What does OBD code P0606 mean?
P0606 indicates an internal fault in the engine control module (ECM) or powertrain control module (PCM) — the main engine computer. This is different from most codes where the ECU detects a fault in another component; here, the ECU is reporting a fault within itself. Symptoms can include engine management light, limp mode, poor performance, or in some cases the car refusing to start. Before replacing the ECU (which is expensive), a specialist should verify the code is genuine and rule out wiring issues.
Likely causes
Internal ECM/PCM processor fault
The control module hardware has failed internally — requires replacement or specialist remanufacture
ECM power supply or earth fault
Poor voltage supply or a bad earth to the ECU can cause it to report internal errors — check battery and earths first
Software or calibration fault
An interrupted ECU update or corrupt calibration file can trigger P0606 — re-flash may resolve it
Water or corrosion damage to ECU
ECUs can be damaged by water ingress, often from leaks in the bulkhead or footwell
Battery voltage spike
A faulty alternator or jump-start gone wrong can damage the ECU
Repairs you may need
Typical cost range: £150–£1200 — ECU supply/earth check: £60–120. ECU remap/re-flash: £150–300. ECU remanufacture: £200–500. ECU replacement (new): £400–1,200+.
Got a quote for this repair?
Check every line in 60 seconds — labour hours, parts prices, and regional rates.
Check My Quote Free