What Codes Will This Page Cover?
Here are the codes you’ll learn about on this page:
- P1391 Diagnostic Code – Glow Plug Circuit Low Input (Bank #1)
- P1392 Diagnostic Code – Glow Plug Circuit High Input (Bank #1)
- P1393 Diagnostic Code – Glow Plug Circuit Low Input (Bank #2)
- P1394 Diagnostic Code – Glow Plug Circuit High Input (Bank #2)
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What Is the P1391 Code?
Symptoms
Causes
Seriousness
Can I Still Drive?
Diagnose
Difficulty of Inspecting
Get Additional Help
The P1391, P1392, P1393, and P1394 codes refer to issues with your glow plug circuit. Glow plugs are diesel-specific resistors which heat up when the diesel engine applies a current to them. That heat is then transferred to the air/fuel mixture, which helps your air/fuel mixture combust effectively, especially when the engine is cold. Once the engine warms up, these plugs may keep functioning to improve air/fuel combustion. These codes indicate issues with the voltage in the glow plug circuit.
More About the P1391, P1392, P1393, and P1394 Codes
Although these codes are very similar, they’re not identical. Here’s how the P1391, P1392, P1393, and P1394 codes differ:
- P1391: Glow Plug Circuit Low Input Bank 1 – A problem with a low input voltage for your bank 1 glow plug
- P1392: Glow Plug Circuit High Input Bank 1 – A problem with high input voltage for your bank 1 glow plug
- P1393: Glow Plug Circuit Low Input Bank 2 – A problem with low input voltage for your bank 2 glow plug
- P1394: Glow Plug Circuit High Input Bank 2 – A problem with high input voltage for your bank 2 glow plug
The specific OBD code that you’re experiencing will give you more insight into which bank you should look at, as well as whether the problem is a low voltage or a high voltage. Additionally, remember that not all car manufacturers will use these definitions, so it’s important to look at the description for the car code as well before testing your glow plug circuit.
What Are the Symptoms of a P1391 Code?
Depending on exactly the problem and the extent of the problem, the symptoms of codes P1391, P1392, P1393, and P1394 can vary. You may see issues with starting your vehicle, including a no-start condition with a cold engine, idling problems with the engine, especially in the first few minutes of function, extended cranking times with a cold engine, and other idling and starting problems. You’ll usually see the check engine light even without any of these problems.
What Are Some Causes of a P1391 Code?
For the codes that have to do with low voltage, P1391 and P1393, it’s common for the problem to lie with the connectors, wiring, circuits, and battery voltage. Note that if your overall battery voltage is low, you’ll often see other warning codes that relate to your battery overall. When it comes to the codes that have to do with high voltage, you may be more likely to see issues with the glow plug relay or timer, as well as issues with the engine coolant, oil temperature, or intake air temperature sensors.
How Serious Is the P1391 Code?
The seriousness of this problem often has to do with the actual problem causing these codes, as well as the symptoms present. For example, if your vehicle has a no-start condition, the problem is obviously very serious, and you’ll need to deal with it seriously. However, it’s also important to remember that what seems like a non-serious problem can quickly spiral out of control. Treat the problem as though it is serious and invest in a fix early.
Can I Still Drive with a P1391 Code?
If your vehicle is unable to idle properly or completely unable to start, then you simply won’t be able to drive at all. However, the P1391, P1392, P1393, and P1394 codes can also show up in a completely drivable car. If you see issues with drivability, then contact your local repair shop to see whether you need a tow truck to bring your vehicle in or whether you’re safe to drive to your local shop.
How Easy Is It to Diagnose a P1391 Code?
The diagnostic process for these codes requires a number of steps and a lot of hard work. For many people, diagnosing the P1391, P1392, P1393, and P1394 codes is more than is possible for a casual DIYer. If you are a DIYer, then you should only attempt diagnosis or repair of any glow plug codes if you have a manual and technical information available, as false diagnostic procedures can cause problems to your vehicle’s entire electrical system.
How Difficult Is It to Inspect a P1391 Code?
To inspect the P1391, P1392, P1393, and P1394 codes, you’ll need to check a number of different areas in the vehicle, and you’ll also need to know the way that a well-functioning vehicle of your make and model looks. The significant amount of knowledge necessary can make it difficult for individuals who aren’t professionals to inspect and diagnose these codes.
Need Additional Help with Your P1391 Code?
The P1391, P1392, P1393, and P1394 codes can all have a marked impact on your vehicle’s proper functioning, and if you need more help with them, you might want to talk to an expert rather than trying to piece it together on your own.
For more help from an expert, use Kelley to find a repair shop in your area. This is an effective way to fix the problems you’re seeing, no matter what they are or why they’re showing up.
Additionally, the first step to DIY vehicle fixes is understanding error codes. The KBB OBD-II database will help you understand more types of error codes overall.
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