AutoCodes – GMC – P0643 GMC

P0643 GMC Code - 5 Volt Reference 1 Circuit High Voltage

Quick Answer

The Engine Control Module (ECM) has four (4) internal 5 Volt reference circuits (Some models have two (2) internal 5 Volt reference circuits). Common causes include Faulty Sensor on 5 Volt circuit, Sensor on 5 Volt circuit harness is open or shorted, Sensor on 5 Volt 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: P0643 GMC indicates 5 Volt Reference 1 Circuit High Voltage.
Common causes: Common causes include Faulty Sensor on 5 Volt circuit, Sensor on 5 Volt circuit harness is open or shorted, Sensor on 5 Volt 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 2,802

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 Jul 17, 2022

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0643 GMC Description

The Engine Control Module (ECM) has four (4) internal 5 Volt reference circuits (Some models have two (2) internal 5 Volt reference circuits). Each internal reference circuit provides external 5 Volt reference circuits for more than one sensor. A short to ground or short to voltage on one external 5 Volt reference circuit can affect all the components connected to the same internal 5 Volt reference circuit. The Diagnostic Trouble Code (DTC) will be set when the ECM detects a higher than the expected voltage on any of the 5 Volt reference circuits for greater than 0.5 s.

OBDII Code P0643 GMC - 5 Volt Reference 1 Circuit High Voltage - AutoCodes.com — P0643 GMC Code - 5 Volt Reference 1 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0643 GMC?

Faulty Sensor on 5 Volt circuit
Sensor on 5 Volt circuit harness is open or shorted
Sensor on 5 Volt circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P0643 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 does this mean?

Code Tech Notes

Disconnecting one component at a time from the affected 5 Volt reference circuit while observing the scan tool 5 Volt Reference Circuit Status parameter may help locate the fault. The scan tool parameter will change from Malfunction to OK when the source of the fault is disconnected. If all 5 Volt reference components have been disconnected and a fault is still indicated, the fault may exist in the wiring harness.

The 5 Volt reference 1 circuit provides 5 Volt to the following sensors: (Some models may have different sensors, please consult the factory service manual for the list of sensors for your model and year)

- Air conditioning (A/C) refrigerant pressure sensor
- Camshaft position sensor
- Engine oil pressure sensor
- Fuel pressure sensor
- Fuel rail pressure sensor
- Fuel tank pressure sensor
- Multifunction intake air sensor

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0643 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 P0643 GMC code?

Need more information on how to fix the P0643 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0643 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P0643 2014 GMC Sierra — 5 Volt Reference 1 Circuit High Voltage
P0643 2015 GMC Sierra — 5 Volt Reference 1 Circuit High Voltage
P0643 2016 GMC Sierra — 5 Volt Reference 1 Circuit High Voltage
P0643 2017 GMC Sierra — 5 Volt Reference 1 Circuit High Voltage
P0643 2018 GMC Sierra — 5 Volt Reference 1 Circuit High Voltage

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 P0643 GMC Code

1. What are the common symptoms of OBDII code P0643 GMC (5 Volt Reference 1 Circuit High Voltage)?

The common symptoms include engine stalling, rough idling, poor acceleration, and potential illumination of the Check Engine Light.

2. What can cause OBDII code P0643 GMC to trigger?

Possible causes of this code include a faulty Engine Control Module (ECM), damaged wiring or connectors in the 5-volt reference circuit, or a short circuit in the sensor connected to the circuit.

3. How serious is OBDII code P0643 GMC?

While the severity can vary, it is important to address this code promptly as it can lead to drivability issues and potential damage to other engine components if left unresolved.

4. How can I diagnose OBDII code P0643 GMC?

Diagnosis typically involves using a scan tool to read the code, checking the 5-volt reference circuit for voltage irregularities, inspecting wiring and connectors for damage, and testing the sensors connected to the circuit.

5. Can I drive my vehicle with OBDII code P0643 GMC active?

It is not recommended to drive your vehicle with this code active, as it can lead to performance issues and potential further damage to the engine.

6. What are some repair tips for fixing OBDII code P0643 GMC?

Repair options may include repairing or replacing damaged wiring or connectors, replacing the faulty sensor, or in some cases, replacing the Engine Control Module (ECM).

7. Can a DIY enthusiast fix OBDII code P0643 GMC?

While some experienced DIY enthusiasts may be able to address this issue, it is recommended to seek professional help, especially for diagnosing and repairing wiring or ECM-related problems.

8. How much does it cost to fix OBDII code P0643 GMC?

The cost of fixing this code can vary depending on the underlying cause, parts needed for repair, and labor costs. It is advisable to get a professional diagnosis to determine the exact repair cost.

9. Will clearing the OBDII code P0643 GMC make it go away permanently?

Clearing the code without addressing the underlying issue will not make it disappear permanently. The problem causing the code needs to be diagnosed and fixed to prevent it from reoccurring.

10. How can I prevent OBDII code P0643 GMC from coming back?

Regular vehicle maintenance, checking and replacing damaged wiring or connectors promptly, and addressing any related engine issues can help prevent the recurrence of this code.