AutoCodes – Generic – B1240

B1240 Code - Start Button Mode Indicator Circuit Short

Quick Answer

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. Common causes include Faulty Start/Stop Switch Indicator, Start/Stop Switch Indicator harness is open or shorted, Start/Stop Switch Indicator circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: B1240 indicates Start Button Mode Indicator Circuit Short.
Common causes: Common causes include Faulty Start/Stop Switch Indicator, Start/Stop Switch Indicator harness is open or shorted, Start/Stop Switch Indicator circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 11,061

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 04, 2019

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
Comments
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Code 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.

OBDII Code B1240 - Start Button Mode Indicator Circuit Short - AutoCodes.com — B1240 Code - Start Button Mode Indicator Circuit Short

What does this mean?

What are the Possible Causes of the DTC B1240?

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)

How to Fix the DTC B1240?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

B1240:11 Start Button Mode Indicator Circuit Short to Ground
B1240:15 Start Button Mode Indicator Circuit Short to Battery or Open

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B1240 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Information for Specific Makes

B1240 Acura — Problem In The Mode Control Linkage, Doors, Or Motor Circuit
B1240 Ford — Start Button Mode Indicator Circuit Short
B1240 Honda — Problem In The Mode Control Linkage, Doors, Or Motor Circuit
B1240 Lincoln — Start Button Mode Indicator Circuit Short
B1240 Mercury — Start Button Mode Indicator Circuit Short

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.