How To Reset Check Engine Light on Peterbilt 389

How To Reset Check Engine Light on Peterbilt 389

It was the evening of a sunny day. When I noticed the check engine light on my truck, I was parking it in the garage. Suddenly, I panicked. Then I thought, “Why is this? How to reset check engine light on Peterbilt 389?

To reset the check engine light on Peterbilt 389, with the key in the “Run” position but the engine off, quickly switch it to the “Off” position. Check for trouble codes on the diagnostics panel and address any issues. Do this five times within the correct time range. 

I did thorough research to find the reasons for the check engine light and how to reset check engine light on Peterbilt 389. After trying different methods, I was able to select the correct one. In this article, I will explain the reasons for the check engine light on the Peterbilt and how I successfully reset the check engine light on my Peterbilt 389 truck.

Peterbilt 389

What Is the Engine Light on Trucks?

In the 1980s, the check engine light became a common safety signal. In essence, it’s a prompt and practical way for your truck to alert you of a problem under the hood. The onboard diagnostic (OBD) system in your truck includes the check engine light. The OBD, which houses numerous electronic sensors, is like the brain of your truck. These sensors keep track of everything, including the amount of fuel burned and the flow of oxygen via your engine.

Why Does the Check Engine Light Come On?

When the OBD notices a problem, it tries to fix it on its own. It notifies you if those self-repairs are unsuccessful by turning on a dashboard indicator.

Peterbilt 389 check engine light
Check Engine Light IssueSuitable Actions
Faulty Oxygen SensorReplace the faulty oxygen sensor with a new one.
Loose or Damaged Gas CapCheck the gas cap for proper tightening and replace it if damaged.
Malfunctioning Mass Airflow SensorClean the mass airflow sensor.
Issues with the Catalytic ConverterRepair the catalytic converter
Faulty Spark Plugs or Ignition CoilsReplace the spark plugs and worn-out ignition coils
Problems with the EGR SystemClean and repair the EGR system components to restore proper functionality.
Faulty Engine Control Module (ECM) or SensorDiagnose the ECM or faulty sensor and repair or replace it accordingly. Repair the ECM Replace any malfunctioning sensors
Issues with the Fuel Injection SystemRepair the components to ensure proper fuel delivery.
Malfunctioning Evaporative Emission Control SystemFirst, try repairing Sometimes you may have to replace them
Low Oil Pressure or Oil LeaksInspect the engine for oil leaks and repair any leaks. You need to bleed the system if the oil pressure is low.
Problems with the TransmissionDiagnose and repair transmission-related components to resolve issues.
Engine Misfire or Cylinder MisfireReplace components such as spark plugs, ignition coils, or fuel injectors.
Sensor or Wiring Harness MalfunctionCheck the sensor or wiring harness for faults Repair any issues. Replace the faulty components.
Low Battery Voltage or Charging System IssuesInspect the battery and charging system for problems Repair or replace components as needed
Problems with the Exhaust System or MufflerInspect the exhaust system and muffler for damage Repair or replace components as necessary

How To Reset Check Engine Light on Peterbilt 389?

So, how to reset check engine light on Peterbilt 389? The check engine light on my Peterbilt had come on due to a damaged gas cap. Before starting the reset process, I replaced my gas cap. This is how I reset check engine light of my truck.

I ensured that the key was in the “Run” position, but the engine was off.

First, I turned the key to the run position without starting the engine and then turned it to the off position.

Then I turned the key to the “off” position.

I quickly turned the key back to the “Run” position five or six times within five seconds. It means I turned the dashboard lights on and off very rapidly. I think you’ve got it.

If the check engine light didn’t go off immediately, I repeated steps 2 and 3 to ensure I did the procedure correctly.

Then I looked to see if there were any trouble codes on the diagnostic panels. Yes. It was P0455. So, I searched Google to find the meaning of the code. It was for the loose gas cap, as I mentioned above.

Then I started the engine and check engine light was gone! Reset was successful!

Note: Sometimes there will be no fault code in your Peterbilt. The check engine light may come on due to an incorrect signal sent by a sensor.If you see a fault code in your truck, you need to fix the underlying issue before resetting the check engine light. If not, the engine light will illuminate again after a few riding cycles.


What is the price of a brand new Peterbilt 389?

A brand-new Peterbilt 389 will cost over $250,000. Tanker models will cost at least $400,000 more than average.

Does the Peterbilt 839 check engine light of reset automatically?

After the issue that triggered the check engine light has been fixed, it usually turns off automatically, after 10 to 20 cycles.

What is the difference between engine light and check engine light?

The engine light’s job is to inform us when it is time for regular maintenance. On the other hand, the check engine light comes on when there is a problem in the transmission or in the engine.

Does oil light mean low oil in Peterbilt?

An oil light means the vehicle’s oil pressure is low. You may be low on oil, your oil is unclean, or you may have an oil leak if your oil pressure drops for any of these reasons.


Now you know how to reset check engine light on Peterbilt 389. It is a very simple process that can be done yourself within minutes. Thanks for reading. Have a nice day!

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