Evaporative System - Leak Detection DTC Diagnosis: Overview
NO.: TSB-98-13-012DATE: September, 1998
MODEL: 1996-97 Eclipse 2.0L Non-Turbo
SUBJECT:
EVAPORATIVE EMISSION CONTROL LEAK DETECTION SYSTEM DIAGNOSIS
PURPOSE
This bulletin describes the operation of the evaporative emission control leak detection system and how to diagnose diagnostic trouble codes (DTCs) relevant to this system (DTCs 183, 184, 187, 160, and 161).
The table lists the topics covered in this bulletin and their corresponding page numbers.
It is very important to read and understand the information before attempting diagnosis.
AFFECTED VEHICLES
1996-97 Eclipse models equipped with 2.0L non-turbocharged (420A) engine
INTRODUCTION
The evaporative emission system is designed to prevent the escape of fuel vapors from the fuel system. Any leaks in the system, even small ones, can allow fuel vapors to escape into the atmosphere, adding to air pollution. Government regulations require auto manufacturers to have onboard testing to make sure the evaporative system is functioning properly.
The leak detection system used on 2.0L non-turbo Eclipse models tests for EVAP system leaks and blockage, and also performs self-diagnostics. To perform the test, the powertrain control module (PCM) first checks the leak detection pump (LDP) for electrical and mechanical faults. If it passes, the PCM then uses the LDP to seal the evaporative emission system vent and pump air into the system to pressurize it. If there is a leak in the system, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the size of the leak based on how fast it must pump the LDP as it tries to maintain pressure in the system.
EVAP LEAK DETECTION SYSTEM COMPONENTS
Service Vacuum Supply Tee (SVST) - The SVST is a one-way valve which provides a test port for applying vacuum to the LDP. This allows vacuum to be applied to the LDP without losing vacuum to the intake manifold. Vacuum must be applied to help seal the LDP for testing.
Service Port - Allows application of pressure to the system and monitoring of the system pressure during testing.
EVAP Purge Solenoid - The PCM uses the EVAP purge solenoid to control purging of excess fuel vapors stored in the system. It remains closed during leak testing to prevent loss of pressure. A leak could occur if the EVAP purge solenoid fails by sticking open.
EVAP Canister - Controlled by the PCM, the EVAP canister stores excess fuel vapors from the fuel tank for purging.
EVAP Purge Orifice - Limits purge volume.
EVAP System Air Filter - Provides fresh air to the LDP for pressurizing the system. It filters out dirt while allowing a vent to atmosphere for the EVAP system.
Leak Detection Pump (LDP) - The LDP performs several functions. It closes the EVAP system vent to atmospheric pressure (through the air filter) so the system can be pressurized for leak testing. Powered by engine vacuum, it pumps air into the EVAP system to develop a pressure of about 0.25 (1/4) psi. A switch in the LDP allows the PCM to monitor the position of the LDP diaphragm. Using the LDP switch input, the PCM is able to monitor how fast the LDP is pumping air into the EVAP system, which allows detection of leaks and blockage.
The LDP assembly consists of several parts. The solenoid is controlled by the PCM, and connects the pump cavity to either vacuum or atmospheric pressure (through a small air filter). A vent valve closes the EVAP system vent to atmosphere, sealing the system during leak testing. The pump section of the LDP consists of a diaphragm that moves up and down to draw air in through an air filter and inlet check value, and pump it out through an outlet check value. The diaphragm is pulled up by engine vacuum, and pushed down by a spring, as the LDP solenoid turns on and off. The LDP also has a magnetic reed switch to signal diaphragm position to the PCM. When the diaphragm is down, the switch is on, which sends a 12 V (system voltage) signal to the PCM. When the diaphragm is up, the switch is off, and there is no voltage sent to the PCM. This allows the PCM to monitor LDP pumping action as it turns the LDP solenoid on and off.
When the LDP is at rest, with no pressure or vacuum present, the diaphragm is forced down by the spring pushing on it. The LDP solenoid is blocking engine vacuum, and is open to atmospheric pressure from the EVAP system air filter. The vent valve is held open by the diaphragm, which allows the canister to vent to the atmosphere.
When the PCM energizes the LDP solenoid, the solenoid blocks the hose leading to the EVAP air filter and, at the same time, connects engine vacuum to the pump cavity above the diaphragm. The vacuum above the diaphragm causes it to move up and draw air in through the EVAP air filter and inlet check valve. When the diaphragm completes its upward movement, the LDP switch turns from on to off.
Next, the PCM de-energizes the LDP solenoid, so it blocks engine vacuum and vents the upper pump cavity through the EVAP air filter to the atmosphere. The spring is now able to push the diaphragm down, which pumps air out through the outlet check valve. The LDP switch turns from oft to on, which allows the PCM to monitor LDP pumping activity.
