P1186 – Fuel Pressure Monitoring-Minimum Pressure at Engine Speed Too Low (Hyundai)

By Reinier (Contact Me)
Last Updated 2022-02-07
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1186

Table of Contents

1. What Does Code P1186 Mean?
2. Where is the P1186 sensor located?
3. What are the common causes of code P1186?
4. What are the symptoms of code P1186?
5. Get Help with P1186

What Does Code P1186 Mean?

OBD II fault code P1186 is a manufacturer-specific trouble code that is defined by carmaker Hyundai as, “Fuel Pressure Monitoring-Minimum Pressure at Engine Speed Too Low”, and is set when the PCM (Powertrain Control Module) in Hyundai vehicles detects one or more of the following three conditions-

1) The actual fuel pressure in the fuel rail is lower than the desired fuel pressure by a predefined value (which depends on the engine) for longer than one second, given the current engine speed and load. Note that in the context of this code, the volume of fuel supplied to the fuel rail is a function of the fuel pressure. Nonetheless, typical deviations between the actual and desired fuel rail pressure that will set code P1186 on Hyundai vehicles fall in a range of between 100 bars and 500 bars.

2) The volume of fuel passed back to the fuel tank through the fuel pressure regulator exceeds a predefined value, which value depends on the specific engine.

3) The presence of a short circuit, or the presence of abnormal and/or unexpected electrical values in the control and/or signal circuit(s) of the fuel pressure sensor.

Unlike most other common rail diesel injection systems, the fuel system on Hyundai vehicles uses a single component to control and monitor both the input pressure from the high-pressure injection pump and the volume of fuel that is passed back to the fuel tank as a means to relieve excess pressure in the fuel rail. The actual pressure in the fuel rail is monitored by a dedicated fuel pressure sensor in the fuel rail.

During normal operation of the engine, the PCM calculates the fuel demand based on the engine speed and load, which information it uses to control the volume of fuel that enters the fuel rail on the one hand and to control the actual pressure in the fuel rail by opening or closing the fuel pressure regulator valve, on the other.

Thus, in a fully functional injection system, the PCM can control and maintain the actual pressure within an exceedingly narrow range but as a kind of “double-check”, the PCM also monitors the volume of excess fuel that is passed back to the fuel tank. Therefore, as a practical matter, the PCM compares the input fuel pressure (from the injection pump) with the calculated demand for fuel at any given point in the engines’ operating range as a first step to maintaining an appropriate fuel pressure value.

The second step in this process involves comparing the actual fuel pressure with the desired fuel pressure, and this value is then compared with the actual pressure in the fuel rail as reported by the fuel pressure sensor. As a third step, the PCM compares the actual pressure in the fuel rail with the flow rate of the fuel returning to the fuel tank.

Provided all the components in the injection system work as designed, the PCM can match the volume and pressure of fuel (that is available to the injectors) to the calculated demand for fuel at any engine speed and load exactly, which increases the overall engine efficiency and reduces both fuel consumption and exhaust emissions, at the same time.

However, while this overly complicated injection system works well when it works as designed, the overall implementation of the control system is somewhat prone to common faults and malfunctions of several components. When the PCM detects one or more such faults or defects, it will recognize that it cannot control the fuel injection system effectively, and will set code P1186, and illuminate a warning light as a result.

Note, also, that in the majority of instances of code P1186 on Hyundai vehicles, the PCM will either initiate a limp mode, or limit the engine speed to about 3000RPM both as a safety precaution, and to prevent damage to the engine and/or injection equipment.

Where is the P1186 sensor located?

This image shows the location (circled) of the fuel pressure regulator valve on a 2016 Hyundai Elantra application. Note though that, while the valve is easily accessible on this vehicle, it may be necessary to remove or disassemble unrelated engine parts or components to gain easy access to the fuel pressure regulator on many other Hyundai models.

Also, note that while failures of the fuel pressure regulator valve is a relatively common cause of code P1186 on Hyundai vehicles, this component should only be condemned after checks for blocked fuel filters, defective lift pumps, and/or defective injectors have ruled out these issues as the cause of the low fuel pressure condition.

What are the common causes of code P1186?

The most common causes of code P1186 on Hyundai vehicles are largely the same across all applications and could include one or more of the following-

• Defective or malfunctioning fuel pressure regulator valve (Stuck in an open position)
• Defective or faulty fuel pressure sensor
• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors anywhere in the fuel system
• Dirty, clogged, or defective fuel lift pump
• Dirt, clogged, or damaged fuel filter
• Dirty or contaminated fuel that can clog filters and/or fuel lines
• One or more defective or damaged fuel injectors (Stuck in the open position)
• Defective or damaged high-pressure injection pump (This is common in areas where bad fuel quality is the norm rather than the exception)
• Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced or reprogrammed

What are the symptoms of code P1186?

The common symptoms of code P1186 on Hyundai vehicles are the same across all applications and could include one or more of the following-

• Stored trouble code and an illuminated warning light that may or may not be flashing red
• Depending on the exact nature of the problem, multiple additional trouble codes may be present along with P1186
• The vehicle may be in a limp mode, or the engine speed may be severely restricted
• The engine may stall or shut off unexpectedly at any engine speed, but note that in some cases the engine may restart immediately, only to again stall or shut off again almost immediately
• In some cases, the engine may stall or shut off intermittently; sometimes with several days or even weeks between episodes
• Depending on the nature of the problem, the engine may only restart after several hours
• In some cases, and depending on the nature of the problem, the engine may only start after prolonged cranking
• In rare cases, the engine may not start at all even though it may crank normally
• The engine may lose progressively more power over several days (or weeks, in some cases)before symptoms like repeated stalling begin to appear
• The vehicle may require repeated fuel filter replacements, which is indicative of contaminated fuel

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