AutoCodes – GMC – P305C GMC

P305C GMC Code - DC/DC Converter Ignition On/Start Switch Circuit Low Voltage

Quick Answer

The Body Control Module (BCM) controls the ignition main relay through the control circuit by applying voltage to the circuit. Common causes include Faulty Power Supply Transformer, Power Supply Transformer harness is open or shorted, Power Supply Transformer 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: P305C GMC indicates DC/DC Converter Ignition On/Start Switch Circuit Low Voltage.
Common causes: Common causes include Faulty Power Supply Transformer, Power Supply Transformer harness is open or shorted, Power Supply Transformer 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 2,834

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 May 16, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P305C GMC Description

The Body Control Module (BCM) controls the ignition main relay through the control circuit by applying voltage to the circuit. The power supply transformer samples the system voltage on the Ignition 1 voltage circuit from the ignition main relay. If the Power Supply Transformer detects a fault in the circuit it will request the Engine Control Module (ECM) to set the Diagnostic Trouble Code (DTC) and illuminate the Malfunction Indicator Light/Lamp (MIL).

OBDII Code P305C GMC - DC/DC Converter Ignition On/Start Switch Circuit Low Voltage - AutoCodes.com — P305C GMC Code - DC/DC Converter Ignition On/Start Switch Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P305C GMC?

Faulty Power Supply Transformer
Power Supply Transformer harness is open or shorted
Power Supply Transformer circuit poor electrical connection

How to Fix the DTC P305C GMC?

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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P305C GMC 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.

Need more information about the P305C GMC code?

Need more information on how to fix the P305C GMC code? Get Access to Factory Service Manuals

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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.

Frequently Asked Questions about P305C GMC Code

1. What are common symptoms of OBDII code P305C in a GMC vehicle?

- Common symptoms include difficulty starting the vehicle, rough idling, poor engine performance, and illumination of the check engine light.

2. What does the OBDII code P305C GMC indicate?

- The code P305C indicates a low voltage condition in the DC/DC Converter Ignition On/Start Switch Circuit.

3. What are possible causes of the P305C code in a GMC vehicle?

- Possible causes include a faulty DC/DC converter, a problem with the ignition on/start switch circuit, damaged wiring or connectors, or a weak battery.

4. How can I diagnose the P305C code in my GMC vehicle?

- To diagnose the P305C code, you may need to perform a thorough inspection of the DC/DC converter, check the ignition on/start switch circuit for continuity, and test the battery voltage.

5. Can I still drive my GMC vehicle with the P305C trouble code?

- It is not recommended to drive your vehicle with the P305C code present, as it can lead to further damage and potential safety hazards.

6. How do I repair the DC/DC Converter Ignition On/Start Switch Circuit Low Voltage issue in my GMC vehicle?

- Repairing the issue may involve replacing a faulty DC/DC converter, repairing or replacing damaged wiring or connectors, or addressing any issues with the ignition on/start switch circuit.

7. Will resetting the trouble codes make the P305C code disappear?

- Resetting the trouble codes may temporarily clear the P305C code, but if the underlying issue is not addressed, the code is likely to reappear.

8. Is it safe to continue driving my GMC vehicle if the P305C code comes and goes?

- It is not recommended to ignore intermittent occurrences of the P305C code, as it can indicate an ongoing issue that needs to be resolved to ensure proper vehicle operation.

9. Can a DIY enthusiast fix the P305C code issue in a GMC vehicle?

- Depending on your knowledge and experience with automotive repairs, you may be able to address the P305C code yourself by following diagnostic procedures and making necessary repairs.

10. How long does it typically take to repair the DC/DC Converter Ignition On/Start Switch Circuit Low Voltage issue?

- The repair time can vary depending on the exact cause of the issue and the complexity of the repairs needed. It is best to consult a professional mechanic for an accurate estimate.