|Code||Fault Location||Probable Cause|
|P1456|| P1456 – Fuel Tank Temperature Sensor Circuit Malfunction (Ford) |
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Manufacturer Specific Definitions for P1456
|Acura||Evaporative emission (EVAP) canister purge system (fuel tank system) - leak detected|
|Audi||Exhaust gas recirculation temperature (EGRT) control, Bank 1 - control limit reached|
|Citroen||Fuel Tank Temperature Sensor Circuit Malfunction|
|Honda||Evaporative emission (EVAP) canister purge system (fuel tank system) – leak detected|
|Infiniti||Evaporative emission (EVAP) canister purge system – very small leak|
|Isuzu||Evaporative emission (EVAP) canister purge system (fuel tank system) - leak detected|
|Mazda||Evaporative emission (EVAP) system|
|Nissan||Evaporative emission (EVAP) canister purge system – very small leak|
|Peugeot||Fuel Tank Temperature Sensor Circuit Malfunction|
|Porsche||A/C Compressor Control|
|Saab||Evaporative emission (EVAP) – small leak/fuel tank level sensor, in fuel tank – malfunction|
|Volkswagen||Exhaust gas recirculation temperature (EGRT) control, control limit reached|
Table of Contents
- What Does Code P1456 Mean?
- What are the common causes of code P1456?
- What are the symptoms of code P1456?
- How do you troubleshoot code P1456?
- Codes Related to P1456
- Get Help with P1456
What Does Code P1456 Mean?
SPECIAL NOTES ON CODE P1456
Be aware that although OBD II code P1456 is a manufacturer specific code, as indicated by the “P” followed by the letter “1”, the definition(s) assigned to it are NOT uniform across all manufacturers. Also take note that this guide deals with manufacturer-specific code P1456 as it applies to “Fuel Tank Temperature Sensor Circuit Malfunction”.
There are two predominant definitions in current use, either of which applies to different ADM (American Domestic Market), and imported European and Japanese vehicles;
- P1456 – “Fuel Tank Temperature Sensor Circuit Malfunction”
- P1456 – “EVAP Emission Control System Leak Detected”.
The above being the case, some cheap generic code readers may not always display the correct definition for code P1456: always refer to the relevant technical manual for the correct definition and diagnostic/repair procedures for code P1456 as it pertains to the application being worked on.
However, on some applications fuel temperature sensor-related problems can also be indicated by the generic code P0180 – “Fuel Temperature Sensor “A” Circuit Malfunction”, with the related codes being;
- P0181 – “Fuel Temperature Sensor “A” Circuit Performance”
- P0182 – “Fuel Temperature Sensor “A” Circuit Low Input.”
Refer to the Related Codes section of this guide for more definitions and applications of OBD II code P1456. END OF SPECIAL NOTES
P1456 – “Fuel Tank Temperature Sensor Circuit Malfunction”
OBD II fault code P1456 is defined as “Fuel Tank Temperature Sensor Circuit Malfunction”, and is set when the PCM (Powertrain Control Module) receives an abnormal voltage input from the fuel temperature sensor. What constitutes an “abnormal” signal varies between manufacturers; for the most part though, a code will be set and a warning light illuminated when the fuel temperature does not fall within a predefined range applicable to a particular application. Note that while a single failure will set the code on some applications, others may require several failure cycles to set code P1456.
In practical terms, the fuel temperature sensor is an inline microprocessor that has a dual role; it measures the actual fuel temperature in the tank one the one hand, and the amount of ethanol and other contaminants present in the fuel on the other. This is particularly important in the case of flex-fuel vehicles; since methanol has a lower calorific value than regular gasoline, the PCM has to make adjustments to the ignition timing, injector pulse width, and other settings to compensate for the lower calorific value of ethanol to maintain maximum power output while using the least amount of fuel.
In terms of its operation, the fuel temperature sensor, also known as the fuel composition sensor, or flex fuel sensor, continuously monitors all of the fuel that passes through it to provide the PCM with a continuous “analysis” of the fuel by means of a square wave form.
In practice, the frequency of the wave form varies according to the amount of ethanol or other contaminants present in the fuel, which variation is seen by the PCM as variations in temperature. The typical frequency range of the wave form is from around 50 Hertz, which represents clean, uncontaminated fuel, to about 150 Hertz, which represents 100% ethanol.
Note that the maximum allowable concentration of ethanol in gasoline may not exceed 85%, meaning that a wave form frequency of 150 Hertz is unlikely if the sensor and its control /signal circuits are fully functional. However, other contaminants such as water can increase the wave frequency, but in these cases, it is almost certain that misfiring codes due to the high water content will be present as well.
In addition, the actual temperature of the fuel is also measured. On most applications, fuel at a temperature of -400F will produce a signal (voltage) pulse width of 1 millisecond, while fuel at a temperature of 2570F (1250C) will produce a signal pulse width of 5 milliseconds. From this it should be clear that the higher the fuel temperature, the longer the interval between sequential signal pulses becomes. However, these values differ between applications; always consult the relevant manual for the application being worked on for the correct values.
The image below shows the typical location of the fuel temperature sensor in the fuel pump canister. Note however that the actual location may differ from that shown here- always consult the manual for the application being worked on to locate the fuel temperature sensor to prevent wasting time looking for a component that could be located elsewhere.
What are the common causes of code P1456?
Although fuel pump failure can contribute to setting code P1456, there is almost certain to be fuel pressure related codes present if the pump is a contributing factor. Other possible causes of code P1456 could include the following-
- Damaged, burnt, shorted, or corroded wiring and/or connectors.
