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P0605 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Internal Control Module ROM Error (Module Identification Defined by SAE J1979)


The Engine Control Module (ECM) controls key vehicle functionalities like fuel injection and ignition timing, Anti-lock Braking Systems (ABS), traction control, power steering, radiator control, emission control, and tasks like window up-down, controlling the radio and the horn.

Your vehicle’s Read-Only Memory (ROM) part consists of parameters the ECM stores that cannot be erased. The parameters include ECM tests and numeric ranges set by the Original Equipment Manufacturer (OEM) that the ECM permanently stores and refers to while your vehicle is running. These parameters are guidelines and instructions of how the ECM should interpret the OBD codes and the values gauged from various sensors like the interior buttons, oxygen sensors, Mass Air Flow (MAF) sensors, etc.

If the information sent from these sensors to the ECM does not match the values stored in the ROM by the OEM, the Check Engine Light will be on. If the memory stored in the ECM has been erased or deleted, a P0605 code occurs.

The ECM is like a computer that runs your vehicle. It needs instructions on what to perform, the correct values for each sensor, and so on.  However, when this data is lost, the ECM does not know what to do and throws the P0605 code.


The following is a list of reasons that might display this code:

  • Faulty or interrupted ECM ground or power supply
  • Faulty solder point(s) on the PCBs of the ECM from heat or vibrations
  • Loss of memory of the ROM in the ECM
  • ECM may need an update or may need to be re-flashed
  • Programming the ECM with an aftermarket performance programmer


  • A Check Engine Light shows up
  • Your vehicle’s engine might misfire
  • Your vehicle’s engine might stall or not start

Some of these symptoms might appear even before a Check Engine Light shows up.


We suggest you take your vehicle to a qualified technician to check your car thoroughly.

  • Check the OEM Technical Service Bulletins (TSB’s), and any recalls to determine if the ECM needs any update, re-flash, or reprogramming.
  • Thoroughly check the wires connecting the ECM and various solder points
  • Thoroughly check the ECM
  • Test the ECM thoroughly for proper ground points and proper power supplies

Ensure that they clear the code, drive the vehicle for a sufficient time to make sure the code is thrown again by the PCM

Common mistakes

Failing to thoroughly check whether there is an OEM TSB or any recalls related to your vehicle for updating, re-flashing, or reprogramming the ECM

Changing the ECM without thoroughly checking the solder points, power supply, and grounds in the ECM

How Serious Is This Code?

The code is critical, and vehicle owners should fix it as soon as possible because it stops the ECM from identifying other codes. If the ROM of the ECM is erased for some reason, it means that your vehicle’s ECM can no longer identify other codes, which will impact your car. It could also mean that your car may fail to run correctly as the ECM controls key vehicle functionalities like fuel injection and ignition timing, etc.

What repairs can fix the code?

We advise you to take your vehicle to the nearest mechanic as this is not a “do-it-yourself” task. We strongly recommend you go to a garage/mechanic who can check OEM TSB or recalls, reprogram the ECM.

  • Re-flashing or installing a new ECM involves special tools to program the vehicle’s Vehicle Identification Number (VIN) and/or anti-theft information.
  • Check for any OEM TSBs or recall-related information that might update your ECM with updated software.
  • Check for any faulty wiring, ground, and power supply.
  • Replace the ECM

Related codes



The ECM is a specialized part; consult a dealership or a workshop to check the wiring properly and reflash the ECM if needed.

To get an advanced scan and thorough check, consult a qualified mechanic. 

P0605 – What Does It Mean and How To Fix It