P0605 - OBD II Trouble Code

Auto Systems and Repair

Internal Control Module Read Only Memory (ROM) Error

Our emissions expert has put together the following information about the P0605 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

  • OBD II P0605

Fault Code Definition

  • Internal Control Module Read Only Memory (ROM) Error
What does this mean?
The PCM or Power Train Control Module performs many vital functions in a modern vehicle, such as management of the Fuel System, Ignition System, Transmission, Anti-Lock Brake and Traction Control systems. The PCM regularly runs a self-diagnosis function where it performs normal mathematical calculations, and if the results of these calculations are not as expected, a code such as P0605 code will be set. 

Code P0605 means that the PCM's Read Only Memory (ROM) section is not passing its routine self test. This is critical because the ROM stores all of the PCM's operating system software. If this part of the PCM's functionality is unreliable, the powertrain's main computer can't be trusted to accurately do its job and may need to be replaced.   

Symptoms

  • Check Engine Light will illuminate
  • Emissions Inspection failure  
  • ABS/Traction Control Light may illuminate
  • Vehicle may not perform and/or shift properly
  • Decrease in fuel economy
  • In unusual cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems, such as dying when coming to a stop and/or misfire-like symptoms

Common Problems That Trigger the P0605 Code

  • Lack of proper voltage and/or ground to the PCM  
  • Defective PCM ROM memory module
  • Defective PCM ground circuit(s)
  • Defective PCM controlled output devices

Common Misdiagnoses

  • PCM is replaced when the root cause is improper voltage to the PCM
  • PCM is replaced when the root cause is defective PCM ground circuits

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog 

P0605 Diagnostic Theory for Shops and Technicians
When the code P0605 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is failing its Read Only Memory (ROM) self-check and has found errors within its Read Only Memory functions.  In many cases, the PCM is not getting a high quality, consistent 12 volt power and ground signal. However in some cases, actual Memory modules are defective and the PCM needs to replaced and re-programmed.  But, before you replace the PCM, be sure to check for any shorted output devices that may have cause the Memory functions to fail. 

When diagnosing a P0605 code, it is important to record any other codes and the P0605 freeze frame data. Then one should duplicate the code setting conditions with a test drive. Pay close attention to the engine load, throttle position, RPM, and road speed because a P0605 can be difficult to detect.

 

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