DTC P0446 Evaporative Emission (EVAP) Vent System Performance. Cadillac DeVille 1999

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1999 🢒 DeVille 🢒 DTC 🢒 DTC P0446 Evaporative Emission (EVAP) Vent System Performance

Engine Controls Components
Cell 20: MAF Sensor, EVAP Components and EGR Valve
OBD II Symbol Description Notice
ESD Notice

Circuit Description

The PCM tests the EVAP system for the following conditions:

•	Large and small leaks (P0440 and P0442)

•	Excess vacuum (P0446)

•	Purge flow during non-commanded conditions (P1441)

•	Fuel Pressure sensor and Fuel Level sensor faults (P0452, P0453, P0461, P0462 and P0463)

•	EVAP Purge and Vent Valve faults (P1645 and P1646)

The PCM monitors the amount of vacuum and the amount of pressure in the EVAP system by monitoring the Fuel Tank Pressure sensor. For this DTC the PCM turns ON both the EVAP Purge Valve and the EVAP Vent Valve when the Conditions for Running the DTC are met. This applies an engine vacuum to a closed EVAP system. The PCM turns OFF both the EVAP Purge Valve and the EVAP Vent Valve when the system reaches a correct amount of vacuum. The EVAP system should quickly RELEASE the vacuum in the EVAP system with the EVAP Purge Valve OFF and the EVAP Vent Valve OFF (open). This test indicates a blocked or restricted EVAP Vent Valve or path if the EVAP system fails to release the vacuum quickly enough. This DTC will set after two consecutive failures of the above test.

Conditions for Running the DTC

•	DTC's P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0141, P0151, P0152, P0153, P0154, P0452, P0453, P0503, P1111, P1112, P1114, P1115, P1133 or P1153 are not set.

•	Battery voltage is between 10.5 and 17.5 volts.

•	Barometric pressure is more than 71.78 kPa.

•	Fuel level is between 10% and 89.8% of full capacity for at least 3.2 seconds continuously. The time limit is required because fuel sloshing within the tank may cause the fuel level indication to vary outside the fuel level limits.

•	Coolant temperature is between 2°C and 32.7°C.

•	Intake air temperature is between 2°C and 32.7°C

•	Start up coolant and intake air temperature are within 14.2°C of each other.

Conditions for Setting the DTC

•	The EVAP system fails to vent vacuum at a quick enough rate.

•	There is too much system vacuum present at the start of this test.

Important: This DTC does NOT report a first failed test. A first fail of this DTC will have a scan tool status as Not Run. Use the scan tool data display parameter of EVAP TEST RESULT to determine if this DTC has failed or passed for THIS ignition cycle.

Action Taken When the DTC Sets

•	The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails.

•	The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records.

•	A first failure of this DTC will NOT store as Last Test Failed or History.

Conditions for Clearing the MIL/DTC

•	The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

•	A Last Test Failed DTC will clear when the diagnostic runs and does not fail.

•	A History DTC will clear after forty consecutive warm-up cycles with no failures of any diagnostic test.

•	Use a scan tool to clear DTCs.

•	Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module Description .

Diagnostic Aids

Important: An accurate indication of fuel level is required for the PCM to properly Pass or Fail this DTC. Always diagnose fuel level sensor DTC's before performing this DTC's diagnostic table. Always check for fuel level sensor DTC's stored as History.

Perform a physical inspection of the EVAP system. Check for the following conditions:

•	A loose, missing, defective, or incorrect fuel tank cap

•	Incorrectly routed or defective EVAP system vacuum and vapor lines

•	A stuck closed EVAP Vent Valve

•	A restricted or blocked EVAP system hose

•	A restricted or stuck closed fuel tank rollover valves

•	A malfunctioning or damaged vapor canister

Check for charcoal release from the vapor canister. Refer to Evaporative Emission System Cleaning .

If the vehicle had a P1441 stored and set a P0446 while performing the Service Bay Test inspect the EVAP Solenoid Purge Valve for Flow During Non-Purge (leakage).

The vacuum and pressure in the EVAP system is measured in inches of water (H2O). Most gauges measure vacuum in inches of mercury (Hg) and pressure in pounds per square inch (psi). The following shows how the values compare:

in H2O	in Hg	psi
1in H2O	0.07 in Hg	0.0361 psi
5 in H2O	0.36 in Hg	0.180 psi
10 in H2O	0.73 in Hg	0.361 psi
15 in H2O	1.10 in Hg	0.541 psi

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

If the vacuum stored in the EVAP system is quickly released then an intermittent system restriction or failure of the EVAP Vent Valve or the EVAP Fuel Tank Pressure Sensor may have occurred.

Checking the vapor canister and the EVAP Vent Valve for restriction.

An EVAP Pressure sensor that does not correctly respond to pressure (or vacuum) will cause this DTC to set.

The EVAP Pressure Sensor monitors a range from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).

