Heating combustion chamber, glow plug increases fuel ignitibility and makes fuel in the foggy state easily when engine is cold. Thus, glow plug makes engine starting easily and decreases exhaust gas produced just after turning engine on when engine is cold.
Glow plug control unit(GCU) controls operation of glow plug by PWM with ECTS signal, battery voltage and IG KEY ON signal.
Through glow lamp in cluster, ECM let drivers know if glow plug is ON.
DTC P0684 is set when feedback signal is not normal for 1 sec.
Item
Detecting Condition
Possible Cause
DTC Strategy
Voltage monitoring
Glow plug / control unit circuit error
Faulty GCU
Enable Conditions
IG key ON
Threshold value
Feedback signal is not normal
Diagnosis Time
1 sec.
Fail Safe
Fuel cut
NO
-
EGR Off
Fuel Limit
Check Lamp
OFF
Fig 1) Glow plug is controlled to duty 28% when IG key turns to ON from OFF and cold engine.
Fig 2) Glow plug control signal waveform when IG key turns to ON from OFF and warmed engine.