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.
Diagnostics And Services: Parameters
Parameters or values are data that are read out from the control module's memory positions to, e. g., check the signal from a sensor or identify the control module's software version.
In principle, parameters can be divided into two parts:
- one for dynamic values continuously updated in the control module
- one for static values not changed by the control module and always stored.
Parameters, dynamic
The dynamic values are stored in the control module's RAM-memory, which means that the values disappear when the memory's power supply is turned off (control module is turned off). As soon as the control module's power is turned on (ignition on), values are stored again.
Example of values are:
- Outside temperature
- Engine speed
- Load
- Coolant temperature
- Vehicle speed
- Battery voltage
Values are updated continuously after a pre-determined time interval. This means that certain values are updated with very short time interval, while other values are updated more seldom. Update rate is determined by how important the value is to the control module.
By reading off the value from, e. g., a sensor or switch, it can be decided if the signal is correct or not.
When a malfunction is detected and a diagnostic trouble code is stored, it may well be that the displayed value is a replacement value and not the real value. If the value does not change, e. g., if the sensor is disconnected, it may be the replacement value that is shown.
Parameters, static
The static values are stored in the control module's EEPROM, which means that these values are always stored regardless of if the control module is on or off. These values are normally not updated by the control module, instead they are only changed using, e. g., the diagnostics tool at vehicle manufacture in the factory or reprogramming during a workshop visit.
Example of values are:
- Hardware P/N (control module without software).
- Hardware serial number (control module without software).
- Software P/N.
- Diagnostic software P/N.
- Customer-programmed values, e. g., passenger compartment temperature, alarm on and off.
- The vehicle's configuration, that is, the vehicle's content and equipment that can be used to compare the vehicle's equipment physically with how the vehicle is configured. The configuration may be affected/changed, e. g., when downloading software.
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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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