Code P0606: ECU (ECM/PCM) internal processor fault

Original definition (SAE J2012): Control Module Processor (ECM/PCM Processor Fault)^{[1][2][3][4][5][6]}

1. 1Internal fault of the ECU itself: damaged module, internal circuits or memory. It is the cause the sources cite first.^{[1][2][3][4][5][6]}
2. 2Corrupted or out-of-date software: failed or interrupted reprogramming, incorrect calibration after an update, or a version the manufacturer corrected later.^{[1][2][5][6][8]}
3. 3ECU power supply or earth problems, or low or unstable battery voltage (including spikes from a faulty alternator and damage from a jump start).^[1][2][5][6]
4. 4Moisture or water in the ECU, overheating or physical damage.^[1][6]
5. 5Broken, corroded or frayed ECU wiring or connectors, or CAN bus communication faults.^[3]

• Engine warning light on in the instrument cluster.^[2][5][6]Engine warning light: faults that cause it
• Hard starting or the car does not start.^[1][2][5][6]Hard to start: faults that cause it
• The engine may stall suddenly or cut out at intervals.^[1][2][3][6]Engine stalls: faults that cause it
• Loss of power and poor acceleration.^[1]Less power: faults that cause it
• The car may go into limp-home mode, with performance greatly reduced.^[1]Limp mode: faults that cause it
• Rough running, jerking or misfires.^[1][3][6]Jerking: faults that cause it
• Automatic gearbox that works badly and warning lights for other systems on (ABS, traction control or other modules).^[3][5]
• Several apparently unrelated codes stored at once.^[2]
• Sometimes, at first, no symptom is noticeable.^[3][6]

1. 1Read all the codes and the freeze-frame data with a diagnostic tool and look at the others: voltage codes (P0562, P0563), communication codes (those starting with U) and codes from other control units may be the real cause of the P0606 or a consequence of it.^[2][3][6]
2. 2Check the battery and the charging system first: Carista asks for 12.4 V or more at rest and 13.8 to 14.5 V with the engine running. A low or unstable voltage can be the cause of the code, and it has to be corrected before going further.^[2][6]
3. 3Use a multimeter to check the ECU's power supply and earths, and the condition of its connectors and wiring: corrosion, moisture, damaged terminals, chafed wires.^{[1][2][3][5][6]}
4. 4Autodoc Club suggests starting by resetting the ECU: disconnect the battery for about 30 minutes and then clear the code with the scanner. If the code comes straight back (Carista notes that it usually does while the fault persists), the problem is still there.^[1][2]
5. 5Ask a main dealer about software updates, technical bulletins or ECU campaigns: sometimes the manufacturer fixes it with a reprogramming. As an example, a Volkswagen Group of America bulletin for the 2014 Routan 3.6 (a US case) corrects a P0606 by reprogramming the ECU, asks for any other code to be repaired first and requires the battery to be kept on a charger while programming.^[1][5][6][8]
6. 6Only if the power supply, earths and software are in order and the code persists or returns is the ECU repaired or replaced (new, refurbished or repaired); it must then be programmed and coded for the car with its VIN and equipment.^[1][2][4][6]