Malfunctions are detected using checksum techniques for verifying data. Digital data is composed of zeros and ones. A checksum is the total of all ones in a string of data. By comparing the checksum value with a stored value, a malfunction can be detected. If an overrun occurs during normal operation, the microcontroller will be monitored when the following test conditions have been fulfiled :
① Ignition start has not occurred
② Accelerator pedal not actuated
③ Cruise control is not active
④ No increase in external fuel quantity command
The ECM will set a DTC code if it detects a malfunction in the ECM’s microcontroller during two driving cycles.
DTC NO. | Detecting Condition | Possible Cause |
P 1638 | An error will occur : ① If the microcontroller is reported as defective(Recovery occurred (new program start)) ② If the injector is energized while engine speed is above 2050 rpm and APS is 0 % within the range of fuel cut ③ If the engine speed has not dropped below 500 rpm within 1.5 sec. after turning the iginition switch off (Watchdog post-run test) ④ If a Gate array communication error occurs ● Engine Condition : IG ON (①,②,④) IG OFF(③) ● Fuel Limit : NO (①,②,④) YES (③) ● Fuel Cut : YES (①,②,④) ● EGR OFF : NO ● MIL : NO ● LIMP HOME MODE Engine speed is not relative in case of the detecting condition No.① | ECM |
