P0191 Code (Symptoms, Causes, and How to Fix)
Is your car’s check engine light suddenly illuminated, and a diagnostic scan revealed a P0191 trouble code? You’re likely wondering what this means for your vehicle’s health and how it might impact your daily commute.
Don’t stress just yet. Keep reading to learn what a P0191 fault code really means, what caused it, whether it’s safe to keep driving, and how to properly resolve it in a step-by-step manner.
What Does Code P0191 Mean?
Diagnostic fault code P0191 corresponds to a perceived issue with the affected vehicle’s fuel rail pressure sensor circuit. As such, the vehicle’s powertrain control module (PCM) has determined feedback from the corresponding fuel rail pressure sensor to be erratic or irrational.
Simply put, this feedback does not mirror that which the PCM expects to see under current operating conditions.
To better understand this, you must first familiarize yourself with the general function of the fuel rail pressure sensor. This sensor provides valuable feedback to a vehicle’s PCM, regarding the available fuel pressure present at an engine’s fuel rail. This feedback is used to assist in regulating fuel injector output, thus preventing under/overfueling.
A number of fail-safe measures have been built into most modern PCMs. One such fail-safe centers around the PCM’s ability to determine if feedback provided by certain sensors is rational.
In the event that one or more data streams appear compromised, most PCMs are programmed to default to preset figures that allow engine operation to be sustained. However, performance generally suffers, due to a lack of accuracy in true operating conditions.
Related: Code P0087, Code P0193
Symptoms of Code P0191
Diagnostic fault code P0191 is often associated with a handful of secondary symptoms, a number of which can prove troubling to contend with. Recognizing these symptoms should be priority number one when attempting to discern the root cause of your vehicle’s issues.
Here are some of the most common symptoms you can expect:
- Illuminated check engine light
- Failure to start
- Intermittent engine stalling
- Reduced engine power
- Failed emissions testing
Causes of Code P0191
Diagnostic fault code P0191 can be caused by a host of underlying issues, at least a few of which often prove difficult to pinpoint. Nonetheless, familiarizing yourself with the potential causes of this fault can help you quickly rule out those that don’t apply.
- Faulty FRP Sensor
- One or more vacuum leaks
- FRP-related wiring issues
- Minimal fuel pressure at the rail
- Exceedingly high fuel pressure at rail
Is Code P0191 Serious?
Diagnostic fault code P0191 is generally considered to be rather serious in nature. Most manufacturers caution against driving with an active P0191 fault code, for a number of reasons.
The first of which centers around the possibility that a vehicle exhibiting this fault can stall without warning, under periods of high fuel demand.
Additionally, running any engine under lean conditions for an extended period of time can lead to unanticipated, yet significant internal damage. Alternatively, overly rich fueling can prove equally detrimental, leading to “washed-down” cylinder walls, and oil dilution. This, in turn, can lead to premature bearing and piston ring wear.
It’s important to find and fix the cause of the P0191 code quickly. This helps protect your engine from damage and prevents future driving problems. If you’re not comfortable doing the repairs yourself, take your car to a trusted mechanic as soon as you can.
How to Fix Code P0191
To help in pinpointing and repairing the root cause of a vehicle’s P0191 diagnostic fault code, follow these step-by-step troubleshooting instructions. It is also advisable to seek out factory-specific service literature for your particular make and model of vehicle before attempting any such repairs.
#1 – Check For Additional DTCs
Before getting overly involved in the diagnostic process, check for the presence of any additional fault codes. Any such codes that are retrieved should be thoroughly examined before proceeding so you’re not combining symptoms from unrelated issues.
#2 – Inspect FRP Sensor
First, begin by carefully inspecting the engine’s fuel rail pressure sensor for signs of damage or corrosion at its connector. Any such damage should be corrected before proceeding. This typically involves replacing the sensor.
Additionally, check for any corrosion within the FRP connector itself. Any corrosion that is evident should be thoroughly cleaned with an electrical contact cleaner and a nylon bristle brush.
#3 – Inspect FRP Circuit
Next, a full continuity check should be performed across all legs of the fuel rail pressure sensor circuit, with the use of a quality multimeter. Such tests should be conducted in accordance with factory-specific service literature for the model of the vehicle in question.
#4 – Compare Digital/Mechanical Data
If no other issues have been located to this point, pressure readings taken at the fuel rail with a mechanical gauge will need to be compared to those registered digitally via freeze-frame data. If such readings differ significantly, a faulty fuel rail pressure sensor is to be suspected.
#5 – Assess Pressure Discrepancies
If digital and mechanical fuel pressure readings correspond, you must determine if the pressures recorded fall outside of that specified by the vehicle’s manufacturer. If all checks are within range, further evaluation of the vehicle’s PCM will be required.
If these pressures fall outside of the range specified, further inspection of the fuel system itself will be necessitated.
#6 – Follow Further Testing Measures
Further testing along these lines should be conducted in strict accordance with that specified by the vehicle’s manufacturer. This will help prevent the misdiagnosis of components that are otherwise of a functioning nature, many of which can be quite expensive to replace.
If any of these troubleshooting steps are beyond you mechanical abilities, don’t risk making the problem worse. Instead, get your vehicle scheduled for a professional to diagnose and fix the issue.
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