Codes are po456 and po463
DTC P0456 - Evaporative Emissions System - Small leak detected
The Powertrain Control Module (PCM) at different times performs various tests on the EVAP system. OBD II Enhanced EVAP systems are in place to keep fuel tank vapors from venting into the atmosphere, and instead purges them into the engine to be burned. Regular pressure tests are conducted by the PCM to monitor the sealed system for leaks. The PCM monitors the EVAP system pressure by watching the fuel tank pressure (FTP) sensor. When the sensor indicates a small leak in the EVAP system, this code is set.
Potential Symptoms: there will likely be no noticeable symptoms other than the Malfunction Indicator Lamp (MIL). This is because the EVAP system is a closed system and only controls fuel tank vapors, not engine management.
Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivable cause this code as well or if the cap wasn't properly tightened. Any of the following could also be the cause:
- A small leak in any of the EVAP hoses or fuel tank hoses
- A small leak in the purge valve or vent valve
- The EVAP Canister may be leaking
About possible solutions, first, using a scan tool activate the vent solenoid, sealing the system. Then monitor the fuel tank pressure (FTP) sensor. If the system is sealing properly, the number will stay consistent. If is isn't, the pressure sensor will show that as well. If the system slowly leaks, use a smoke machine and watch for smoke exiting the system at any EVAP component. Any where there is smoke exiting the system, that is the faulty component. Do not pressurize the EVAP system with air pressure. Doing so can damage the purge and vent solenoids in the system.
DTC P0463 - Fuel Level Sensor Circuit High Input
The fuel level sensor (sender) is located in the fuel tank usually integral to the fuel pump module. Usually they cannot be replaced without replacing the fuel pump module, though there are exceptions. There is a float attached to an arm that travels along a resistor which is grounded to the tank, frame or has a dedicated ground circuit. Voltage is supplied to the sender and the ground path changes according to fuel level. How much voltage depends on the system but 5 volts isn't uncommon.
As the fuel level changes, the float moves the arm and changes the resistance to ground which varies the voltage signal. This signal may travel to a fuel pump computer module or directly to the instrument cluster module. Depending on the system, the fuel pump computer module may only monitor the resistance to ground and then relay the fuel level information to the instrument panel. If the fuel level signal to the fuel pump module (or instrument cluster module or PCM (powertrain control module)) goes above 5 volts for a specific amount of time, then the module that is monitoring the fuel level circuit will record this fault code.
Symptoms of a P0463 DTC may include:
Mil (Malfunction indicator lamp) illumination
Fuel level gauge may fluctuate abnormally or read empty or full
Fuel light may illuminate and sound alarm
Potential causes of a P0463 code include:
The signal circuit to the fuel sender is open or shorted to B+ (Battery voltage)
The ground circuit is open, or ground path may have high resistance due to rust or missing ground ******** fuel tank
Damage to the fuel tank could cause problem in fuel level circuit
There's an open in the fuel lever sensor's resistor to ground
Possibly faulty instrument cluster
Less likely is the possibility that the PCM, BCM, or Fuel pump computer module has failed
Now, about the possible solutions, keep in mind that fuel pump senders normally last the life of the fuel pump. So if you have this code present, do a visual inspection of the fuel tank and wiring harness. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender. Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector. Repair as needed. Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness. If not, repair the open or short in the wiring.
Doing a voltage drop test on the ground circuit can determine if there is a high resistance path in the ground circuit. You can perform this by using a voltmeter and connecting one lead to the battery ground post and the other to the fuel level sensor ground at the tank. Turn the key on (preferably the engine should be running). Ideally it should be 100 millivolts or less (.1 volts). Anything close to 1 volt indicates a current problem or a developing problem. Repair/clean the fuel level sensor ground as needed. It's not impossible that the instrument cluster has failed internally or on the printed circuit board (if applicable). These are very difficult for the layman to test. But if you have access to a wiring diagram you may be able to remove the cluster and see the damaged circuit if it's located on the printed circuit board, but otherwise you'll need a scan tool that will communicate with the instrument cluster.
A simple way to test the fuel level circuit is to provide a good ground to the fuel level sensor at the fuel tank connector. With the key on the fuel gauge should go to one extreme or the other. Removing the ground path completely should cause the gauge to do the opposite. If the gauge responds, you know the wiring that supplies voltage and ground to the fuel level sensor is good and that the instrument cluster is likely okay. The likely suspect would be the fuel level sensor itself. The fuel tank may need removal to gain access to the fuel pump module in the tank. A PCM or BCM (Body control module) failure isn't impossible but highly unlikely. Don't suspect this first.
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Jul 04, 2012 |
Cars & Trucks