AutoCodes – GMC – P159F GMC

P159F GMC Code - Fuel Economy Mode Switch Circuit Low Voltage

Quick Answer

The Engine Control Module (ECM) supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the S87 fuel economy mode switch. Common causes include Faulty Fuel Economy Mode Switch, Fuel Economy Mode Switch harness is open or shorted, Fuel Economy Mode Switch 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: P159F GMC indicates Fuel Economy Mode Switch Circuit Low Voltage.
Common causes: Common causes include Faulty Fuel Economy Mode Switch, Fuel Economy Mode Switch harness is open or shorted, Fuel Economy Mode Switch 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 5,182

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 Jan 02, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P159F GMC Description

The Engine Control Module (ECM) supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the S87 fuel economy mode switch. The 5 V reference voltage causes current to flow through a series of resistors in the switch to the switch ground circuit. The ECM monitors the reference voltage through a discrete fuel economy mode switch signal circuit. When the switch button is momentarily pressed, the switch contacts allow the 5 V reference voltage to by-pass one of the resistors. The ECM detects the resulting voltage drop as a fuel economy mode request and sends a GMLAN message to the Transmission Control Module (TCM) indicating the request. When the TCM receives the request, throttle progressions and transmission shift points are modified to optimize fuel efficiency. The Instrument Panel Cluster (IPC) also receives the fuel economy mode request message from the ECM and illuminates the fuel economy mode indicator lamp. The fuel economy mode switch must be pressed for between 0.094-1.5 s to activate the fuel economy mode.

OBDII Code P159F GMC - Fuel Economy Mode Switch Circuit Low Voltage - AutoCodes.com — P159F GMC Code - Fuel Economy Mode Switch Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P159F GMC?

Faulty Fuel Economy Mode Switch
Fuel Economy Mode Switch harness is open or shorted
Fuel Economy Mode Switch circuit poor electrical connection

How to Fix the DTC P159F 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 P159F 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 P159F GMC code?

Need more information on how to fix the P159F GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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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 P159F GMC Code

1. What are the common symptoms of OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

The common symptoms of this code may include poor fuel economy, rough idle, and issues with the vehicle's performance.

2. What are the possible causes of OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

Possible causes of this code include a faulty fuel economy mode switch, damaged wiring or connectors in the circuit, or a problem with the vehicle's powertrain control module (PCM).

3. How can I diagnose OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

Diagnosing this code typically involves using a scan tool to read the code, checking the fuel economy mode switch for proper operation, inspecting the wiring and connectors for damage, and testing the PCM to ensure it is functioning correctly.

4. Can I drive my vehicle with OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

It is generally not recommended to drive your vehicle with this code present, as it can impact fuel efficiency and overall performance. It's best to address the issue promptly.

5. How can I repair OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

Repairing this code may involve replacing the fuel economy mode switch, repairing any damaged wiring or connectors, or reprogramming the PCM to resolve the issue.

6. Is OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage a serious issue?

While this code may not cause immediate harm to your vehicle, it can lead to decreased fuel efficiency and performance over time if left unresolved.

7. Can a DIY enthusiast fix OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

Depending on your level of expertise, you may be able to diagnose and repair this code yourself by following proper diagnostic procedures and using the necessary tools.

8. How much does it cost to fix OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage?

The cost of fixing this code can vary depending on the underlying cause and whether you choose to repair it yourself or seek professional help. Costs may include parts and labor.

9. Will OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage cause my check engine light to illuminate?

Yes, this code will typically trigger the check engine light to illuminate on your vehicle's dashboard, indicating a potential issue that needs attention.

10. How can I prevent OBDII code P159F (GMC) Fuel Economy Mode Switch Circuit Low Voltage from occurring in the future?

To prevent this code from recurring, it's essential to regularly maintain your vehicle, address any issues promptly, and follow recommended maintenance schedules provided by the manufacturer.