|Trouble Code||Fault Location||Probable Cause|
|P1304||Cylinder Number 4 Random Misfire Detected (ACURA, HONDA)
Misfiring Cylinder 4 (BMW, MINI)
EGR Calibration High (FORD)
Phase Sensor (HYUNDAI)
Cylinder 4 Misfiring Detected (SAAB)
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What Does Code P1304 Mean?
Special note on trouble code P1304 and Ford, Lincoln, Mercury, and Oldsmobile vehicles: While DTC P1304 is a manufacturer-specific code that may affect several OBD II compliant vehicles, the causes and symptoms of this code typically vary between most vehicle makes. This article will therefore deal with code P1304 as it applies specifically to Ford, Lincoln, Mercury, and Oldsmobile vehicles.
OBD II fault code P1304 is a manufacturer-specific trouble code that is defined by carmaker(s) Ford, Lincoln, Mercury, and Oldsmobile as “EGR Calibration High”, and is set when the PCM (Powertrain Control Module) detects abnormal, unexpected or implausible calibration settings/parameters in the EGR (Exhaust Gas Recirculation) system.
NOTE: Code P1304 applies to all Ford diesel and gasoline applications that are not fitted with variable valve/camshaft timing systems since VVT/VCT systems perform the same functions as EGR systems as a natural consequence of their operation.
The purpose of EGR systems in all applications is to introduce precisely metered amounts of exhaust gas into the cylinders under some operating conditions to prevent the formation of harmful exhaust emissions such as NOx (oxides of nitrogen) at high combustion temperatures. In practice, the addition of exhaust gas into the engine has a quenching effect on the combustion flame, and provided the EGR system is fully functional, the added exhaust gas will prevent combustion temperature from exceeding 2 5000F, above which NOx is formed at large throttle openings.
During normal operation of an engine, though, exhaust gas is prevented from entering the engine at idling or low engine speeds and loads, since the exhaust gas also has a diluting effect on the air/fuel mixture, which can seriously reduce engine performance at low speeds.
However, the subject of EGR control strategies is a highly technical one, and, therefore, the finer details of these systems fall outside the scope of this article. Moreover, since diagnosing and fixing the multitude of issues that (can) affect the proper operation of EGR systems on Ford applications require skills, knowledge, and equipment that DIY mechanics typically do not have access to, we will describe the operation of the latest iteration of EGR systems on Ford applications in broad strokes below-
In terms of operation, the EGR valve is, located on the inlet manifold, between the exhaust system and the manifold. In their simplest form, EGR valves are fitted with diaphragms that are controlled by a vacuum-operated actuator, which is in its turn, controlled by a dedicated electronic control module. It is perhaps worth mentioning at this point that the amount of exhaust gas that is introduced into an engine at any given time is solely determined by a) the engine design/type, and b), the validity/plausibility of input data the control module receives from various engine sensors.
These sensors typically include the-
- barometric pressure sensor
- manifold absolute pressure sensor
- engine coolant temperature sensor
- intake air temperature sensor
- boost pressure sensor
- engine speed sensor
- throttle position sensor
- one or more exhaust backpressure sensors
- throttle pedal position sensor (if fitted)
- and others, that include various sensors in and around the automatic transmission
Thus, assuming that all the above sensors, and of course, the EGR valve) are in perfect working condition, that all their readings correlate, and that operating conditions are suitable for the introduction of exhaust gas, the control module will command the vacuum actuator to open the EGR valve by a set amount. This setting is monitored by a position sensor on the EGR valve’s pintle, and this position is used by the control module to infer the amount of exhaust gas that is flowing through the EGR valve.
This is the only method available to the control module to “measure” the amount of exhaust gas flowing through the EGR valve, although, in older systems that used DPFE-based methods, the control module could measure the actual amount of exhaust gas flowing into the engine by using a pressure differential between various parts of the system.
