AutoCodes – GMC – P0990 2018 GMC Sierra

P0990 2018 GMC Sierra Code - Transmission Fluid Pressure Switch 5 Circuit High Voltage

Quick Answer

The Transmission Fluid Pressure (TFP) switch 5 is part of the Transmission Control Solenoid Valve Assembly, which has no serviceable parts. Common causes include Low transmission fluid level, Dirty transmission fluid, Faulty Transmission Control Solenoid Valve Assembly. 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: P0990 2018 GMC Sierra indicates Transmission Fluid Pressure Switch 5 Circuit High Voltage.
Common causes: Common causes include Low transmission fluid level, Dirty transmission fluid, Faulty Transmission Control Solenoid Valve Assembly.
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 777

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 25, 2024

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0990 2018 GMC Sierra Description

The Transmission Fluid Pressure (TFP) switch 5 is part of the Transmission Control Solenoid Valve Assembly, which has no serviceable parts. The Transmission Control Module (TCM) supplies a signal circuit to the TFP switch 5. The TFP switch 5 has an internal case ground. TFP switch 5 is normally closed or LOW. When oil pressure is present at the TFP switch 5, the switch is open or HIGH. The normally high-pressure control (PC) solenoid 3 controls pressure to the R1/4-5-6 clutch regular valve. The TCM monitors the TFP switch 5 signal circuit to determine the position of the R1/4-5-6 clutch regulator valve. When the low and reverse clutch and 4-5-6 clutch are commanded OFF, pressure is present on the TFP switch 5. When the low and reverse clutch or the 4-5-6 clutch is commanded ON, the R1/4-5-6 clutch regulator valve moves, and pressure to the TFP switch 5 is exhausted through the R1/4-5-6 clutch regulator valve. The Diagnostic Trouble Code (DTC) will be set when the TCM detects that the TFP switch 5 signal voltage remains HIGH after the 4-5-6 clutch transitions from a LOW pressure state to a HIGH pressure state. The TCM counts each incident. The DTC sets when 15 counts are accumulated.

OBDII Code P0990 2018 GMC Sierra - Transmission Fluid Pressure Switch 5 Circuit High Voltage - AutoCodes.com — P0990 2018 GMC Sierra Code - Transmission Fluid Pressure Switch 5 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0990 2018 GMC Sierra?

Low transmission fluid level
Dirty transmission fluid
Faulty Transmission Control Solenoid Valve Assembly
Transmission Control Solenoid Valve Assembly harness is open or shorted
Transmission Control Solenoid Valve Assembly circuit poor electrical connection

How to Fix the DTC P0990 2018 GMC Sierra?

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 P0990 2018 GMC Sierra 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 P0990 2018 GMC Sierra code?

Need more information on how to fix the P0990 2018 GMC Sierra 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 P0990 2018 GMC Sierra Code

1. What does the OBDII code P0990 mean on a 2018 GMC Sierra?

P0990 indicates a high voltage issue in the Transmission Fluid Pressure (TFP) Switch 5 Circuit, which monitors transmission fluid pressure to help manage shifting.

2. What are the common symptoms of the P0990 code in a 2018 GMC Sierra?

Symptoms may include harsh or erratic shifting, failure to shift gears, transmission stuck in one gear, or the check engine light illuminating.

3. What are the potential causes of a P0990 code in a GMC Sierra?

Possible causes include a faulty TFP switch, damaged or corroded wiring in the circuit, a malfunctioning transmission control module (TCM), or low transmission fluid.

4. Can low transmission fluid cause a P0990 code?

Yes, low or contaminated transmission fluid can cause inaccurate pressure readings, leading to the P0990 code.

5. How is the P0990 code diagnosed?

A mechanic will typically use a scan tool to verify the code, inspect the wiring and connectors for damage or corrosion, check the TFP switch, and test the transmission fluid level and condition.

6. Is it safe to drive with a P0990 code on a GMC Sierra?

Driving with a P0990 code is not recommended, as it can cause further damage to the transmission and lead to unsafe driving conditions.

7. How much does it cost to fix a P0990 code on a 2018 GMC Sierra?

Repair costs vary depending on the cause, but replacing the TFP switch typically costs between $150 and $400, including parts and labor.

8. Can I fix the P0990 code on my GMC Sierra myself?

If you have experience with automotive repairs, you can inspect and replace damaged wiring or the TFP switch. However, diagnosing the issue accurately may require professional tools and expertise.

9. What happens if the P0990 code is ignored?

Ignoring the P0990 code can lead to worsening transmission problems, increased repair costs, and potential transmission failure.

10. Does clearing the P0990 code solve the issue?

Clearing the code with a scan tool may turn off the check engine light temporarily, but the underlying issue must be repaired to prevent the code from returning.