P0462 – Fuel tank level sensor -low input

Reinier

By Reinier (Contact Me)
Last Updated 2016-08-17
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0462 Fuel tank level sensor -low input Wiring short to earth, fuel tank level sensor, ECM

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What Does Code P0462 Mean?

OBD II fault code P0462 is defined as “Fuel Level Sensor Circuit Low Input”, and is set when the PCM (Powertrain Control Module) or BCM (Body Control Module on some applications) detects a signal from the fuel level sender unit that indicates a fuel level that exceeds the fuel tank’s capacity.

The PCM or BCM does not “know” how much fuel is in the fuel tank: the only information the controller has about the fuel level derives from the signal voltage generated by the sender unit. Therefore, regardless of whether the tank is full or empty, the controller expects to see a predefined signal voltage that corresponds to that state, which means that if say, a short circuit (or any other problem) creates a resistance that is inconsistent with either state, the controller will set code P0462 and illuminate a warning light.

Put in another way, if the sender unit’s input circuit is fully functional, code P0462 will typically not be set when a mechanical problem prevents movement of the float arm. All that will happen in this case is that the fuel gauge reading will not reflect changes in the actual fuel level in the tank.

In terms of operation, fuel level sender units use variable resistors to indicate the actual fuel level in the tank. In practical terms, this is accomplished by means of a float that is attached to a moveable arm, the other end of which is in contact with a variable resistor. As the fuel level changes, the movable arm either rises or drops, which brings the contact point of the arm into contact with different parts of the variable resistor.

Thus, when the tank is empty, the resistor will generate the minimum reference voltage for that application because there is more resistant material for the current to pass through, which results in a lower voltage reaching the fuel gauge, giving an “Empty” reading. Conversely, when the tank is full, the resistance decreases, resulting in close to the maximum signal voltage being sent to the fuel gauge, thus producing a “Full” reading.

While the basic operating principles of fuel level sender units are much the same across all manufacturers, there are two notable exceptions to this rule. Ford and GM generally switch the electrical resistance around, meaning that on these makes the maximum signal voltage is generated when the tank is empty and vice versa: the minimum signal voltage is generated when the tank is full.

The image below shows the typical construction of a fuel pump canister. Note the fuel level sender unit that forms part of the canister. Be aware that not all level sender units are incorporated into the pump canister; on some applications the sender unit is mounted separately.

Fuel level sending unit

Note: 

Circuit Low Input codes are often the result of low battery voltages (that can have many possible causes), bad connections across electrical connectors or previously repaired wiring, as well as corrosion in electrical connectors. Other possible causes of low input voltages include poor installation of aftermarket components, poor quality aftermarket components like fuses, relays, and switches, and modification of the electrical system that could include the use of conductors that are not rated for use in a particular application. However, poor connections often result in high resistances in some parts of the circuit, which is why it is important to perform resistance and continuity checks during the diagnostic procedure.

What are the common causes of code P0462 ?

Typical causes of code P0462 are much the same across all applications, and these could include the following-

  • Burnt, damaged, shorted, or corroded wiring and/or connectors.
  • Open circuits.
  • Loss of ground.
  • Defective fuel level sender unit.
  • Damage to the fuel tank that inhibits the free movement of the moveable arm. Note that not all applications will set the code if damage to the fuel tank occurs.
  • Defective PCM/BCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced.

NOTE: On some Ford products, fuel with high sulphur content can cause the build-up of a type of varnish on the variable resistor, which build-up prevents contact between the resistor and the moveable contact, thus setting code P0462.  While some aftermarket fuel additives might assist in removing the varnish deposit, the better option is to replace the fuel level sensor unit.

What are the symptoms of code P0462 ?

Apart from a stored trouble code and an illuminated warning light, the symptoms of code P0462 typically include the following-

  • Indicated fuel level may be different from the actual level.
  • Low fuel level warning light may flash, or be illuminated permanently despite there being sufficient fuel in the tank not to trigger the low level warning.
  • Engine may shut off or not start due to lack of fuel, despite the fuel gauge registering readings above “Empty”.
  • In some cases, the self diagnostic system may display “EVAP System Not Ready” messages when it cannot register an accurate fuel level.

How do you troubleshoot code P0462 ?

NOTE #1: Before attempting a diagnosis of code P0462, consult the manual on the type of sender unit the application is fitted with. Most new applications are fitted with magnetic fuel gauges that depend on a varying magnetic field to deflect the indicating needle. Although the basic operating principle remains the same on these systems, i.e., a variable resistance that varies the gauge input voltage, the resistances involved are generally much higher than those found on other designs.

In addition, almost all magnetic fuel gauges follow the example set by GM: the lower the fuel level, the lower the resistance, and vice versa. Also be aware that the fast response time seen on a magnetic fuel gauge is a function of its design, and it does not indicate a short circuit as it sometimes would on a purely resistance-type gauge.

