B1240 Code: Meaning, Causes, and Symptoms | OBD2 Codes

B1240 – Start Button Mode Indicator Circuit Short

 

B1240 Possible Symptoms

 

Engine Light ON (or Service Engine Soon Warning Light)

 

B1240 Possible Causes

 

Faulty Start/Stop Switch Indicator,Start/Stop Switch Indicator harness is open or shorted,Start/Stop Switch Indicator circuit poor electrical connection,Faulty Body Control Module (BCM)

 

B1240 Description

 

The Body Control Module (BCM) uses a Field Effect Transistor (FET) as circuit protection for the start/stop switch indicator and as an electronic switch to turn the start/stop switch indicator on and off. The FET receives fused battery voltage from BCM. When the start/stop switch is pressed a voltage and ground signal are sent to the BCM. When the vehicle enters RUN or START mode, the BCM forward biases the FET which provides voltage to the amber LED in the start/stop switch, illuminating the word ENGINE.