Fault code P0604 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P0604 – Internal Control Module Random Access Memory (RAM) Error

P0604: Causes, signs and repairs

Error code P0604 is displayed and the check engine light is on - what does this mean?

The DTC P0604 signals an internal error in the engine control unit (ECU/PCM), where the OBD system has detected a defect in the memory or in the processing logic of the control unit. This trouble code indicates serious problems with the central engine control unit and may have slightly different definitions for different manufacturers.

What causes can this error code have?

Defective engine control unit (ECU/PCM)
Corrupt software or firmware in the control unit
Memory error in the EEPROM or RAM of the control unit
Voltage fluctuations or power supply problems
Overheating of the engine control unit
Water damage to the control unit
Electromagnetic interference
Faulty ground connections to the control unit

What symptoms occur in parallel with fault code P0604?

Starting problems: The vehicle is difficult or impossible to start
Engine misfires: Irregular engine running and jerky driving
Loss of power: Significantly reduced engine power
Emergency running program: Engine only runs in emergency mode with limited power
Complete engine failure: Engine no longer starts
Irregular idling speed: Idle speed fluctuates or is too high/low
Transmission shifting problems: Shifting problems may occur with automatic transmissions

How to fix the problem of fault code P0604?

Repairing fault code P0604 usually requires professional diagnosis, as these are critical ECU problems.
Carry out a software update: Program control unit with current firmware and reset basic settings
Check the power supply: Check and repair battery, alternator and all power supply lines to the control unit
Replace earth connections: Clean, tighten or completely replace all earth cables to the ECU
Replace control unit: Replace defective engine control unit with a new or overhauled unit and have it programmed
Check wiring harness: Check the entire wiring harness to the control unit for damage, corrosion or short circuits
Dry the control unit: In the event of water damage, have the control unit professionally dried and the contacts cleaned

FAQ - Frequently asked questions about DTC P0604

Can I continue driving with error code P0604?

No, you should not continue driving with code P0604. This EOBD error indicates critical problems with the engine control unit, which can lead to sudden engine failure.

How much does it cost to repair error code P0604?

The costs vary greatly depending on the cause: software update 100-200€, cable repairs 150-400€, new control unit 800-2500€ plus programming.

Is P0604 a permanent or sporadic error code?

P0604 is usually a permanent error, as it indicates hardware defects in the control unit. Sporadic occurrence can indicate voltage problems or loose connections.

Can other error codes occur together with P0604?

Yes, additional codes such as P0601, P0602, P0603 or various sensor error codes often occur, as the defective control unit cannot monitor other systems correctly.

How long does it take to diagnose and repair P0604?

The diagnosis takes 1-2 hours, a software update 2-3 hours, the ECU replacement can take 4-8 hours.

Can P0604 be caused by a weak battery?

Yes, a weak or faulty battery can cause voltage fluctuations that can damage the control unit and trigger the error code P0604.

Vehicles in which fault code P0604 occurs most frequently

Error code P0604 is a critical control unit error and can occur in various vehicle brands, but is most common in the following vehicles:

BMW: 3 Series E46, 5 Series E39/E60, X3 E83, X5 E53 (2000-2010)
Mercedes-Benz: C-Class W203/W204, E-Class W211, ML W163/W164 (2001-2012)
Audi: A4 B6/B7, A6 C5/C6, Q7 4L (2000-2011)
Volkswagen: Golf IV/V/VI, Passat B5/B6, Touareg 7L (1999-2014)
Ford: Focus II/III, Mondeo III/IV, S-Max, Galaxy (2004-2015)
Opel: Astra H, Vectra C, Insignia A, Zafira B (2004-2016)
Renault: Megane II/III, Laguna II/III, Scenic II/III (2002-2014)
Peugeot: 307, 308, 407, 508, 3008 (2001-2015)
Citroën: C4, C5, C8, Picasso (2004-2016)
If the code P0604 occurs in your vehicle, you should visit a specialist workshop immediately, as this is a critical control unit error. A quick diagnosis can prevent expensive consequential damage and ensure safety. Avoid driving with this error code, as a complete engine failure can occur while driving.

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