Fault code P1604 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P1604 – Code Word Unregestered

P1604: Causes, signs and repairs

Error code P1604 is displayed and the check engine light is on - what does this mean?

The DTC P1604 is triggered by the OBD system when a problem is detected with the engine control unit (ECM) or its communication. This manufacturer-specific error code indicates an internal error in the control unit or problems with data transmission between different control units.

What causes can this error code have?

Defective engine control unit (ECM)
Corroded or damaged plug connections on the control unit
Interrupted or short-circuited cable connections
Faulty power supply to the control unit
Defective CAN bus connections
Software errors or corrupt data in the control unit
Electromagnetic interference
Defective ground connections

What symptoms occur in parallel with error code P1604?

Starting problems: The vehicle is difficult or impossible to start
Irregular engine running: Engine runs unevenly or stutters
Loss of power: Reduced engine power and poor acceleration
Emergency running program: Engine only runs in emergency running mode with limited power
Other fault codes: Additional trouble codes are saved
Communication error: Diagnostic device cannot communicate with the ECM

How can the P1604 fault code problem be rectified?

Repairing the P1604 fault code requires a systematic approach to identify the root cause.
Checking and cleaning all plug connections on the engine control unit and replacing corroded plugs and pins
Measuring the power supply to the ECM and repairing defective circuits or replacing the main fuse
Checking and repairing the control unit's earth connections by cleaning the contacts and connecting them securely
Software update or reprogramming of the engine control unit by a specialist company with the appropriate equipment
Replacement of the defective engine control unit and subsequent coding to the vehicle
Checking and repairing the CAN bus lines by testing continuity and replacing damaged cables

FAQ - Frequently asked questions about DTC P1604

Can I continue driving with error code P1604?

Continuing to drive with EOBD code P1604 is not recommended, as the engine control unit may not function properly. This can lead to unpredictable engine behavior or complete failure.

How much does it cost to repair error code P1604?

Repair costs vary depending on the cause: simple plug problems cost 50-150 euros, software updates 100-300 euros, while a new engine control unit can cost 800-2500 euros.

Can I repair error code P1604 myself?

You can carry out basic checks such as plug connections and fuses yourself. However, work on the control unit or software updates should be carried out by specialists.

How long does it take to diagnose error code P1604?

A professional diagnosis usually takes 1-3 hours, depending on the complexity of the problem and the diagnostic equipment available.

Does error code P1604 occur more frequently in certain weather conditions?

Yes, moisture and extreme temperatures can affect connectors and electronic components, making the code more common in wet or very cold weather.

Can a low battery cause error code P1604?

A weak or faulty battery can lead to voltage fluctuations that can affect the engine control unit and trigger the P1604 code.

Vehicles in which error code P1604 occurs most frequently

Error code P1604 is a manufacturer-specific DTC that mainly occurs when there are electronic problems with the engine control unit and can affect various vehicle brands, but is most common in the following vehicles:

Ford: Focus, Fiesta, Mondeo, Transit (2005-2015)
Mazda: 3, 6, CX-5, MX-5 (2008-2016)
Volvo: S60, V70, XC90, S80 (2004-2012)
Jaguar: XF, XJ, F-Type, XE (2009-2017)
Land Rover: Discovery, Range Rover, Freelander (2006-2014)
Lincoln: MKZ, Navigator, Continental (2007-2016)

If the code P1604 occurs in your vehicle, it is important to carry out a thorough diagnosis first before initiating expensive repairs. Many problems can be solved by simple measures such as cleaning plug connections or software updates. For more complex problems, however, you should visit a qualified mechanic who has the necessary equipment and experience.

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