Temporary Blockages:

During the winter season in cold weather climates, it is important to note that "temporary blockages" such as ice in the vapor lines may occur and set a DTC code. Be sure to inspect vapor lines for such temporary blockages as moisture and foreign material, including the plastic tube located in the "Fresh Air" circuit which is located inside the frame rail of the vehicle. If foreign material and/or moisture is found in the vapor lines, blow out the vapor line with compressed air ONLY after performing the following:

^ Remove any components (valves, air filter, canister etc.) from the vapor line to be cleaned.

^ Use a bag, rag or other retaining device to catch the foreign material and prevent it from contaminating other segments of the circuit.

WARRANTY INFORMATION:

Normal warranty operation codes and times apply.

This is the system self check that occurs 16 minutes after the vehicle is started and idling.

^ Canister Close Valve Check (P0446) - The canister close valve is open (at battery voltage) and the canister purge valve is closed (at battery voltage). In a normal system, the DPS value reads close to atmospheric pressure.

^ Canister Purge Valve Check (P0441) - The canister close valve closes for 4.5 seconds (grounded near zero volts) and the canister purge valve is closed (at battery voltage). In a normal system, the DPS shows a small rise in pressure from fuel vaporization of approximately 0.02 volts.

^ Large Leak Check (P0455) - This check occurs in 2 parts. Part 1 - The canister purge valve begins cycling (opening), and the canister close valve is initially open, and then closes. In a normal system, within 5 seconds after the purge control valve begins to cycle, the DPS must be drawn down at least 0.04 volts from atmospheric pressure. Part 2 - within 9 seconds after the purge control valve begins to cycle, the DPS voltage must drop more than 0.64 volts from atmospheric pressure.

^ Vacuum Stabilization Period - The DPS voltage should not continue to decrease 2 seconds after the purge control valve stops purging. A long stabilization period may not set a code immediately, however, it may eventually set a code.

^ Small Leak Check (P0442) - The system checks for small leaks for a period of five seconds after the DPS has reached its lowest voltage (maximum vacuum). The canister close valve is closed, and the canister purge valve is closed. In a normal system, the DPS voltage does not rise more than 0.17 volts during the five seconds before the canister close valve opens.

^ Recovery Period - The canister close valve opens and the canister purge valve remains closed. In a normal system, the voltage rises approximately 0.1 volt per second during the recovery period.





This is one example of a plot showing when a P0446 is set into the PCM. The self check appears as if it never took place.

Comments:
Electrically, the canister purge valve appeared normal. However, this vehicle had a canister purge valve that was "mechanically" open causing vacuum at the DPS sensor. This is only one example of a cause for P0446. Be sure to check all three circuits as described including the plastic tube in the frame rail for moisture and foreign material, and perform the self check to ensure the system works properly.





This is one example of a plot showing when a P0441 is set into the PCM. The self check shows only "half" of the self check.





This is one example of a plot showing where to check for Part 1 of the Large Leak (P0455) check.





This is one example of a plot showing where to check for Part 2 of the Large Leak (P0455) check.





This is one example of a plot showing the Small Leak (P0442) check.





GRAGH # 7 - Long Vacuum Stabilization





GRAPH # 8 - Slow Recovery Process After The Self Check





This is one example of a plot showing a slow recovery process.

This is an example of a plot showing when/where to "rev" the engine to perform another self check. If another self check occurs, the car is NOT fixed and will eventually set a DTC code. If the canister close valve remains at battery voltage for 30 seconds and another self check does not occur, then the system is fixed.

^ DPS voltage does not respond when vacuum is applied during the self check (P0455). The self check skips the P0442 check at point "A". The canister purge valve begins its "normal" purge cycle at point "B". The engine is "revved" at point "C". Since the system set a P0455 (this will work with a P0442 also), another self check occurs at point "D". This system needs to be repaired.

^ Canister Purge Valve appears to be cycling properly as shown in the waveform.

^ Canister Close Valve is "open" allowing fresh air into the system when HDS reads battery voltage.








The two graphs show how the fuel level of the vehicle affects the appearance of the self check. In both cases, the vehicle has passed the self check. Warm temperatures combined with low fuel in the tank increases the vapor pressure of the system (a high vapor pressure can cause the check to stop).

The above graph shows an Elantra with a FULL fuel tank with ambient temperature at 70°F (21°C).








The above graph shows the same Elantra vehicle as the previous graph, but with a near EMPTY fuel tank and ambient temperature at 70°F (21 °C).