AutoCodes – Pontiac – P0128 Pontiac

P0128 Pontiac Code - Engine Coolant Temperature Below Thermostat Regulating Temperature

Quick Answer

The Engine Control Module (ECM) monitors the temperature of the engine coolant for engine control and as enabling criteria for some diagnostics. Common causes include Leaking or stuck open thermostat, Low engine coolant level, Insufficient warm up time. 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: P0128 Pontiac indicates Engine Coolant Temperature Below Thermostat Regulating Temperature.
Common causes: Common causes include Leaking or stuck open thermostat, Low engine coolant level, Insufficient warm up time.
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 41,871

How popular is this code, among other codes? Medium

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Apr 20, 2023

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
FAQs
Comments
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Code P0128 Pontiac Description

The Engine Control Module (ECM) monitors the temperature of the engine coolant for engine control and as enabling criteria for some diagnostics. The amount of heat an engine generates is proportional to the amount of air that enters the engine. The ECM monitors this amount of air to calculate a theoretical Engine Coolant Temperature (ECT). The ECM uses the calculated temperature to determine if the engine has warmed up to the thermostat regulating temperature. Suppose the measured actual coolant temperature does not increase typically or does not reach the thermostat regulating temperature. In that case, diagnostics that use the ECT as enabling criteria, may not run when expected. If the measured engine coolant temperature fails to reach the thermostat regulating temperature, before a predetermined amount of air has entered the engine, this Diagnostic Trouble Code (DTC) sets.

OBDII Code P0128 Pontiac - Engine Coolant Temperature Below Thermostat Regulating Temperature - AutoCodes.com — P0128 Pontiac Code - Engine Coolant Temperature Below Thermostat Regulating Temperature

What does this mean?

What are the Possible Causes of the DTC P0128 Pontiac?

Leaking or stuck open thermostat
Low engine coolant level
Insufficient warm up time
Faulty engine coolant temperature sensor
Engine coolant temperature sensor harness is open or shorted
Engine coolant temperature sensor circuit poor electrical connection

How to Fix the DTC P0128 Pontiac?

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

If the cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.

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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0128 Pontiac 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.

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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 P0128 Pontiac Code

1. What are the common symptoms of OBDII code P0128 in a Pontiac?

The common symptoms of OBDII code P0128 in a Pontiac include the engine running colder than normal, decreased fuel efficiency, and the check engine light illuminating on the dashboard.

2. What are the possible causes of OBDII code P0128 in a Pontiac?

Possible causes of OBDII code P0128 in a Pontiac include a faulty thermostat, a malfunctioning engine coolant temperature sensor, low coolant levels, or a problem with the cooling system.

3. How can I diagnose OBDII code P0128 in my Pontiac?

To diagnose OBDII code P0128 in your Pontiac, you can use an OBDII scanner to read the code and check the engine coolant temperature sensor readings. Additionally, you can visually inspect the thermostat and cooling system for any signs of damage.

4. Can I still drive my Pontiac with OBDII code P0128?

It is not recommended to drive your Pontiac with OBDII code P0128 for an extended period of time, as it can lead to engine overheating and potential damage. It is best to address the issue promptly to prevent further problems.

5. How can I repair OBDII code P0128 in my Pontiac?

To repair OBDII code P0128 in your Pontiac, you may need to replace the thermostat, engine coolant temperature sensor, or address any issues with the cooling system. It is recommended to consult a professional mechanic for proper diagnosis and repair.

6. Is it safe to reset the OBDII code P0128 in my Pontiac without fixing the underlying issue?

Resetting the OBDII code P0128 in your Pontiac without fixing the underlying issue is not recommended, as the problem may persist and potentially lead to more severe issues in the future. It is best to address the root cause of the code to ensure proper functioning of your vehicle.

7. How often does OBDII code P0128 occur in Pontiac vehicles?

OBDII code P0128 can occur in Pontiac vehicles due to various factors such as age, mileage, and maintenance history. Regular coolant system checks and maintenance can help prevent this code from occurring.

8. Can a DIY enthusiast fix OBDII code P0128 in a Pontiac?

While some DIY enthusiasts may have the skills to diagnose and repair OBDII code P0128 in a Pontiac, it is recommended to seek professional help, especially if you are unsure about the root cause of the issue or lack experience working on automotive cooling systems.

9. Will OBDII code P0128 cause permanent damage to my Pontiac if left unresolved?

If left unresolved, OBDII code P0128 can potentially cause permanent damage to your Pontiac's engine due to overheating. It is crucial to address the issue promptly to prevent any long-term damage.

10. How much does it cost to fix OBDII code P0128 in a Pontiac?

The cost of fixing OBDII code P0128 in a Pontiac can vary depending on the underlying issue, parts needed for replacement, and labor costs. It is recommended to obtain quotes from different mechanics or repair shops to determine the total cost of repair.