Computers

s Use inputs to control outputs

Inputs s Most are from sensors s Will usually be either an analog or digital voltage s Most will supply an input similar to a potentiometer or have a varying frequency AC or DC signal

Input types s Insert sensor types here but shorten

Specific inputs s Insert sensors here but shorten

Trouble codes s A code stored in a computer to identify a specific type of fault s Indication that something has gone outside of normal operating parameters for a specific period of time s A function of the computer’s self diagnostic capabilities

OBD1 (on-board diagnostics one) s Began in late 1970s but was not made mandatory by federal govt. until 1990s s Required all vehicles to perform self diagnostics to identify some major failures that can cause excessive emissions s Most trouble codes could be flashed out on an indicator lamp

OBD2 (on-board diagnostics two) s Started appearing in 1994 and made mandatory on most vehicles in 1996 s Requires all vehicles to identify any failure that will result in exceeding the FTP by 1.5% – This includes identifying old catalytic converters, missfires, and evaporative systems failures

OBD2 s Trouble codes are now universal and require the use of a scan tool to read s DLC is now universal

Trouble code access s Can be gained by various methods: – Grounding a wire and counting flashes of bulb – Grounding a wire and counting pulses of volt meter – Unplugging the coolant temperature sensor and counting flashes

Trouble code access s Can be gained by various methods: – Cycling the key on and off three times and counting the flashes – Through the data stream via a scan tool

Trouble code types s Current vs. History – Just because the light is on does not mean problem is occurring s Hard vs. Soft

Trouble code diagnosis s If problem is occurring; use published diagnostics and grey matter s If problem is not occurring; the published diagnostics and charts can help but in almost every case can not be used directly s If a vehicle has multiple codes, look for commonalties s One malfunction can set multiple codes

The End