A malfunction is detected by using a checksum technique 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. During normal operation the microcontroller is monitored when the following test conditions have been fulfiled if there is overrun :
① No start present
② Accelerator pedal not actuated
③ Cruise control is not active
④ No increasing external fuel quantity command
The ECM will set a code if an error is detected in the ECM’s microcontroller malfunction during two driving cycles.
DTC NO. | Detecting Condition | Possible Cause |
P 1638 | ● P 1638 ① Error is recognized if the microcontroller is reported finally defective (Rcovery (new program start) occurred) ② Error is recognized if the injector is energzied when the engine speed is above the engine speed 2050 rpm and APS is 0 % with the range of fuel cut ③ Error is recognized if the engine speed is not drop below 500 rpm within 1.5 sec. after turning the ignition switch off (Watchdog after run test) ④ Gate array communication error ● 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 start in case of the detecting condition No.① | ECM |
