P0094 Fuel System Leak Detected – Small Leak
OBD-II Trouble Code Technical Description
Fuel System Leak Detected – Small Leak
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to all 1996-newer vehicles (Ford, GMC, Chevrolet, VW, Dodge, etc.). Although generic, the specific repair steps may vary depending on make/model.
When I come across a stored code P0094, it generally means that the powertrain control module (PCM) has detected a substantial decrease in fuel pressure. Fuel pressure specifications vary from one manufacturer to another and the PCM is programmed to monitor fuel pressure according to these specifications. This code is primarily used in diesel powered vehicles.
Diesel fuel systems are monitored (by the PCM) using one or more fuel pressure sensors. Low pressure fuel is pumped from the storage tank to the high pressure injector pump via a supply (or transfer) pump that is usually either attached to the frame rail or inside the fuel tank. Once the fuel exits the injector pump, it can reach levels as high as 2,500 psi. Use caution when testing fuel pressure. These extreme fuel pressure conditions can be very hazardous. Although diesel fuel is not as combustible as gasoline, it is highly flammable especially under high pressure. Additionally, diesel fuel under these levels of pressure can penetrate the skin and enter the bloodstream. This can be harmful or even fatal under certain circumstances.
Fuel pressure sensors are placed at strategic locations in the fuel delivery system. Typically, there will be at least one fuel pressure sensor for each segment of the fuel system; a sensor for the low pressure supply end and another for the high pressure delivery end.
The fuel pressure sensors are normally of a three-wire design. Some manufacturers use battery voltage and others use a lesser degree of voltage (usually five-volts) as a reference for the PCM. Reference voltage and a ground signal are supplied to the sensor. The sensor provides the PCM with a voltage input signal. As fuel system pressure increases, the resistance level of the fuel pressure sensor decreases, allowing the voltage signal that is input to the PCM to increase accordingly. When fuel pressure decreases, resistance levels in the fuel pressure sensor increase, causing the voltage input signal to the PCM to decrease. If the fuel pressure sensor/s is operating normally, this cycle takes effect with each ignition cycle.
If the PCM detects fuel system pressure that does not coincide with programmed specifications, during a set period of time and under certain circumstances, a code P0094 will be stored and a malfunction indicator lamp may be illuminated.
Severity & Symptoms
Given the potential for a vehicle fire, as well as the distinct possibility of diminished fuel efficiency that can be associated with a stored P0094 code, it should be addressed with a great degree of urgency.
Symptoms of a P0094 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
I would gain access to a suitable diagnostic scanner, a diesel fuel pressure gauge, a digital volt/ohmmeter (DVOM), and a vehicle service manual or a subscription to All Data (DIY), when attempting to diagnose a code of this type.
I typically begin my diagnosis with a visual inspection of fuel lines and components. If any leaks are discovered, repair them and recheck the system. Inspect system wiring and connectors at this time.
Connect the scanner to the vehicle diagnostic connector and retrieve al stored codes and freeze frame data. Write this information down in case this proves to be an intermittent code, which will prove much more difficult to diagnose. If other fuel system related codes are present, you may want to diagnose them first before attempting to diagnose the P0094. Clear the codes and test drive the vehicle.
If the P0094 is immediately reset, locate the data stream of the scanner and observe fuel pressure readings. By narrowing the data stream to include only pertinent data, you will get a quicker response. Compare the actual reflected fuel pressure readings with manufacturer’s specifications.
If fuel pressure is not within specs, use the fuel pressure gauge to test system pressure in the appropriate quadrant. If actual fuel pressure readings are not within manufacturer’s recommended specifications, suspect a mechanical failure. Continue by disconnecting the fuel pressure sensor connector and testing the resistance of the sensor itself. If the sensor resistance does not comply with manufacturer’s specifications, replace it and retest the system.
If the sensor checks out, disconnect all related controllers and begin testing system circuits for resistance and continuity. Repair or replace shorted or open circuits as required.
If all system sensors and circuitry seems normal, suspect a defective PCM or PCM programming error.
Additional diagnostic tips:
See also: P0093 Fuel System Leak Detected – Large Leak
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"Delete Error Code Permanently, Disable DTC Error Code Function for p0094 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p0094 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p0094.
