The vehicle engine contains different sensors to ensure its efficient working. The fuel rail pressure (also known as a fuel pressure sensor) is one of the most important sensors. It is used to measure the fuel pressure in the fuel rails. The powertrain control module (PCM) uses the fuel pressure sensor data to control the fuel delivery to the engine. Whenever your PCM receives a wrong fuel rail pressure sensor signal, it triggers the P0191 code. This article mainly explains the P0191 code meaning, causes, and symptoms.
P0191 Code Definition
P0191 code stands for “Fuel Rail Pressure Sensor Circuit “A” Range/Performance.”
What Does the P0191 Code Mean?
The trouble code P0191 indicates that your powertrain control module is receiving inconsistent readings from the fuel rail pressure sensor.
A very low fuel supply can cause the engine to suffer performance issues, especially in high loads. On the other hand, if your engine consumes more fuel than usual, it will increase exhaust emissions and can damage the catalytic converter.
To prevent rich and lean fuel mixtures from affecting engine performance, your powertrain control module adjusts injector performance to deliver a precise amount of fuel to the engine combustion chamber.
In the case of the latest vehicles, the PCM relies on the fuel line pressure sensor to send a constant stream of accurate data.
The fuel rail pressure sensor is also known as a fuel pressure sensor. These sensors are most commonly used in diesel engines and some petrol engines. The fuel pressure sensor measures the fuel pressure in the fuel rails. The fuel rail pressure sensor is installed near the fuel rail center and is linked to the PCM.
When your PCM receives a fault signal from the sensor, it logs a P0191 code.
Causes of P0191 Code
- Bad fuel pressure sensor
- Bad fuel pressure regulator
- The problems with the fuel pressure sensor circuit
- Insufficient fuel
- Bad fuel pressure sensor connector
- Bad or loose connection
- Bad fuel pressure regulator
- Clogged fuel filter
- Bad fuel pump
- Damaged or corroded wiring
- Vacuum leaks
- PCM issues (such as software needs updating)
Symptoms of Code P0191
- Check Engine Light illumination
- Unpleasant smell in the exhaust emissions
- The engine may cut off when the vehicle stops
- Failed emissions test
- Poor engine performance
- Engine stalling
- PCM/ECM trigged the rich fuel trim code (P0172 Code: Fuel system too rich)
- Poor fuel economy
- PCM/ECM trigged a lean fuel trim code (such as P0171 Code: Fuel system too lean)
- No clear symptoms
How to diagnose the P0191 Code?
- Use an OBD-II scanner to inspect the presence of the P0191 code.
- Perform a test drive and records the live data to find whether the fuel pressure reading is normal or not.
- Inspect the sensor wiring for damage or corrosion
- Inspect the connectors for loose connection
- Use a fuel pressure tester to check the fuel pressure sensor or fuel pressure problem.
- If the fuel pressure is normal, use an oscilloscope to test the wiring and connector of the sensor.
- The sensor is most likely faulty if the actual fuel pressure is normal and the sensor’s circuitry is unimpaired.
Common P0191 Code Diagnosis Mistakes
- Inability to confirm the presence of the P0191 code.
- Clearing the code without first verifying the problem
- Not performing a visual test or replacing parts unnecessarily
- Failing to clear the PCM codes after fixing the codes
- Changing the fuel pressure sensor without inspecting the wiring and connections.
- Not inspecting the fuel rail system for a leak before continuing with diagnostics.
What Repairs Can Fix the P0191 Code?
- Replacing the bad fuel pump
- Changing the bad fuel pressure sensor
- Check the vacuum hose for holes, tears, or damage in the hose material
- Fixing the vacuum leak in the engine
- Replacing or repairing the bad fuel pressure regulator
- Inspecting the fuel injector. If it is clogged, then clean it; otherwise, replace it.
- Repairing the damaged, shorted, or frayed wiring to the sensor
- Repairing or replacing the faulty or loose connectors to the fuel pressure sensor
- Reprograming the PCM
Repair Cost of P0191 Code
The repair cost of the P0191 code varies according to labor cost, the vehicle model, and your area. To fix this code, you may need one or more of the following repairs:
| Parts | Cost |
|---|---|
| Vacuum leak repair | $70 to $380 |
| Fuel pump replacement | $250 to $1,090 |
| PCM replacement | $240 to $3,000 |
| Fuel Pressure Sensor replacement | $240 to $420 |
FAQ Section
How serious is the P0191 code?
The code P0191 is considered a serious code. This code may cause multiple drivability problems. Driving with this code may cause the vehicle to stall or hesitate while driving. Driving with this code may lead to poor fuel economy, which can be expensive. Therefore, you shouldn’t ignore this code and diagnose and fix it as soon as possible.
What happens if I unplug the fuel rail pressure sensor?
If the fuel pressure sensor is not connected, the pump will run at a fixed speed, potentially reducing engine power and throttle.
What are the Causes of the P0191 code?
- Bad fuel pressure sensor
- Bad fuel pressure regulator
- The problems with the fuel pressure sensor circuit
- Insufficient fuel
- Bad fuel pressure sensor connector
- Bad or loose connection
- Bad fuel pressure regulator
- Clogged fuel filter
- Bad fuel pump
- Damaged or corroded wiring
- Vacuum leaks
- PCM issues (such as software needs updating)
Does a faulty fuel pump throw a code?
A bad fuel pressure sensor or a bad fuel pump triggers the P0087 or P0191 code and check engine light illumination. However, your check engine light may start illuminating due to many other reasons.
How do you fix the fuel rail system pressure too low?
The following repairs may help you to fix the too-low pressure in your fuel rails:
- Replacing the bad fuel filters
- Replacing the fuel pressure sensor
- Replacing or cleaning the fuel pump
- Fixing the vacuum leaks
- Replacing the PCM
- Check the fuel level and add more fuel if needed
Where is the fuel rail pressure sensor located?
The fuel rail pressure sensor is located near the fuel rail center and is linked to the powertrain control module (PCM).
What happens when the fuel pump goes out while driving?
A faulty fuel pump can overheat and can’t efficiently supply fuel to the engine, which causes the engine to overheat and stall while driving on the road. In such conditions, the vehicle can be restarted after overheating and shutting down, but only 30 minutes later. This condition is a sign of fuel pump damage.
Can I drive without a fuel pressure sensor?
Yes, you can drive without a fuel pressure sensor, but you may face many drivability problems. If the pressure switch fails, the PCM will have no feedback to regulate fuel pressure and may trigger into failure mode. Failure mode may lead the engine to run erratically and the transmission to shift abruptly, causing the problem you are having.
Can I drive with the P0191 Code?
Yes, you can drive with the P0191 code. However, driving with this code may lead to various drivability issues, such as poor engine performance, poor fuel economy, or engine stalling. You shouldn’t drive your vehicle with this code for a long time because it may badly damage your catalytic converter.