P0606, P0605 and other ECU internal fault codes (P0600–P0606)
The P060x codes are set when the engine ECU (or PCM) detects a fault inside itself. They don't always mean the ECU is scrap — but they are a reason to check power, earth and wiring carefully before spending money.
What the codes mean
- P0600 — serial communication link fault.
- P0601 — internal control module memory checksum error.
- P0602 — control module programming error.
- P0603 — internal control module keep-alive memory (KAM) error.
- P0604 — internal control module RAM error.
- P0605 — internal control module ROM error.
- P0606 — control module processor fault.
Check these first
- Battery condition and charging voltage — a weak battery or failing alternator can set internal codes.
- ECU power feeds, fuses and main relay, and the ECU earths (clean and tight).
- Water in the ECU connector or signs of corrosion.
- Whether the fault appeared after a jump start, welding, a remap or a failed software update.
- Manufacturer technical bulletins — some ECUs have a software update for a known internal-fault code.
When the ECU really is faulty
- If the ECU has a board fault (for example a failed power supply or driver stage), it can often be repaired at component level, keeping your original data.
- If the board can't be repaired, the usual answer is a matching second-hand ECU with your original's data transferred into it (cloning), so it works with your keys and car without dealer programming in most cases.
- Send us your part number and a label photo and we'll tell you which applies.
Questions
Can I just clear P0606 and carry on?
If it comes back, the underlying cause is still there. Check power and earths first; a persistent P0606 usually needs the ECU inspected.
Will a used ECU fix P0606?
Only once your original's data is transferred into it — otherwise the immobiliser won't let it start the engine.
Need it checked?
Send your part number and a label photo — we'll tell you whether it's a repair or a clone, and the price, before you post.
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General guidance only — always diagnose the vehicle properly. Fault code meanings are the generic (SAE) definitions; manufacturers may add their own.