Diagnostic Instructions

DTC Descriptor

DTC P2401: Evaporative Emission (EVAP) System Leak Detection Pump Control Circuit Low Voltage

DTC P2402: Evaporative Emission (EVAP) System Leak Detection Pump Control Circuit High Voltage

Diagnostic Fault Information

Component	Cause	DTCs
EVAP Vent Solenoid Valve	Always ON	P043E, P043F, P2401, P2402, P2419
EVAP Vacuum Leak Pump	•  Always ON     •  Always OFF	P043E, P043F, P2401, P2402, P2419
EVAP Canister Assembly	0.02 Inch Reference Orifice Blocked or Restricted	P043E, P043F, P2401, P2402, P2419
	0.02 Inch Reference Orifice High Flow	P043E, P043F

Circuit/System Description

The diagnostic strategy for the evaporative emission (EVAP) system uses a vacuum pump to test for system leaks, after the engine is OFF. A unique fuel tank, EVAP canister, and EVAP vacuum leak pump work together to provide enhanced system diagnosis. The vacuum leak pump, the fuel tank pressure (FTP) sensor and the EVAP canister vent valve are all integral parts of one assembly. The assembly is attached directly to the EVAP canister, located near the fuel tank.

After the vehicle has sat with the engine OFF for greater than 5 hours and the engine coolant temperature is less than 35°C (95°F), a comprehensive diagnostic is enabled. The complete diagnostic test can take up to 15 minutes to run, with leak detection comprising the largest portion of the test.

The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves.

Control Module Command	EVAP Canister Purge Valve	EVAP Canister Vent Valve
ON	Open	Closed
OFF	Closed	Open

Conditions for Running the DTC

Conditions for Setting the DTC

P2401

The powertrain control module (PCM) has determined the EVAP vacuum leak detection pump may be stuck OFF, because the specified vacuum pressure was not obtained.

P2402

The powertrain control module (PCM) has determined the EVAP vacuum leak detection pump may be stuck ON, because the vacuum pressure was greater than expected.

Action Taken When the DTC Sets

DTC P2401 and P2402 are Type B DTCs.

Conditions for Clearing the DTC

DTC P2401 and 2402 are Type B DTCs.

Diagnostic Aids

Low fuel levels in the fuel tank can affect the accuracy of the Service Bay Test. Fill the fuel tank to between one half and three quarters and retest.

Reference Information

Schematic Reference

Engine Controls Schematics

Description and Operation

Evaporative Emission Control System Description

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

With Service Bay Test

1. Verify the EVAP system using the EVAP Service Bay Test, refer to Service Bay Test. DTC P2401 or P2402 should not set.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Without Service Bay Test

Important: 

•	Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. Small changes in fuel tank pressure are difficult to detect with high fuel temperatures.

•	Low fuel levels in the fuel tank can affect the accuracy of fuel tank pressure readings. Small changes in fuel tank pressure are detected sooner when the fuel level is between one half and three quarters of a tank.

1. Engine running, observe the scan tool FTP sensor voltage parameter. Command the EVAP vacuum leak pump ON and OFF several times with the scan tool. The FTP sensor voltage should decrease slightly when the pump is activated.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the EVAP vacuum leak pump assembly.
2. Ignition OFF, test for less than 10 ohms between the EVAP vacuum leak pump ground circuit terminal 6 and ground G104.

⇒	If greater than the specified range, test the signal low circuit for an open/high resistance. If the circuit tests normal, replace the PCM.

3. Connect a test lamp between the EVAP vacuum leak pump control circuit terminal 1 and ground.
4. Ignition ON, command the EVAP vacuum leak pump ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp does not illuminate, test the leak pump control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the EVAP vacuum leak pump.

5. Connect the EVAP vacuum leak pump electrical connector.

Important: 

•	Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. Small changes in fuel tank pressure are difficult to detect with high fuel temperatures.

•	Low fuel levels in the fuel tank can affect the accuracy of fuel tank pressure readings. Small changes in fuel tank pressure are detected sooner when the fuel level is between one half and three quarters of a tank.

6. Engine running, observe the scan tool FTP sensor voltage parameter. Command the EVAP vacuum leak pump ON and OFF several times with the scan tool. Verify the FTP sensor voltage parameter decreases 0.10-0.20 volts when the pump is activated.

⇒	If less than the specified range, replace the EVAP vacuum leak pump assembly.

Repair Instructions

Repair Verification

With Service Bay Test

Verify the EVAP system repair using the EVAP Service Bay Test.

Without Service Bay Test

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.