In part 1 of this instalment, we looked at some of the most common powertrain OBD II trouble codes. Here, we’re going to continue with five more of the most common codes, what they mean, and what you can do about them.
Let’s get started.
Recap: Diagnostic Trouble Code Groups
Before we begin, let's get a quick refresher on a few things. As you might know, OBD II trouble codes consist of 5 characters, and the first is an alphabet, representing the specific subsystem affected by the error.
So, while we are looking at OBD II trouble codes that start with P (representing Powertrain issues), you may want to know that the other codes are:
- B for body issues
- C for chassis issues, and
- U for undefined issues or network communication problems.
Why Do Similar Problems Have Multiple Trouble Codes?
Here’s another critical thing to remember about OBD II trouble codes: plenty of those codes tend to overlap. That is, you’ll find many different codes pointing to the same problem.
Well, for starters, OBD II trouble codes aren’t 100% accurate. That means you could get different codes that are almost similar, all trying to point you to the same root cause.
While they may point to the same problem, the differing codes may refer to specific parts affected.
So, without further ado, let’s look at another handful of the most common powertrain (P) OBD II codes, what they mean, and what you can do about them.
Common Powertrain OBD2 Codes and How to Fix Them
OBD2 DTC P0456
Affected part: This code is related to the car’s evaporative emission control (EVAP) system. More precisely, the code indicates there’s a small leak in that system.
What’s likely happening: When it comes to error codes indicating an EVAP leak, it’s important to remember that a ‘leak’ can mean several things. For instance, it could be something as simple as a loose or damaged gas cap, which isn’t too much of a big deal.
However, don’t take it too lightly, either. It could also be a severe issue like a leaking or disconnected EVAP hose, faulty purge volume control valve, a faulty canister vent control valve, a charcoal canister leak, or even a leaking fuel tank.
In simpler terms, while it might be just a problem with the fuel cap, you’ll still want to get this problem diagnosed properly.
Symptoms: This code will often be accompanied by an illuminated check engine light, unusually excessive fuel consumption or emissions, and the smell of fuel.
How to fix the problem: For this code, you can start by checking on your gas cap. Tighten the cap or replace it if necessary and see if the code persists. If it does, take it to your mechanic for a more thorough check.
OBD2 DTC P0128
Affected part: This code affects your engine temperature, indicating that your engine isn't getting hot enough as fast as it should. Now, that might not sound like a big deal at first. But remember that your engine (and all the fluids it relies on) have an optimal operating temperature that it must maintain.
So, even though the engine runs, and the vehicle is mobile, this problem will make it run a lot less efficiently.
What’s likely happening: The most likely reason behind this is that the thermostat is stuck open, that is, the engine is cooling down too much. Besides that, it also suggests an absent thermostat or a faulty coolant temperature sensor.
Sometimes, all the components are present and working correctly. However, faulty wiring in the coolant temperature circuit could prevent them from working as they should.
Symptoms: This is one of many problems that can trigger your Check Engine Light to turn on. Besides that, you might notice that your idling RPM is higher than usual and that your car’s fuel economy is less than usual.
Last but not least, the temperature gauge might also be lower than you’d generally expect it to be.
How to fix the problem: This problem will require troubleshooting the engine’s thermostat to be sure of the problem. That will most likely solve the problem. However, you’ll also want to be thorough by inspecting the coolant temperature sensor and the system’s wiring as well.
OBD2 DTC P0306 (related to P0304 and P0305)
Affected part: This code and several of the ones before it (P0305, P0304, etc.) point to a misfire in the engine. The number 6 at the end of the code tells you that the misfire occurred in the 6th cylinder of your engine.
What’s likely happening: Like any other misfire, this is likely happening because your spark plugs (the one for the 6th cylinder, of course) is faulty or worn out. Besides that, the wires or coils for that spark plug might be problematic as well.
Assuming you’ve ruled out those two most likely causes, you can then consider that there might be a problem with the engine distributor.
Symptoms: As far as symptoms go, you’re looking for the typical signs associated with engine misfiring. For starters, the Check Engine light would be turned on or flashing. Besides that, you’ll notice a lack of power from your engine, or that it’s running rough with lots of shaking. That’ll be especially true when you try to accelerate and notice your car jerking or hesitating.
Of course, misfiring means that the fuel in your engine isn’t getting burned correctly. That means your nose will likely pick up fuel smell coming from your exhaust when you step outside your car.
How to fix the problem: This is an easy fix. First, check the spark plug for your engine's 6th cylinder and replace it if necessary. If you'd like to be more thorough, check the wires, coils, distributor, and your other spark plugs while you're there.
Sure, those other components might not be causing you any problems right now. But in the spirit of 'preventive maintenance', if one spark plug gives you problems, you can bet that the others will follow suit soon enough. So, you might as well catch the issue before it triggers any other trouble codes.
To learn more about OBD II codes and other issues affecting car owners like yourself, stay tuned to the blog at CarpartAU. There, you’ll discover plenty of tips and tricks you can use to keep your car running better for longer.
By Ray Hasbollah