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DTC codes / P06xx · Computer and output circuits / P0606

P0606PCM Processor Fault

P0606 is a generic powertrain code indicating that the Powertrain Control Module (PCM) has detected an internal processor fault, meaning the computer's central processing unit or its supporting circuitry has failed a self-test. The PCM monitors its own processor, memory, and internal communication buses, and when the processor fails to execute instructions correctly or reports an internal error, it sets this code and typically illuminates the check engine light.

SystemPowertrain
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Check engine light illuminated, often with no other noticeable symptoms
  • Engine may stall or fail to start intermittently
  • Rough running or misfire-like behavior due to corrupted fuel and spark control
  • Transmission may shift erratically or enter limp mode
  • Other unrelated trouble codes may be stored simultaneously
  • Reduced engine performance or throttle response

Common causes, most likely first

  1. Internal failure of the PCM processor or its supporting circuitry
  2. Low or unstable battery voltage causing the PCM to misreport a processor fault
  3. Corroded or loose grounds at the PCM or engine block
  4. Damaged or chafed wiring in the PCM harness, especially near the processor pins
  5. Water intrusion into the PCM connector or case
  6. Aftermarket electronic devices or poor previous repairs interfering with PCM power or ground
  7. Failed PCM power relay or blown fuse causing intermittent voltage to the processor

How to diagnose and fix it

  1. Perform a thorough visual inspection of the PCM connectors, harness, and grounds for corrosion, water, or damage
  2. Test battery voltage and charging system output; load-test the battery and check for voltage drops on PCM power and ground circuits
  3. Clear the code and verify whether it returns immediately or only under specific conditions such as vibration or temperature extremes
  4. Check for technical service bulletins (TSBs) or software updates for the PCM that address false P0606 setting
  5. If the code persists after electrical checks, perform a pinpoint test for the PCM processor circuit as outlined in the factory service manual
  6. Replace and reprogram the PCM only after all power, ground, and wiring faults have been ruled out
  7. After repair, clear codes and perform a road test to confirm the processor self-test passes and no codes return

Before you replace the PCM for P0606

  • A weak or failing battery is one of the most common causes of a false P0606 because the PCM's processor self-test can fail during cranking if voltage drops too low.
  • Corroded ground straps between the engine and chassis often set this code without any other symptoms, and cleaning them frequently resolves the issue.
  • Aftermarket remote starters, alarms, or poor wiring repairs tapping into the PCM harness can introduce voltage spikes that the processor interprets as an internal fault.
  • P0606 does not always mean the PCM is permanently damaged; it can be a one-time event caused by a transient voltage spike, so clearing and rechecking is a valid first step.
  • Some vehicles set P0606 when the PCM detects an internal communication error with another module, so checking for related codes in the transmission control module or body control module is worthwhile.

Can I keep driving with P0606?

Because a failing PCM processor can cause stalling, loss of power, or erratic transmission behavior without warning, you should avoid driving the vehicle until the fault is diagnosed. If the engine runs normally and the code was a one-time event, a cautious short trip to a repair shop may be acceptable, but towing is safer if any drivability symptoms are present.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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