Because thermal efficiency of electronically controlled diesel engine is higher than that of gasoline engine, heat loss to cylinder wall is lower. This enables electronically controlled diesel engine to generate high power and have high fuel efficiency. However in other point of view, due to low engine coolant temperature, heating efficiency lowered then, driver is unsatisfied with the heating. To cope with this situation, PTC heater is installed in coolant line and it raises heating efficiency and raise coolant temperature.

【 PTC heater relay ON condition】

When one of the following condition is met at engine rpm is over 600rpm and battery voltage is over 10.5V.

☞ If IATS is below -20℃, ON until coolant temperature reaches 80℃± 10℃.

☞ If IATS is below -5℃, ON until coolant temperature reaches 75℃± 10℃

☞ If IATS is below 10℃, ON until coolant temperature reaches 70℃± 10℃.

☞ If IATS is below 20℃, ON until coolant temperature reaches -10℃~ 10℃.

P1634 is set when excessive current or "0"A is detected in PTC heater relay #1 control circuit for more than 1.0 sec. at PTC heater relay operating condition. This code is due to 1) open or 2) short to battery or ground in PTC heater relay #1 control circuit or 3) component problem.