P0194 code definition
Fuel rail pressure sensor ‘A’ circuit intermittent/erratic
What the P0194 code means
The P0194 code is specific to diesel engines and will not likely be used in reference to gas engines. The test associated with this code is designed to monitor the condition of the fuel rail pressure (FRP) sensor. This consists of all the wires that are part of the FRP sensor circuit which allow the computer to monitor fuel rail pressure. A diesel motor utilizes this information to properly meter the air/fuel ratio.
What causes the P0194 code?
This code is set when the powertrain control module (PCM) observes inconsistent signals in the FRP circuit. The PCM expects only a few patterns out of this circuit. When it detects out of the ordinary patterns, this code will be set. Components that can cause this code include:
- Fuel rail pressure sensor
- Fuel pressure regulator
- Harness issues, usually where the harness enters the valve cover
- A faulty PCM
What are the symptoms of the P0194 code?
Symptoms are varied and are dependent on the fuel injection system the manufacturer chooses to use. These symptoms include:
- Check Engine Light
- Hard cold start
How does a mechanic diagnose the P0194 code?
A technician begins by connecting a scanner to the Data Link Connector (DLC), also known as the OBD-II scanner, to retrieve any codes and freeze frame data.
Once that information is stored and the code is cleared, the next step is to attempt to recreate the problem that made the computer set the code.
At times, the problem is easily spotted with a simple under hood inspection but often tracking down the problem requires monitoring the FRP data while wiggling the underhood electrical harness. If by wiggling a section of wire you notice the sensor data consistently reacts to manual manipulation, then the technician will have to isolate the problem area in the wiring harness.
Sometimes the code doesn’t come back immediately. In this case, the owner can decide whether to simply wait until the code comes back or have the sensor replaced. Often, a discussion with the owner is necessary at this point. Usually the price of the sensor is key. If it is on the less expensive side, it may be cost effective to replace the sensor; but if it is expensive, the customer may choose to do nothing and see if the code returns.
Common mistakes when diagnosing the P0194 code
It is common for a technician to want to test the fuel pressure with a mechanical fuel pressure gauge that taps directly into the fuel system. This is not advisable because of the excessively high and dangerous fuel pressure in these systems.
Diesel fuel systems have been designed to closely monitor fuel pressure. With the proper understanding of these systems, the monitoring systems should be used to diagnose the vehicle.
How serious is the P0194 code?
The seriousness of this code depends upon the symptoms the vehicle exhibits. This code can be set and the vehicle can still run just fine.
Often this code is a result of another problem such as the fuel pressure regulator or fuel pressure sensor. If there are symptoms aside from this code, these drivability symptoms should be addressed first. The other codes are usually the source of the problem and the P0194 code is a byproduct of those other problems.
What repairs can fix the P0194 code?
The possible fixes are dependent on the make and model of vehicle. Not all diesel injections systems use the same engineering. Here are some common fixes for the code:
Additional comments for consideration regarding the P0194 code.
It is important to know that this code is only used with diesel engines and not all manufactures will make use of this system check. The fuel system pressure in a diesel engine is much higher than a gas engine. A gas engine has 15-65 psi on average while a diesel engine has as much as 5500 psi.
Need help with a P0194 code?
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