In order to test the EVAP Pressure sensor for pressure response SEAL the system with the scan tool and use the EVAP pressure/purge diagnostic cart to apply pressure to the system. Compare the pressure gauge (in. H2O) on the diagnostic cart to the EVAP Pressure sensor reading on the scan tool.

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Inspect the EVAP system for the following conditions:

•	Improperly routed, kinked or damaged EVAP purge and tank vent lines.

•	A damaged EVAP system component.

Repair the EVAP system if needed.

Was a repair made to the EVAP system?

Go to Powertrain Control Module Diagnosis

Go to Step 3

Turn the key OFF.
Remove the fuel cap.
Wait 30 seconds.
Replace the fuel cap.
Turn the key ON but DO NOT start the engine.
Using the scan tool monitor the EVAP Fuel Tank Pressure sensor display.

Is the value displayed the same or less than the value specified?

0 in. H2O

Go to Step 4

Go to Step 10

Start and idle the engine.
Using the scan tool select the EVAP Purge/Seal function.
While monitoring the EVAP Fuel Tank Pressure sensor display, command enough EVAP Purge to obtain -5 in H2O.
After the specified value has been obtained SEAL the system.
While monitoring the EVAP Fuel Tank Pressure sensor display, command the EVAP Vent Valve OPEN (press exit).

Does the EVAP Fuel Tank Pressure sensor drop to the specified value when 0% EVAP Purge is commanded and the EVAP Vent Valve is opened?

0 in. H2O

Fault not present.

Go to Step 5

Turn the ignition OFF.
Disconnect the fuel tank vapor and the EVAP purge lines from the EVAP vapor canister.
Plug the CANISTER fitting for the fuel tank vapor line.
Connect a hand vacuum pump to the EVAP purge line canister fitting.
With the ignition ON, engine OFF, command the EVAP Vent Valve ON (closed).
Using the hand vacuum pump apply and hold the specified amount of vacuum.
While monitoring the hand vacuum pump gauge command the EVAP Vent Valve OFF (open).

Does the vacuum drop from the specified value when the EVAP Vent Valve is opened?

5 in. Hg.

Go to Step 8

Go to Step 6

Leave system as connected in Step 5.
Disconnect the vent line at the EVAP Vent Valve.
Plug the vent line.
Using the hand vacuum pump apply and hold the specified amount of vacuum.
While monitoring the hand vacuum pump gauge remove the plug from the vent line.

Does the vacuum drop from the specified value when the vent line is unplugged?

5 in. Hg.

Go to Step 11

Go to Step 7

Inspect the EVAP Vent line from the canister to the EVAP Vent Valve for restrictions.
Replace the vent line if needed.

Was the EVAP Vent line replaced?

Go to Powertrain Control Module Diagnosis

Go to Step 12

Check the fuel tank vapor line for a restriction.
Replace the vapor line if needed.

Was the fuel tank vapor line replaced?

Go to Powertrain Control Module Diagnosis

Go to Step 9

Important: The following steps require the EVAP pressure/purge diagnostic station J 41413.

Always zero the EVAP Pressure and Vacuum (in. H2O) gauges on the EVAP pressure/purge diagnostic station before proceeding with diagnosis.

Turn the ignition OFF.
Remove the plug and the hand held vacuum pump.
Reconnect the EVAP vapor canister purge and vent lines.
Connect the EVAP pressure/purge diagnostic station to the EVAP system service port.
Operate the vehicle until the EVAP Purge Solenoid Valve can be commanded ON with a scan tool.
Using the scan tool, use Purge/Seal to turn the EVAP Purge Solenoid Valve ON to varying vacuum levels with the engine running and quickly SEAL the system with the scan tool. Leaving the EVAP Purge Solenoid Valve ON for higher percents or longer times will allow a higher amount of vacuum to develop. A maximum of -14 in. H2O of vacuum can be applied to the EVAP system using the scan tool.
While the system is sealed compare the EVAP pressure/purge diagnostic stations vacuum gauge (in. H2O) to the vacuum shown on the scan tool from the EVAP Fuel Tank Pressure sensor. Allow a few seconds for the system to stabilize.

Do both values indicate the same amount of vacuum in the EVAP system to within the range specified?

+ or - 2 in. H2O

Go to Step 2

Go to Step 13

Turn the key OFF.
Disconnect the EVAP Fuel Tank Pressure sensor connector.
Disconnect PCM connector C1.
Using DMM J 39200 measure the resistance of the sensor ground circuit between the PCM connector and the EVAP Fuel Tank Pressure sensor connector.

Is the resistance the same or less than the value specified?

5 ohms

Go to Step 13

Go to Step 14

Replace the EVAP Vent Valve.

Is the replacement complete?

Go to Powertrain Control Module Diagnosis

Replace the EVAP Vapor Canister.

Is the replacement complete?

Go to Powertrain Control Module Diagnosis

Replace the EVAP Fuel Tank Pressure sensor.

Is the replacement complete?

Go to Powertrain Control Module Diagnosis

Repair the open EVAP Fuel Tank Pressure sensor ground circuit. Is the repair complete?

Go to Powertrain Control Module Diagnosis