P0606: The engine computer processor has a fault
PCM Processor Fault
The engine computer reported an internal processor fault. Get it checked as soon as you can. If it will not start, stalls, or engine or transmission control seems wrong, have it towed.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0606 means the PCM detected a fault in its own internal processor during a self-diagnostic check. The processor is the calculating core of the engine computer. Unlike P0601, which is a memory error, P0606 is a processing fault. This often means the PCM itself has failed and needs replacement or reprogramming. However, low battery voltage, ground faults, and certain wiring issues can force false processor faults by starving the PCM of the stable power it needs to run correctly. Always verify the electrical system before replacing the PCM.
Common causes
- Internal PCM processor failureThe processing chip inside the PCM has failed. Requires replacement.
- Unstable or low supply voltage to the PCMPCMs require stable voltage. A failing battery or loose ground can cause processor faults.
- Bad PCM ground connectionA corroded or loose PCM ground strap is a common trigger, especially on older vehicles.
- Software corruption requiring reflashOn some models, a manufacturer reflash resolves the fault without hardware replacement.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- PCM reflash or reprogramming
- PCM replacement and programming
Symptoms
- Check engine light on
- Multiple systems may malfunction simultaneously
- Erratic engine behavior
- Possible no-start
- Other codes stored alongside P0606
What to do next
Check all PCM power and ground connections first. Inspect the main PCM ground strap where it attaches to the chassis or engine block for corrosion. Verify battery voltage is within spec. If the electrical system is sound, bring the vehicle to a dealer or independent shop with factory diagnostic tools. Check if a technical service bulletin exists for P0606 on your model before authorizing PCM replacement.
Lewis saves every code from the scan to your history, which helps establish whether P0606 appeared alongside other faults or on its own. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Is P0606 always a PCM failure?
- Not always. Check battery voltage, ground connections, and TSBs for your model before replacing the PCM. Some cases are electrical, not hardware.
- How much does a replacement PCM cost?
- It depends heavily on the vehicle. The module itself is the big part, and it usually needs programming to your car on top. Ask for a written quote that names the module, the programming and the labor, and confirm the diagnosis before you pay for it.
- Can I buy a used PCM?
- Sometimes, but used PCMs must be programmed to your specific VIN. Not all used modules can be reprogrammed. Confirm with your shop before buying one.
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