In order to diagnose and remove fault, connect Fcar ECU code reader to diagnostic socket of vehicle, as shown in Pic.4-37.It has special functions as follow, such as engine off-cylinder running, test injection solenoid valve response time, calibrate and replace injector, take rapid sample of engine data, user can limitedly alter ECU program etc. under engine manufacturer restricted working condition or characteristic parameter.
Maintenance technician can use Fcar vehicle code reader to enter ECU memory, monitor sensor output, read DTC, And also selectively program options that already exists in system.Now I'll tell you how to use auto scanner diagnose ECU.
How to use ECU code reader diagnose a ECU
All electronically controlled engines will save DTCs in ECU memory after sensor out of normal operating range. When problems monitored, they will be sent back to ECU, some serious problems will cause yellow or red diagnostic light on instrument panel lighten, when yellow light on, power and RPM of engine will reduce; when red light on, indicates the problem that sensor detected is serious. If ECU has stop control function, then this function will be triggered. Some electronic control system has diagnosis trigger switch, if operate this switch, check engine light on instrument panel will blink, for driver and maintenance technician to read flashing DTC. Some electronic control systems need use jumper to short circuit two terminals in diagnostic connector, to display DTC saved in ECU through flashing of diagnostic light of instrument panel. Pic. 4-35（a）shows a 12-pin diagnostic data connector（DDL）, DDL connector normally located in truck cab(the specific position determined by manufacturer, this is a special case of Detroit DDEC I system or DDEC II system, but DDEC Ⅲ system and DDECⅣ system no longer adopt this kind of connector).
In order to flashing display DTC, ignition switch are required to turn off (in OFF) and insert jumper between terminal A and M which are marked clearly on connector. Pic. 4-35（b）shows an example of interpreting flashing DTC, taking DDEC I system or DDEC II system as example, flash code 13 means coolant level sensor has detected coolant level too low, flash code 21 indicates throttle position sensor has detected circuit voltage too high.
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