Nonetheless, since the maximum allowable amount of exhaust gas that can be introduced is based on the engine type/design, the EGR valve and its vacuum actuator are calibrated to form an essential part of the overall engine and fuel management systems. As a practical matter, then, this means that the EGR valve can only open when, amongst other things-
- the engine coolant temperature is above a predefined threshold
- the engine speed is above a minimum allowable threshold
- the throttle opening is bigger than a minimum allowable setting
- the readings from all implicated sensors not only correlate with each other but that they correlate within an acceptable or pre-defined range of readings
Collectively, the above requirements constitute a set of calibration parameters, which vary not only between Ford engine types and designs but also between identical models from different production years.
Thus, when the PCM (or another control module) detects a failure, malfunction, or miscorrelation between implicated sensors and/or components that cause an implausible or incorrect calibration parameter, it will recognize that it cannot control the EGR system effectively. When this happens, the PCM will set code P1304 as a pending code, but it may only illuminate a warning light when it detects failures, malfunctions, and/or miscorrelations during the second of two consecutive drive cycles.
Where is the P1304 sensor located?
This image shows the location (arrowed) of the EGR valve on a 2.3L Ford Ranger application. Note though that while most modern EGR valves follow this general pattern, and are therefore relatively easy to locate and identify, some EGR valves may not look like this example at all.
Therefore, it is recommended that you consult reliable and up-to-date service information for the affected application to locate and identify the EGR valve correctly. Also, be aware that on some Ford applications, it may be necessary to remove and/or disassemble various unrelated engine parts/components to gain easy access to the EGR valve for testing or replacement.
WARNING: EGR valves are application specific, and are therefore NOT interchangeable, even with units that might appear to be identical to the original part.
What are the common causes of code P1304?
Typical causes of code P1304 on Ford vehicles are many and varied, but could include one or more of the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors associated with any implicated sensor and/or component
- Defects in, or malfunctions of one or more implicated sensors or components
- Dislodged, ruptured, or split vacuum hose(s)
- Damaged and/or perforated diaphragm in either (or both) the vacuum actuator or EGR valve
- Defective or malfunctioning EGR valve position sensor
- Miscorrelations between two or more implicated sensors, with miscorrelations between the MAP (Manifold Absolute Pressure) sensor and the Barometric Pressure Sensor perhaps being the most common instance of miscorrelations. Note that this will be indicated by the presence of code P0069 – “MAP – Barometric Pressure Correlation”
- Damaged or corrupted software
- Failure to perform a proper calibration procedure (if required) during previous repair attempts
- Failed or failing PCM, but note that since this a rare event, the fault must be sought elsewhere before any control module is reprogrammed or replaced
What are the symptoms of code P1304?
Typical symptoms of code P1304 could include one or more of the following, but note that depending on both the application and the nature of the problem, the severity of one or more symptoms listed here could vary between applications-
- Stored trouble code and possibly an illuminated warning light
- Depending on the nature of the problem, multiple additional codes may be present along with P1304
- Various degrees of power loss may be present, with the severity of the power loss depending on both the application and the nature of the problem
- The idling quality may be rough, or erratic. In some cases, the engine may not idle at all
- Hard starting, or in some cases, a no-start condition may be present
- The engine may hesitate or stumble upon acceleration
- The engine may stall frequently and mostly unexpectedly at low engine speeds
- Fuel consumption may increase dramatically
- Random or intermittent misfires may be present
- The engine may emit loud knocking noises during acceleration as a result of uncontrolled and/or premature combustion
- Depending on the nature of the problem, the vehicle may emit thick clouds of black smoke from the tailpipe under acceleration
- Acceleration may be poor
- One or more readiness monitor may not initiate, or may not run to completion
- The vehicle will fail an emissions test
- While it is rare for Ford applications to enter into a limp mode as a result of EGR issues, it does happen, and in most cases, the limp mode will persist until the problem is found and corrected
Other Manufacturer Specific Definitions for P1304EGR Calibration High (Ford)
Cylinder No. 4 - misfire (Acura)
Heated Catalyst Battery Temperature Sensor 1 Electrical (BMW)
Cylinder Number 4 Random Misfire Detected (Honda)
Phase Sensor (Hyundai)
Cylinder 4 – misfire detected (Land Rover)
Misfiring Cylinder 4 (Mini)
Cylinder 4 – misfire detected (Saab)