As the solenoid is turned on and off, the cycle is repeated and the EVAP system is pressurized by the LDP pumping action. During portions of the EVAP Leak Detection Test, the PCM uses the LDP switch to monitor diaphragm movement. The solenoid is only turned on by the PCM after the LDP switch changes from off to on, indicating that the diaphragm has moved down. At other times during the EVAP Leak Detection Test, the PCM rapidly cycles the LDP solenoid on and oft to quickly pressurize the system. The diaphragm does not move enough during this rapid cycling to turn the switch on and off, so the PCM uses a fixed time interval to cycle the solenoid. The EVAP Leak Detection Test Sequence in this bulletin details LDP operation during the test.
If the system does not pass the EVAP Leak Detection Test, the following DTCs may be set:
^ DTC 183 (P1495) - LDP Solenoid Electrical Malfunction
^ DTC 184 (P1494) - LDP Position Switch or Mechanical Fault
^ DTC 187 (P1486) - Evaporative Emission Control System Blockage Detected
^ DTC 160 (P0442) - Evaporative Emission Control System Small Leak Detected DTC 161 (P0455) - Evaporative Emission Control System Large Leak Detected
ENABLING CONDITIONS TO RUN EVAP LEAK DETECTION TEST (As displayed on MUT-II data list).
^ Cold start:
- "Battery" temperature (obtained from a temperature sensor inside the PCM) between 4°C (40°F) and 31°C (890°F). On MUT-II data list, "BATTERY TEMP 45".
- Engine coolant temperature within +/- 5.6°C (10°F) of "battery" temperature. On MUT-II data list, "ENG CLNT TEMP OS".
^ Battery voltage 10-15 volts
NOTE:
If battery voltage momentarily drops below 10 volts during engine cranking, the EVAP Leak Detection Test will not run.
^ Low fuel warning light off - On MUT-II data list "LOW FUEL LEVEL SN 78" reading is below 2000 mV
^ MAP sensor reading 22 inHg or above (This is the manifold absolute pressure, not vacuum.) - On MUT-II data list "MAP SENSOR 11"
^ No engine stall during test
^ The following DTCs must not be set:
- DTC 18 Purge solenoid electrical fault
- DTC 02 - PCM self-test faults
- DTC 01 - Cam sensor faults
- DTC 40 - Crank sensor faults
- DTC 132, DTC 26 - TPS faults
- DTC 30, DTC 31 - Coolant sensor faults
- DTC 36, DTC 37, DTC 39, DTC 135 - MAP sensor faults
- DTC 71, DTC 153, DTC 154 - Battery temperature sensor electrical faults
When the ignition key is turned to ON, the LDP diaphragm is normally down and the LDP switch is on. If the EVAP system has residual pressure from the previous drive because purging did not take place, the LDP diaphragm may be up. This could result in the LDP switch being off when the key is turned to ON.
After the key is turned on, the PCM immediately tests the LDP solenoid circuit for electrical faults. If a fault is detected, DTC 183 (P1495) is set, the MIL is illuminated, and the EVAP Leak Detection Test is canceled.
NOTE:
If the "battery" temperature is not within the required range to run the EVAP Leak Detection Test, or if the engine coolant temperature is not within 10 degrees of "battery" temperature, the PCM will not run tests for DTC 184, DTC 187, DTC 160, and DTC 161.
If DTC 183 is not set, the PCM checks for DTC 184 (P1494). If the LDP switch was on when the key was turned to ON, the PCM energizes the LDP solenoid for two seconds and monitors the LDP switch. As the LDP diaphragm is pulled up by engine vacuum, the LDP switch should change from on to off. If it does not, the PCM sets a temporary fault in memory, and waits until the next time the Enabling Conditions are met to run the test again. If the problem is again detected, DTC 184 is stored and the MIL is illuminated. If the problem is not detected, the temporary fault will be cleared.
However, if the PCM detects that the LDP switch is off when the key is turned to ON, the PCM must determine whether this condition is due to residual pressure in the EVAP system from the last drive, or an actual fault. The PCM stores information in memory on EVAP system purging during the previous drive.
^ If little or no purging took place, residual pressure could be holding the LDP diaphragm up, causing the LDP switch to be off. Since this is not a malfunction, the PCM cancels the EVAP Leak Detection Test, but does not set a temporary fault.
^ If there was sufficient purging on the previous drive to eliminate EVAP system pressure, the PCM judges that this is a malfunction and sets a temporary fault in memory. The next time that the Enabling Conditions are met, the test will run again. If the fault is again detected, the MIL will illuminate and DTC 184 will be stored. If the fault is not detected, the temporary fault will be cleared.
