Tech Tips (TIPS_SE_JULY2022)

TECH TIPS

TECHNICAL INFORMATION TIPS

SERVICE INFORMATION

SPECIAL EDITION 

2012-Current Model Subaru Evaporative Diagnostics & Smoke Testing 

When faced with an Evaporative Emissions DTC (P0441-P0459, P2404 etc.), the first thing most Technicians do is reach for the smoke machine to check for leaks.

This should no longer be a Technicians first step for diagnosis  .

Never put pressure into the ELCM or use smoke as residual oil in the smoke can contaminate the ELCM and cause internal  components to malfunction.

Instead, the first step for diagnosis should be a forced self-test of the evaporative emission system, recording the test results, then graphing the test to determine where the problem is.

Late model Subaru vehicles are equipped with an Electronic Leak Check Module (ELCM) in their evaporative system. The ELCM is a very sensitive and delicate piece of electronic equipment that has the capability of performing self-tests to inspect the systems integrity for leaks and operation.

These systems operate on vacuum, not pressure  , when performing their self-test.

Follow the outlined directions in this document for performing the ELCM forced self-test, then use the diagnosis procedure found in STIS to identify where the problem is. Technicians can graph the recorded self test and compare it to the diagnosis chart. This chart is in the General Description tab or located at the bottom of most Evap DTC Trouble Trees in STIS. This article also includes a reference chart, along with examples of completed graphs with a set DTC. The Subaru smoke machine tool kit comes with the correct quick disconnect plugs to be able to block off the disconnected lines. Below are step-by-step directions for performing the ELCM force test, saving that test data and using it to diagnose the concern.

2013MY to Current Legacy and Outback

2012MY to Current Impreza

2013MY to Current XV Crosstrek

2014MY to Current Forester

2013MY-2014MY Tribeca

2015MY to Current WRX

2013MY to Current BRZ

2019MY to Current Ascent

OVERVIEW OF EVAPORATIVE SYSTEM

• The ELCM is a device installed in the evaporative system to detect leaks and blockages.
• According to legal regulations, leaks of 0.02 inch or more need to be detectable.

SUMMARY OF EVAP LEAK DIAGNOSIS

• EVAP Leak diagnosis is conducted during soak (5~7h after engine stop).
• The ELCM draws a vacuum in the Evaporative line and determines the leak by the level of negative pressure. 

To find a 0.02-inch leak, the ELCM measures two types of pressure:

1. Reference pressure  : pressure at the occurrence of a 0.02-inch leak
2. Tank pressure:  pressure in the EVAP line

   While measuring pressures 1) and 2), a P code is established according to the location of the abnormality.

The conditions needed to perform the test are as follows:

Vehicle	Model Year	Engine Coolant Temperature		Engine Oil Temp	Intake Air Temp	Battery Voltage
		F°	F°	F°	F°	V
Impreza/Crosstrek	13MY - 22MY	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9
Outback/Legacy	15MY - 22MY	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9
Forester	14MY - 22MY	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9
Ascent	ALL	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9
WRX	15MY - 22MY	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9
BRZ	13MY - 20MY	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9
	22MY	≥ 40	< 95	≥ 40	≥ 40	≥ 10.9
Tribeca	13MY-14MY	≥ 40	< 113	≥ 40	≥ 40	≥ 10.9

From the SSM4 Menu: 

Technicians will now be able to watch the test as it is being performed.

As the test runs, it will perform different phases.

Phase	Explaination of Phase	Diagnosis period
A	Vacuum pump operation confirmation and characteristics stability	7 s or less
B	Measurement of reference pressure for setting the target negative pressure	350 s or less
C	Switching valve operation confirmation	12 s or less
D	0.04 inch leak pressure measurement	900 s or less
	0.02 inch leak pressure measurement
	Clogging of pipe diagnosis and leak pressure measurement
E	Reference pressure measurement for judgment	50 s or less

Phase A 

The ECM uses this phase to check the operation of the vacuum pump.

The ECM simulates a 0.02 leak by using the reference pressure as the vacuum pump is running.

The switching valve is in the 'open' position. This allows ambient air to enter the ELCM.

Phase B 

The ECM measures the pressure and calculates the limit of negative pressure based on the reference.

Phase C 

The switching valve closes, and ECM measures the evaporative side pressure. The jump in pressure is caused by the movement of the switching valve. This also seals the system from ambient air.

Phase D 

With the switching valve closed, the ECM measures the pressure in the EVAP system in relation to the amount of time it takes to reach maximum vacuum.

Phase E 

The ECM measures the reference pressure again with the 0.02 simulated leak (ELCM orifice). During this phase, the ECM is determining the size of any leaks. Pressure during this phase is compared to pressure during phase B and should be very similar.

This is an example of a completed self-test, with "No DTC  " set after being performed:

This is an example of a completed self-test, with "P0455  " set after being performed:

This is an example of a completed self-test, with "P0456"  set after being performed:

This is an example of a completed self-test, with "P2404"  set after being performed: Evap System Absolute Pressure (Phase A) was not changed.

Evap System Absolute Pressure (Phase A) was too high.

Evap System Absolute Pressure (Phase A) was too low.

Above is a picture from STIS showing the basic outline for diagnosis in the ELCM force test. This will be useful in a comparison to the data graphed from the force test if a DTC is found.