P0601 OBD-II: Internal Control Module Memory Check Sum Error

What Does P0601 Code Mean?

OBD-II Code P0601 is defined as a Internal Control Module Memory Check Sum Error

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 P0601 code will be set.

Code P0601 means that the PCM's Memory check sum test is failing. This is a routine self test that is performed periodically through out the day. This is critical because the PCM's Memory Modules store all of the PCM's operating system software as well as its short term operational calculations. 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.

P0601 Symptoms

• Check Engine Light will illuminate
• Failure of Emissions Inspections due to OBD-II Monitor issues
• ABS/Traction Control Light may illuminate
• Vehicle may not perform and/or shift properly
• OBD-II Monitor 'READY' flags go to 'NOT READY' every time key is removed from the ignition
• 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 P0601 Code

• Lack of proper voltage to the PCM
• Defective PCM 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

P0601 Diagnostic Theory for Shops and Technicians

When the code P0601 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is failing its Memory Check Sum self-check and has found errors within its Memory functions. In many cases, the PCM is not getting a high quality, consistent 12 volt power 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 P0601 code, it is important to record any other codes and the P0606 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 P0606 can be difficult to detect.