NOTE #2: Always refer to the manual for the application being worked on for the correct resistance values, because while the typical signal voltage across all manufacturers is around 5 volts, the electrical resistance that produces “Empty” or “Full” readings on the fuel gauge varies considerably between applications.

NOTE #3: Code P0462 specifically refers to issues in the fuel level sender unit input circuit, even though incorrect or erratic fuel gauge readings can also be caused by short circuits and other problems between the sender unit and the fuel gauge.

NOTE #4: When diagnosing code P0462, make sure that the fuel tank holds between 25%, and 75% of its capacity, since the self diagnostic program on most applications requires specific amounts of fuel to be in the tank before self diagnostic tests can be completed. Trying to diagnose this code with a low (or too high) fuel level can lead to misdiagnoses and hours of wasted time.

Step 1

Record all codes present, as well as all available freeze frame data. This information can be useful should an intermittent fault be diagnosed later on.

Step 2

Consult the manual on the location, function, color-coding, and routing of all wiring and fuses associated with the fuel sender unit, and perform a thorough visual inspection of all wiring. Look for damaged, burnt, disconnected, shorted, and corroded wiring, connectors, and fuses. Make repairs as required, clear all codes, and retest the system to see if the code returns.

NOTE #1: In some cases it may be necessary to remove the fuel tank from the vehicle to gain access to all wiring. Removing the tank is considerably easier with the vehicle on a hoist or vehicle lift: however, if a lift is not available, ALWAYS use properly rated jack stands to support the vehicle while removing the tank. Moreover, always observe basic safety rules, and NEVER smoke while working on a vehicle’s fuel system.

NOTE #2: When removing a fuel tank, always make notes, or take pictures of the routing and location of all wiring, fuel/vacuum lines, and other components. It is very easy to pinch wiring or fuel/vacuum lines during reassembly, which could lead to the fuel/EVAP system not working. It also goes without saying that all connections of hoses and lines must be made to industry standards during reassembly to avoid the possibility of leaks or other issues.

Step 3

If no visible damage to wiring and/or connectors is found perform resistance, continuity, ground, and reference voltage tests on all associated wiring, but be sure to disconnect the fuel level sender unit from the PCM/BCM to prevent damage to the controller.  Compare all obtained readings to those stated in the manual, but pay particular attention to the ground wire(s) and connection(s), since the sender unit relies on a sound ground to work at all.

Test the sender units’ ground by comparing it to a voltage drop test between the battery positive terminal and a suitable ground on the vehicle frame. The difference between the two voltage drop tests should not be greater than about 100 millivolts. Greater values indicate a malfunction in the input circuit. Make repairs or replace wiring as required to ensure that all readings fall within specifications, clear all codes, and retest the system to see if the code returns.

Step 4

If the code persists despite all electrical values falling within specifications, test the sender unit itself by unplugging it from the system where it connects to the wiring harness. Depending on the application, the indicating needle on the gauge will move to either the “Full” or the “Empty” position. Note that the needle will move past either point, or to built-in stops in the gauge, thus, as far as it can go.

If the gauge needle does this, both the sender unit and associated wiring are fully functional. Note however that on some applications the needle may move rather slowly, so allow enough time for the needle to reach its point of maximum deflection before drawing any conclusions from this test.

Step 5

If unplugging the sender unit does not produce maximum needle deflection, and it is certain that all electrical values fall within specifications it is safe to assume that the sender unit is defective. Be aware though that replacing the fuel level sender unit is more difficult on some applications than on others- in some cases, special tools may be required to remove the locking ring that secures the fuel pump canister. Always consult the manual on the correct (and safest) procedure to remove the fuel tank, or on how to gain access to the sender unit by removing seats and other items such as carpets.

Note that fuel sender units can typically not be repaired, but to avoid compatibility issues with the application’s electrical system, only ever replace a sender unit with an OEM part. While an aftermarket sender unit may fit the application, it often happens that the resistance rating of an aftermarket unit does not match the specifications of the application it is fitted to, which could result in inaccurate fuel level readings, or even fuel level readings that could indicate the tank is full when it is in fact empty.

WARNING: It is very important to take extreme care when fitting a fuel level sender unit. Any damage to the movable arm, for instance, barely noticeable bending or deformation of the arm could cause wildly inaccurate fuel level readings.

Step 6

If the code persists despite having completed the repair procedure outlined above, it is likely that an intermittent fault is present. Be aware though that intermittent faults can often be extremely challenging and time consuming to find and repair, and in extreme cases the fault may have to be allowed to worsen considerably before an accurate diagnosis and definitive repair can be made.

Codes Related to P0462

  • P0460Relates toFuel Level Sensor Circuit Malfunction”
  • P0461Relates toFuel Level Sensor Circuit Range/Performance”
  • P0462Relates toFuel level Sensor Circuit Low Input”
  • P0463Relates toFuel Level Sensor Circuit High Input”
  • P0464Relates toFuel level Sensor Circuit Intermittent”

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