P0606

P0606 is set when the PCM's internal processor self-test fails — the main CPU itself is reporting a fault, either by detecting a watchdog timeout, an arithmetic-logic-unit error, or a failed cross-check between the primary and monitoring processors that most modern PCMs run side-by-side. This is the most definitive 'PCM is dead' code in the OBD-II set. Cheapest-first verification still applies: battery at 12.4V+ at rest, no more than 0.5V drop under accessory load, all grounds under 0.1V drop, no water intrusion at the PCM, no aftermarket back-feed on sensor reference wires. Attempt a J2534 reflash with a regulated power supply held at 13.5V minimum; on rare occasions a corrupted calibration causes the monitoring processor to flag the main CPU as faulty, and a clean flash recovers the module. If the PCM will not communicate, intermittently drops off the bus, sets U-codes in other modules, or returns P0606 immediately after a successful flash, replace it. The expensive misdiagnosis is chasing sensor codes, ignition-system faults, or transmission codes that appear alongside P0606 — those downstream codes are symptoms of a confused processor, not independent faults, and replacing those parts will not fix the underlying P0606.

Vehicle-specific patterns: 2004-2007 Cadillac CTS, SRX, and STS with the E40 PCM are a well-known P0606 pattern, often with random sensor codes and harsh shifts, requiring PCM replacement and SPS programming per GM bulletin 06-06-04-039. 2003-2008 Dodge Ram and Durango with the early NGC module commonly set P0606 from heat-induced processor fatigue, addressed only by module replacement and wiTECH reprogramming. 2004-2010 Ford F-150 and Expedition with the Copperhead PCM throw P0606 alongside torque-converter shudder codes; Ford TSB 09-24-7 confirms PCM replacement as the fix when ground and voltage checks pass. 2005-2009 Subaru Legacy, Outback, and Forester with the Hitachi ECM show P0606 from internal microprocessor failure, requiring dealer programming and immobilizer relink. Estimated repair: $700 to $2,200.