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1996 TOYOTA 4RUNNER
3.0L V6•4WD•AUTOMATIC•gas
5 active safety recalls on this vehicle — view recalls
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Repairs0Labor1026Torque6708Fluid18DTC1806Battery2Maintenance0Recalls5
P0421moderate severityPowertrain

Warm Up Catalyst Efficiency Below Threshold Bank 1

on 1996 Toyota 4Runner 3.0L V6 · 4WD

What this code means

The Bank 1 warm-up catalytic converter is not efficient during the warm-up period.

Symptoms

  • Check Engine Light
  • Failed emissions test

Common causes

  • Worn catalyst
  • Engine running rich during warm-up
  • O2 sensor issue
  • Exhaust leak

Diagnostic steps

  1. Monitor catalyst temps during warm-up
  2. Compare O2 sensor signals
  3. Check for exhaust leaks

Repair notes

Replace warm-up catalyst if confirmed failed.

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