Intialization of the background test is the first one carried out in the system. It therefore starts in the internal ROM and leads to supervisor identification by testing and initializing the external bus and testing the internal RAM. Afterwards the external RAM is tested and the checksum of the EPROM is calculated. After starting, A/D converter with all electric connections are monitored continuously by the ECM. 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.
The ECM will set a code if an error is detected in the ECM’s monitoring ADC malfunction during two driving cycles.
DTC NO. | Detecting Condition | Possible Cause |
P 1639 | ● P 1639 ① Error is recognized if the RAM test wrong (Dynamic RAM test failed) ② Error is recognized if the APS 2 signal is above 200.39 mV when checking the ground connection every 2 second ③ Error is recognized if the voltage 1,2 of sensor supply is above 5.16 V or below 4.7 V ● Engine Condition : IG ON ● Fuel Limit : YES ● Fuel Cut : NO ● EGR OFF : NO ● MIL : NO ● LIMP HOME MODE Engine speed is fixed as 1200 rpm without pedal sensor action. | ECM |
