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DTC 420: ECC Control Module Memory Circuits, Internal Fault &/Or DTC 421: ECC Control Module PROM, Internal Fault

  1. Turn ignition on. Wait 10 seconds so ECC control module can run diagnostics. Using scan tool, read off DTC counters. If counter value is greater than zero, fault is not longer present. If counter value is less than zero, go to next step.
  2. Ensure ignition is on. Use scan tool programming function to read out data from ECC control module and note values. Program new ECC control module with these values. See PROGRAMMING ECC CONTROL MODULE  .
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