if I pull the cable off to test battery will it mess up the computer system
It shouldn’t if the car is off. Are you just using a multimeter? I was just checking my batteries last week and didn’t disconnect them to check the voltage
By removing the negative battery cable, you’re going to lose all the readiness monitors and radio presets, even if the ignition is off
I wouldn’t exactly say it will “mess up the computer system” . . . but it will affect operation for a short while, and the truck won’t be ready for smog inspection, either
If you are asking “Can I remove a battery cable while the engine is running to test the charging system”.
No…do not do this. This can put a power surge to the computer and damage it.
Most auto parts stores will check your charging system for free. Just be sure they are not swamped with other customers at the time.
There’s various gadgets available you can use to prevent the computer from forgetting its stored parameters and readiness monitors when the battery is disconnected. Google “memory saver”. When you are ready to remove the battery, make sure everything is turned off, keys in your pocket, doors closed so no inside lights are on. Wait for 15 minutes for the computers to all shut down. Disconnect the negative battery terminal first. Then the positive. When re-installing the battery, again make sure everything is turned off, doors closed, then connect the + terminal first, and the negative terminal last.