If no fault has been detected so far, the PCM begins testing for a possible blockage in the EVAP system between the LDP and the fuel tank. This is done by monitoring the time required for the LDP to pump air into the EVAP system during three pump cycles. If no blockage is present, the LDP diaphragm is able to quickly pump air out of the LDP each time the PCM turns off the LDP solenoid. If a blockage is present, the PCM detects that the LDP takes longer to complete each pump cycle. If the three pump cycles take longer than 4 seconds, the PCM suspects a blockage. To confirm the blockage, the PCM monitors purge activity later in the drive. If a blockage is present, purge will also be affected, and the PCM will store a temporary fault in memory. On the next drive when Enabling Conditions are met, the test will run again. If blockage is again detected, DTC 187 (P1486) is stored, and the MIL is illuminated.
After the LDP test cycles for blockage are completed, the PCM then tests for EVAP system leakage. If the three LDP test cycles are completed in the normal period of time (about four seconds), the PCM then rapidly pumps the LDP for 70 cycles (about 43 seconds) to rapidly build pressure in the EVAP system. The LDP switch does not turn on and off during the rapid pumping because the diaphragm is not traveling through its full range during this part of the test.
Next, the PCM performs one or more test cycles by monitoring the time required for the LDP switch to turn on after the LDP solenoid is turned off.
^ If the switch does not come on, or comes on after a long delay, it means that the system does not have any significant leakage and the EVAP Leak Detection Test is complete.
^ However, if the LDP switch comes on quickly, there may be a leak, or the fuel level may be low enough that the LDP must pump more to finish pressurizing the EVAP system. The PCM will then rapidly pump the LDP again to build pressure in the EVAP system, and follow that by monitoring the time needed for several LDP test cycles. This process of rapid pumping followed by several LDP test cycles may repeat several times before the PCM judges that a leak is present.
When leaks are present, the LDP pump cycle time is proportional to the size of the leak. The larger the leak, the shorter the cycle time. The small the leak, the longer the cycle time. DTCs may be set when a leak as small as 1 mm (0.040") is present.
^ If the average pump cycle time is less than 0.8 seconds, a temporary fault is stored in PCM memory for a large leak (greater than 2.0 mm).
^ If the pump cycle time is between 0.8 and 1.8 seconds, a temporary fault for a small leak (1.0 - 2.0 mm) is stored in the PCM.
^ Leakage is considered insignificant (less than 1.0 mm) when the pump cycle time is over 1.8 seconds.
If a leak is detected again the next time the EVAP Leak Detection Test runs, the MIL will illuminate and DTC 160 (P0442) will be stored for a small leak or DTC 161 (P0455) will be stored for a large leak. If no leak is detected during the next test after a temporary fault was set, the temporary fault will be cleared.
TIP: During diagnosis, you can compare the LDP solenoid activity with the monitor sequence in the chart. (Refer to "EVAP Leak Detection Test Tips" of this bulletin.) If the PCM detects a problem that could set a DTC, the testing is halted and LDP solenoid activity stops. As each section of the test runs, this indicates that the previous section passed successfully. By watching to see which tests complete, you can see if any conditions are present that the PCM considers abnormal. For example, if the LDP solenoid is energized for the three test cycles to test for blockage (DTC 187), this means that the LDP has already passed its test (DTC 184). Then, if the PCM detects a possible blockage, it will set a temporary fault without turning on the MIL and continue the leak portion of the test. However, the PCM will assume that the system is already pressurized and skip the 70 rapid pump cycles.
This bulletin contain detailed instructions for troubleshooting individual DTCs.
IMPORTANT
Be sure that the PCM has the latest software update. Reprogram as necessary.
After repairs or parts replacement, the Readiness Test must be successfully completed before returning the vehicle to the customer.
PARTS INFORMATION
WARRANTY INFORMATION
IMPORTANT:
^ The following labor operations apply only to the procedures described in this bulletin.
^ If the vehicle is not repaired after 2.0 hours diagnosis time, contact Tech Line before proceeding. Claims for diagnosis time over 2.0 hours must have a Tech Line call number noted on the warranty claim.
^ These repairs are on a customer complaint basis only.
^ DTCs must be recorded on the claim.
^ 5 years/50,000 miles Emissions warranty coverage applies.
DTC 183 (LDP Solenoid Electrical Malfunction) Diagnosis
Labor Operation No. 1786TBA1 Time Allowance: 0.7 hr.
DTC 184 (LDP Position Switch or Mechanical Fault) Diagnosis
Labor Operation No. 1786TBA2 Time Allowance: 0.5 hr.
DTC 187 (Evaporative Emission Control System Blockage) Diagnosis
Labor Operation No. 1731TBA1 Time Allowance: 0.7 hr.
DTC 160/161 (Evaporative Emission Control System Leak) Diagnosis
Labor Operation No. 1731TBA2 Time Allowance: 1.0 hr.
Readiness Test (Includes test drive)
Labor Operation No. 1731TBA3 Time Allowance: 0.5 hr.