DTC P0604: Pcm Random Access Memory Error

Fig 1: DTC P0604 Detection Condition & Possible Causes Chart

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Diagnostic Procedure 

Fig 2: DTC P0604 Diagnostic Procedure Chart (Step 1-2)

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Fig 3: DTC P0604 Diagnostic Procedure Chart (Step 3-4)

Courtesy of MAZDA MOTORS CORP.