Testing Computers

Testing the following items will assist you in deciding if the computer needs to be replaced:

• Test all power feeds to the computer, most computers have at least two power feeds. One power feed is constant battery power, the other is switched ignition power.
• • Check the voltage level on each power feed with a digital multimeter; make sure the voltage level is the same on each power feed (close to battery voltage). If it is not, check the wiring to the computer for poor connections, shorts, and open circuits.
  • Check for adequate current delivery to each power feed with a low resistance test light. The test light should be bright an all power feeds. If the light is dim on any circuit, check the wiring to the computer for poor connections, shorts, and open circuits.
• Check the voltage level on all ground connections at the computer, most computers have at least two ground connections.
• • Check the voltage level on each ground connection with a digital multimeter connected to battery negative; make sure the voltage level is the same on each power feed (close to zero volts). If it is not, check the wiring to the computer for poor connections, shorts, and open circuits.
• Check all input signals. Most computers have several input signals, some have dozens. Make sure the input signal voltage is within specification for the associated input device. If it is not within specifications, check the following:
• • Check the wiring from the input device to the computer for poor connections, shorts, and open circuits.
  • Check each input device for proper operation.
• Check all output circuits. Most computers have several output signals, some have dozens. Make sure the output signal voltage is within specification for the associated output device. If it is not within specifications, check the following:
• • Check the wiring from the output device to the computer for poor connections, shorts, and open circuits.
  • Check each output device for proper operation.
  • Check each output device for proper internal resistance. Output devices with low internal resistances can cause the computer to shut down that circuit or to not operate correctly.
• Check all connections at the computer. Check for:
• • Proper terminal-to-terminal tension.
  • Proper terminal-to wire connection.
  • Proper pin length on the computer's own connectors.
  • Check for dirty or corroded connections.

If everything connected to the computer is functioning correctly, but the computer is still not functioning correctly, the computer must be bad. This process of decision-making is called deduction.