- Open circuits.
- Defective fuel temperature sensors.
- Defective PCM. Note that is a rare event, and the fault must be sought elsewhere before any controller is replaced.
What are the symptoms of code P1456?
In some cases, the only symptoms present may be a stored trouble code and an illuminated warning light. However, other applications may display symptoms, such as the following-
- Misfiring codes may be present. Note that misfires can vary from slight and barely detectable, to severe conditions that can influence idle quality and even overall engine performance.
- Hesitation upon acceleration may be present.
- Hard, or no start conditions may develop.
- Other fuel system-related codes may be present.
Note that applications that are designed to run on high concentrations of ethanol are less likely to display severe symptoms than applications that do not carry the “flex-fuel” designation, which are mostly older vehicles.
How do you troubleshoot code P1456?
NOTE #1: Apart from a good quality digital multimeter, an oscilloscope is a required item to diagnose code P1456, since analysis of wave forms is required. If an oscilloscope is not available, the better option is to refer the vehicle for professional diagnosis and repair.
NOTE #2: When diagnosing code P1456, it is always a good idea to check the actual fuel temperature independently with a high quality thermometer to prevent a possible misdiagnosis, and the unnecessary replacement of components.
Record all codes present, as well as all available freeze frame data. This information can useful should an intermittent fault be diagnosed later on.
NOTE: Bear in mind that on some applications, the conditions that set code P1456 can also set other fuel system and misfiring codes. To check if this is the case, clear all codes and operate the vehicle to see which (if any) codes return. If the same codes return, and in the same order, it is likely that code P1456 is the root cause of the other codes. In these cases, resolving code P1456 will likely resolve the other codes as well.
Consult the manual to determine the location, color-coding, routing, and function of each wire in the circuit, and perform a thorough visual inspection of all associated wiring. Look for damaged, shorted, burnt, or corroded wiring and connectors, and make repairs as required.
Clear all codes when repairs are complete, and rescan the system to see if any codes return.
If the code persists, prepare to perform ground, reference voltage, resistance, and continuity checks on all associated wiring. Be sure to disconnect the temperature sensor system from the PCM to avoid damage to the controller.
Pay particular attention to the reference voltage- on most applications this should be 5 volts (supplied by the PCM), but consult the manual on this value. Also check the resistance of the signal wire between the sensor and the PCM carefully, as well as all ground connections. On some applications the ground is supplied by the PCM, so consult the manual on the correct procedure (KOER/KOEO) to establish the ground connection.
All values should match those stated in the manual exactly; compare all obtained readings to those stated in the manual, and repair/replace wiring to ensure that all values fall within the manufacturer’s specifications.
Clear all codes, and retest the system after repairs are completed to see if the code returns.
If all electrical values fall within the manufacturer’s specifications, suspect a defective fuel temperature sensor. If an oscilloscope is not available, refer the vehicle for professional diagnosis and repair.
If an oscilloscope is available, and you are comfortable with using it, consult the manual to locate the fuel temperature sensor, and connect the positive lead to the sensor signal wire, and the negative lead to a suitable vehicle ground. Activate the circuit- the oscilloscope will display a square wave form, similar in shape to the teeth on a wheel speed sensor,
SPECIAL NOTE: Interpreting the data can be tricky, which is why it is important to have the actual fuel temperature available. Obtain a quantity of fuel from the vehicle, and check the actual temperature with a high quality thermometer before drawing any conclusions based on the oscilloscope data.
Even with the actual fuel temperature available, small deviations from the recommended pulse width may not be readily apparent, especially on oscilloscopes that do not display wave form frequencies as numerical values in addition to the actual wave form. Nonetheless, if the fuel temperature sensor is defective, the deviations are bound to be large, so compare the displayed wave with the diagrams in the manual.
If it obvious that the oscilloscope data and the diagrams do not agree, it is safe to assume that the sensor is defective. Assuming that all obtained electrical values conform to specified values, replacement of the fuel temperature sensor will usually resolve the problem.
If however, the oscilloscope data and the diagrams agree, it is safe to assume that the PCM is defective, but take note that this is a relatively rare event, and the fault must be sought elsewhere before any controller is replaced.
If the fuel temperature sensor is replaced, clear all codes, and retest the system to see if any codes return. If no codes return, operate the vehicle for several drive cycles and retest the system. If the code does not return, the repair can be considered to have been successful.
If the code does return after several drive cycles, it is likely that an intermittent fault is present. Note that some intermittent faults can be extremely challenging to find and repair, and in some cases the fault may have to be allowed to worsen before an accurate diagnosis and definitive repair can be made.
Codes Related to P1456
- Acura – “EVAP Emission Control System Leak Detected”
- Honda – “Evaporative Emissions (EVAP) Control System Leakage”
- BMW – “Heated Catalyst Heater Power Supply Open Circuit (Bank 1)”
- Nissan – “EVAP Control System”
- Porsche – “A/C Compressor Control”
- Saab – “Tank purging, leak in system”
- Volkswagen/Audi – “Exhaust gas temperature control limit attained (Bank 1)”
- Volvo – “Exhaust gas temperature control limit attained (Bank 1)”
- GM – “Catalyst Heater Diagnostic”
Note that this list of alternative definitions of code P1456 must not be regarded as complete or definitive. European and Japanese car makers are not bound by the rules that determine fault code definitions in the ADM, which means that new models from foreign markets and manufacturers may have still different definitions assigned to code P1456.
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