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OBD Trouble Codes

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OBD-II is the new standard of Onboard Diagnostic Systems and are in most cars and trucks on the road today. The OBD-II is a diagnostic computer that is hooked up to your car to control engine functions and diagnose problems. If there is a problem with a component of the vehicle, a trouble code will be given. Here some of the most common trouble codes, what they mean, what symptoms to look for, and some solutions to solving the problem, from the OBD Codes.com trouble code database.


What Does it Mean? P0440 is the trouble code given when the evaporative emission control system has malfunctioned. The EVAP system contains the gas cap, fuel lines, carbon canister, purge valve, and other hoses within the car. The EVAP emission control system prevents fuel vapors from escaping from the fuel system of a vehicle


There will most likely not be any noticeable drivability symptoms.


Diagnoses can be tricky with a P0440 sometimes, so there is no one way to remedy the problem. Here are some suggested diagnostics:

  • Remove and install the gas cap, clear the code, and drive for a day to see if the code comes back.
  • Inspect the EVAP system for cuts and holes in the tubes or hoses.
  • Inspect for damaged or disconnected hoses around the EVAP purge solenoid
  • Check and/or replace the sensor
  • Check and/or replace the purge valve
  • Have a professional use a smoke machine to detect leaks


What Does it Mean? This code indicates that a part of the Evaporative emission control system has an incorrect purge flow. The EVAP emission canister purge is controlled by a valve which pulls fuel vapor from the fuel tank and into the engine to be burned. If the switch is closed, indicating no detected purge flow, this error will appear.


Usually no symptoms are detectable by the driver.


Diagnoses can be difficult sometimes with a P0441 code, but here are some suggestions:

  • Replace leak detection pump
  • Replace PCM
  • Replace resistance in purge connector
  • Replace vacuum switch
  • Repair damaged EVAP lines or canister


What Does it Mean? This trouble code indicates that there is a small leak in the EVAP emission control system.


You most likely will not notice anything


The most common repairs for a P0442 is the remove and reinstall the gas cap, replace the gas cap, and inspect the EVAP system for cut or holes in the tubes and hoses.


What Does it Mean? This trouble code is given when the EVAP emission control system purge control valve circuit is malfunctioning. If the purge solenoid does not activate, the ECM will not see the expected voltages from the ground circuit, or will sense an open in the circuit, producing this code.


Sometimes P0443 only shows up as a malfunction indicator light (MIL) illumination, but sometimes a rough-running engine can be a symptom of this problem.


Use a scan tool to command the purge solenoid to activate. You should hear or feel a clicking as it activates. If this does not work, unplug the connector and examine the solenoid for water damage or corrosion. Check for voltage from the battery, and if any is detected, ground the control side manually with a jumper wire and listen for the valve to click. If it does, this means that the problem is with the control circuit, not with the solenoid itself. If there is no click, replace the solenoid. To check for a problem with the control circuit, remove the ground from the ECM connector and plug the solenoid back in. Turn the key on, and manually ground the purge valve control wire. If the solenoid clicks, there is no problem with the wire to the solenoid, and the problem is with the purge solenoid driver circuit in the ECM. Replace the ECM, and the problem should be fixed. If the solenoid does not click, there is an open in the wiring between the solenoid and ECM that must be found and repaired.


What Does it Mean? The P0446 code indicates that the EVAP emission control system vent control circuit has malfunctioned. If the ECM detects a short to the ground, an open, or a short in the battery, P0446 will appear. This code may also indicate that the EVAP system cannot achieve or hold a vacuum during testing.


The only indication of a problem will be a MIL illumination.


There are a few things to try if you are receiving a P0446 code. First is to replace the vent valve. Repair the open, short or resistance problem in the control circuit and power circuit. And finally, if none of that works, replace the PCM.


What Does it Mean? This code indicates that the EVAP emissions control system pressure system has high output. Simply put, this means that there is a large amount of pressure (above 4.5 volts,) in the EVAP system.


There usually are no symptoms associated with this code aside from MIL illumination. Sometimes a fuel odor can be detected.


Check the value of the FTP sensor with a scan tool with the key on and engine off. The normal value is around 2.5 volts, and never over 4.5 volts. If the value is close to 2.7 volts with the gas cap off, measure the voltage of the signal wire with a digital volt ohm meter, and wiggle the wiring at the FTP sensor. If the voltage fluctuates, check for a problem with the connector.

If the value on the scan tool shows 4.5 volts or higher, unplug the sensor if possible, and check the voltage again. If the high voltage is still present, check for a short in the wiring harness to the voltage on the signal wire. If you have a good ground and still are detecting high voltage, replace the FTP sensor.


What Does it Mean? A P0455 code means that a leak in the EVAP emission control system has been detected.


There will likely be no drivability issues.


Remove and reinstall the gas cap. Drive the car for a day and recheck codes. If codes return, replace the gas cap and/or inspect the EVAP system for cuts or holes in the tubes and hose and repair if needed.


What Does it Mean? The P0456 trouble code means that the EVAP emissions system has a small leak.


There will likely be no symptoms aside from the MIL being illuminated.


Using a scan tool, activate the vent solenoid and seal the system. Monitor the FTP sensor. If the system seals properly, the number will stay consistent. If the number changes, use a smoke machine and watch for the smoke exiting at any EVAP component. Replace the component that releases smoke, as it is the faulty component.


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