Circuit Description
The vehicle control module (VCM) monitors the performance of the evaporative emissions (EVAP) system by applying a predetermined level of vacuum to the EVAP system and monitoring the vacuum decay rate. The VCM sets this DTC if the vacuum decay rate is more than a predetermined value. The VCM 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 VCM 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 VCM 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 relaease the vacuum in the EVAP system with the EVAP purge valve OFF and the EVAP vent valve OFF. This test indicates a blocked or restricted EVAP vent path if the EVAP system fails to release the vacuum quickly enough.
Conditions for Running the DTC
| • | No active manifold absolute pressure (MAP) sensor DTCs |
| • | No active throttle position (TP) sensor DTCs |
| • | No active vehicle speed sensor (VSS) DTCs |
| • | No active heated oxygen sensor (HO2S) DTCs |
| • | No active engine coolant temperature (ECT) sensor DTCs |
| • | No active intake air temperature (IAT) sensor DTCs |
| • | DTC P0125 is not active |
| • | The fuel level is more than 12.5 percent and less than 87 percent |
| • | The system voltage is 10 - 17 volts |
| • | The ECT is 4°C - 30°C (39°F - 86°F) |
| • | The IAT is 4°C - 30°C (39°F - 86°F) |
| • | The cold start ECT minus IAT is less than the following: |
| 1.5°C when the IAT is more than the ECT or |
| 8°C when the ECT is more than the IAT |
| • | The barometric pressure (BARO) is more than 72 kPa |
| • | The change in the fuel tank vacuum is less than 0.6 inches of H2O, or the change in the fuel level is less than 8 percent |
| • | The fuel tank vacuum level remains more than a calibrated value for a specified number of seconds |
Conditions for Setting the DTC
The VCM fails to detect a drop in the EVAP system vacuum over a calibrated number of seconds with the vent valve open.
Action Taken When the DTC Sets
| • | The VCM illuminates the malfunction indicator lamp (MIL) during the first key cycle in which the DTC sets. |
| • | The VCM stores the conditions that were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
Important: An accurate indication of the fuel level is required for the VCM to properly pass or fail this DTC. Always diagnose any fuel level sensor DTCs before performing this diagnostic. Always check for fuel level sensor DTCs stored in History.
Check for the following conditions:
| • | A missing, damaged, incorrect or improperly installed fuel cap |
| • | Any missing or damaged O-rings at the EVAP canister fuel vapor and purge line fittings |
| • | A cracked or punctured EVAP canister |
| • | Any incorrectly routed or damaged EVAP system purge and vapor lines |
| • | A damaged or disconnected EVAP purge line, vent hose, or fuel tank vapor line |
| • | A stuck-closed EVAP vent valve |
| • | A restricted or stuck-closed fuel tank rollover valve |
| • | A poor connection at the VCM. Inspect the harness connectors for the following conditions: |
| - | Any backed-out terminals |
| - | Any improper mating |
| - | Any broken locks |
| - | Any improperly formed or damaged terminals |
| - | Any poor terminal-to-wire connections |
| • | A damaged harness. Inspect the wiring harness to the EVAP vent valve, the EVAP purge valve, and the fuel tank pressure sensor for an intermittent, an open, or a short circuit |
| • | A kinked, pinched, or plugged EVAP purge, or fuel tank vapor line. Verify that the lines are not restricted. |
Refer to Evaporative Emission System Cleaning before starting repairs.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers 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.
-
Checks the vapor canister and the EVAP vent valve for restriction.
-
An EVAP pressure sensor that does not correctly respond to pressure will cause this DTC to set. The EVAP pressure sensor monitors a range from 7.5 inches H2O of pressure to -17.5 inches H2O of pressure. 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 reading on the diagnostic cart to the EVAP pressure sensor reading on the scan tool.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: : Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module data is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | Inspect the EVAP system for the following conditions:
Repair the EVAP system if necessary. Was a repair made to the EVAP system? | -- | ||
3 | Are DTCs P0452 or P0453 also set? | -- | ||
Does the EVAP fuel tank pressure quickly drop to near 0 inches H2O when 0% EVAP Purge is commanded and the EVAP vent valve is opened? | -8 in H2O | Go to Diagnostic Aids. | ||
Does the vacuum decrease from the specified value when the EVAP vent valve is opened? | 5 in. Hg | |||
6 |
Does the vacuum decrease from the specified value when the vent line is unplugged? | 5 in. Hg | ||
7 |
Was the EVAP vent line replaced? | -- | ||
8 |
Was the fuel tank vapor line replaced? | -- | ||
|
Important: The following steps require the J 41413 EVAP pressure/purge diagnostic station. Always zero the EVAP pressure and vacuum gauges on the EVAP pressure/purge diagnostic station before proceeding with diagnosis.
Do both values indicate the same amount of vacuum in the EVAP system to within the range specified? | +/ - 2 in H2O | |||
10 |
Does the test lamp illuminate? | -- | ||
11 | Check for a short to ground on the driver circuit of the EVAP vent valve . Repair circuit as necessary. Was a problem found? | -- | ||
12 | Replace the EVAP vent valve. Refer to Evaporative Emission Vent Valve Replacement . Is the replacement complete? | -- | -- | |
13 | Replace the EVAP vapor canister. Refer to Evaporative Emission Canister Replacement . Is the replacement complete? | -- | -- | |
14 | Replace the EVAP fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the replacement complete? | -- | -- | |
15 |
Important: : The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete. | -- | -- | |
16 |
Does the scan tool indicate the diagnostic Passed? | -- | -- | |
17 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
