Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
ROM (Read Only Memory)
ROM stores the program memory, i.e. what the CPU is to do, such as switch on interior lighting when the door is opened. ROM is not volatile and is not affected by loss of power. It can sometimes be SPS programmed. In a home computer, ROM is stored on the hard drive, which can hold several GB. In a vehicle control module (vehicle computer), ROM is often only a few hundred KB.
If battery voltage becomes too low during reprogramming, only part of the program will be downloaded to ROM. If this occurs, there is a risk that the control module will lock up and not respond to new instructions from the diagnostic tool.
The diagnostic tool can be used to read system information from the control module. New program versions may have modified or improved properties. Stay informed on which new programs have come out on TIS to avoid unnecessary tracing of a fault that is software-related.
In addition to being stored in the program memory, certain other data is also stored in ROM. In a control module, for example, you can go in under the Adjustments menu of the diagnostic tool and make a change so that the doors lock when you driver faster than a certain speed. This is stored in ROM, not RAM, so that the function does not disappear if the customer replaces the car battery. All values in the diagnostic tool Adjustments menu are stored in ROM for this reason.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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