AutoCodes – GMC – P0642 GMC

P0642 GMC Code - 5 Volt Reference 1 Circuit Low 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: P0642 GMC indicates 5 Volt Reference 1 Circuit Low 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 4,104

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 P0642 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 lower than the expected voltage on any of the 5 Volt reference circuits for greater than 0.5 s.

OBDII Code P0642 GMC - 5 Volt Reference 1 Circuit Low Voltage - AutoCodes.com — P0642 GMC Code - 5 Volt Reference 1 Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P0642 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 P0642 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 P0642 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 P0642 GMC code?

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Need Help with the Code?

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Information for Specific GMC Models

P0642 2014 GMC Sierra — 5 Volt Reference 1 Circuit Low Voltage
P0642 2015 GMC Sierra — 5 Volt Reference 1 Circuit Low Voltage
P0642 2016 GMC Sierra — 5 Volt Reference 1 Circuit Low Voltage
P0642 2017 GMC Sierra — 5 Volt Reference 1 Circuit Low Voltage
P0642 2018 GMC Sierra — 5 Volt Reference 1 Circuit Low 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 P0642 GMC Code

1. What are the common symptoms of OBDII code P0642 GMC?

- Common symptoms include issues with engine performance, rough idling, stalling, and the illumination of the Check Engine Light.

2. What does the OBDII code P0642 GMC "5 Volt Reference 1 Circuit Low Voltage" mean?

- This code indicates that the voltage on the 5-volt reference circuit 1 is lower than expected.

3. What are the potential causes of OBDII code P0642 GMC?

- Possible causes include a faulty engine control module (ECM), damaged wiring or connectors in the 5-volt reference circuit, or a short circuit to ground.

4. How can I diagnose the issue related to OBDII code P0642 GMC?

- Diagnosing this code typically involves checking the voltage on the 5-volt reference circuit, inspecting the wiring and connectors, and testing the ECM for proper function.

5. Can I continue driving my vehicle with OBDII code P0642 GMC present?

- It is not recommended to drive the vehicle with this code present, as it can lead to further damage or engine performance issues.

6. How serious is OBDII code P0642 GMC?

- While the seriousness of the code can vary, it is important to address it promptly to prevent potential damage to the engine or other components.

7. How can I repair OBDII code P0642 GMC?

- Repairing this code may involve replacing the ECM, repairing damaged wiring or connectors, or addressing any short circuits to ground in the 5-volt reference circuit.

8. Can I reset the Check Engine Light after fixing OBDII code P0642 GMC?

- Yes, once the underlying issue causing the code is repaired, the Check Engine Light can be reset using an OBDII scanner.

9. Is it necessary to consult a mechanic for OBDII code P0642 GMC?

- While some DIY enthusiasts may be able to diagnose and repair this code, it is recommended to consult a mechanic for accurate diagnosis and proper repair.

10. How much does it cost to fix OBDII code P0642 GMC?

- The cost of fixing this code can vary depending on the specific issue causing it, but it may involve parts and labor costs ranging from $100 to $500 or more.