What Is the P1399 Code?
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The P1399 code is a manufacturer-specific code and most often relates to Ford vehicles. The code’s definition is “Glow Plug Circuit High Side, High Input”, and it appears when the Powertrain Control Module (PCM) notices an atypical input voltage reading on the high side of the referenced glow plug control circuit. The high side of this system is the electronic circuit that incorporates switching mechanisms that work by controlling each glow plug separately.
Diesel engines have glow plugs and circuits that work by preheating the air and fuel mixture so that the engine can combust the mixture when cold. Essentially, the PCM works to deliver readings like the engine temperature to the glow plug control module. This module then determines the appropriate pulse width to manage each glow plug separately. The glow plug control module is also able to monitor battery voltage, as well as the charge pump and its supply voltages. It also monitors the condition of each high side switch and is able to manage the current flows from each glow plug. Once any irregularities occur in this process, the PCM triggers the P1399 code.
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What Are the Symptoms of a P1399 Code?
The first symptom to expect from a P1399 code is the check engine light illuminating on your dashboard to indicate an issue exists. As far as physical symptoms, you can expect to have trouble starting your engine over on a cold start. If the glow plug control module fails completely, then it’s highly likely that you won’t be able to start your engine at all in lower temperatures. In some cases, it’s possible that your tailpipe starts emitting white smoke when it does turn over.
What Are Some Causes of a P1399 Code?
The exact cause of the P1399 issue can vary from model to model, but you can usually expect short circuits to be at the root of the issue. Damaged wiring or corroded wiring connectors are also common causes across all vehicles. The glow plug control module is also known to trigger the P1399 code if the module is damaged or defective. The wiring leading to this module, as well as the PCM, can also cause the issue if they’re damaged. In rare cases, a faulty PCM can be at the root of this issue, but this is unlikely.
How Serious Is the P1399 Code?
A P1399 code can become severe if the issue leads to you not being able to start your engine at all in low temperatures. Once this happens, it’s tough to diagnose the issue without doing a complete inspection of the glow plug control circuit. If your engine continues to have trouble cranking over and you continue to ignore this issue, then it’s likely that you can cause damage to other engine components. Needless to say, you should take your vehicle to a certified service center as soon as possible to avoid further damage to your engine.
Can I Still Drive with a P1399 Code?
If your vehicle can crank over, then you may not notice any immediate driveability issues with your car. The problem lies in ignoring this issue if your engine is having difficulties turning over. Continuously putting your car under this strain could eventually lead to your engine not starting at all and white smoke starting to emit from your tailpipe. This is never a good sign with any issue; it means that you should have your car inspected by a qualified technician with previous experience working on glow plug circuit issues.
How Easy Is It to Diagnose a P1399 Code?
The first step in diagnosing the P1399 code issue is to pull and record all of the codes set by the PCM, as well as all available freeze frame data. In most scenarios, the sensors in the glow plug control circuit rely on readings from the oil temperature sensor and atmospheric pressure sensor. So, it’s important to assess how these sensors are working and if they are damaged or defective. A technician will then assess the glow plug control module and its related wires and connectors. They will establish the module ground as well as input circuits and make sure that the ground is stable and the right input voltage exists at the connector. Following this, the technician will begin to inspect the glow plugs individually and perform tests on them to see how well they’re working.
How Difficult Is It to Inspect a P1399 Code?
This inspection process with the P1399 code involves many tests and visual inspections. As such, qualified technicians with experience working on diesel motors are the best individuals to inspect this issue. Needless to say, technicians do not recommend that you DIY this process at home because it’s highly likely that you will misdiagnose the root of the issue. This can only lead to more repairs for your engine and further repair bills. Instead, a technician will assess the sensors associated with the glow plug control circuit and make the proper replacements. They will then look at the glow plug control module and test it before determining if they need to replace it. Finally, they will perform circuit tests on the individual glow plugs and make the necessary repairs or replace the glow plugs altogether if they are defective.
Need Additional Help with Your P1399 Code?
The P1399 issue isn’t a simple one and requires an experienced technician to properly inspect it. Hopefully, by following our guidelines, you’ll be able to spot the issue when it appears and take the proper steps to have it repaired. Doing so will ensure that your diesel engine continues to start without issues and is running in great condition.
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