Computers

Computers

Use inputs to control outputs

Inputs

Most are from sensors Will usually be either an analog or

digital voltage Most will supply an input similar to a

potentiometer or have a varying frequency AC or DC signal

Input types

Insert sensor types here but shorten

Specific inputs

Insert sensors here but shorten

Trouble codes

A code stored in a computer to identify a specific type of fault

Indication that something has gone outside of normal operating parameters for a specific period of time

A function of the computer’s self diagnostic capabilities

OBD1 (on-board diagnostics one)

Began in late 1970s but was not made mandatory by federal govt. until 1990s

Required all vehicles to perform self diagnostics to identify some major failures that can cause excessive emissions

Most trouble codes could be flashed out on an indicator lamp

OBD2 (on-board diagnostics two)

Started appearing in 1994 and made mandatory on most vehicles in 1996

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

Trouble codes are now universal and require the use of a scan tool to read

DLC is now universal

Trouble code access

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

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

Current vs. History– Just because the light is on does not mean

problem is occurring Hard vs. Soft

Trouble code diagnosis

If problem is occurring; use published diagnostics and grey matter

If problem is not occurring; the published diagnostics and charts can help but in almost every case can not be used directly

If a vehicle has multiple codes, look for commonalties

One malfunction can set multiple codes

The End