal fault in the module that drives or monitors the relay

How to fix it

  1. Load test the battery and check the charging voltage, since a weak battery is a very common trigger for this code
  2. Clean and tighten the battery terminals, the main ground straps and the engine to body ground
  3. Locate the run/crank relay, swap it with an identical relay elsewhere in the box and see whether the fault moves
  4. Inspect the relay socket and fuse box terminals for heat damage, discolouration and slack contacts
  5. Voltage drop test the run/crank feed with the ignition on and again while cranking, comparing the reading at the module with the reading at the fuse box
  6. Check the ignition switch output for a steady signal through the whole key sweep
  7. Repair the wiring, replace the relay or the switch as proven, then clear the codes in every affected module and confirm the fault does not return over several start cycles

Codes From the Same System

All Fault Codes

Related Similar Codes

This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.