EVAP Leak Detection Test Enabling Conditions
- Cold start with ambient temperature (obtained from modeling the inlet air temperature sensor) between 40°F (4°C) and 90°F (32°C) for 0.040" leak. Between 40°F (4°C) and 85°F (29°) for 0.020" leak.
- Engine coolant temperature is within 10 to 18° F (-8 to -12°C) of ambient.
- Battery voltage is between 10 and 15 volts.
- Low fuel warning light off (fuel level must be between 15 and 85 percent.
- MAP sensor reading is 22 in. Hg or above. This is the manifold absolute pressure, not vacuum.
- No engine stall during test.
Note. If battery voltage drops below 10 volts for more than 5 seconds during engine cranking, the EVAP leak detection test will not run
A DTC will not be set is a one trip fault is set or is the MIL is illuminated for any of the following
- Purge Solenoid Electrical Fault
- All TPS Faults
- All Engine Controller Self Test Faults
- LDP Pressure Switch Fault
- All Camshaft and/or Crankshaft Sensor Fault
- EGR Solenoid Electrical Fault
- All MAP Sensor Faults
- All Injector Faults
- Ambient Temperature Sensor Electrical Faults
- BARO Out of Range
- Vehicle Speed Faults
- All Coolant Sensor Faults
- LDP Solenoid Circuit
Note. If battery temperature is not within range, or if the engine coolant temperature is not within a specified range of the battery temperature, the PCM will not run tests for DTC P0441, P0442, P0455, P1486 or P1494. These temperature calibrations may be different between models.
Section 4 - No DTC Can Be Set During This Time
Section 4 refers to section 4 in the EVAP LDP Test Sequence. (Схема №36) After the LDP blockage tests are completed, the PCM then tests for EVAP system leakage. First, the PCM commands the LDP to rapidly pump for 20 to 50 seconds (depending on fuel level) to build pressure in the EVAP system. This evaluates the system to see if it can be sufficiently pressurized. This evaluation (rapid pump cycling) may occur several times prior to leak checking. The LDP reed switch does not close and open during rapid pumping because the diaphragm does not travel through its full range during this part of the test.
Section 5 - DTC P0456, P0442, P0455 EVAP Leak Monitor & Leak Detected
Section 5 refers to section 5 in the EVAP LDP Test Sequence. (Схема №36) Next, the PCM performs one or more test cycles by monitoring the time required for the LDP reed switch to close (diaphragm to drop) after the LDP solenoid is turned off. If the switch does not close, or closes 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 reed switch closes 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. In this case, the PCM will 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 1eak is present. When leaks are present, the LDP test cycle time will be inversely proportional to the size of the leak. The larger the leak, the shorter the test cycle time. The smaller the leak, the longer the test cycle time. DTCs may be set when a leak as small as.020" (0.5 mm) diameter is present. If the system detects a leak, a temporary fault will be stored in PCM memory. The time it takes to detect a.020",.040", or larger leak is based on calibrations that vary from model to model. The important point to remember is if a leak is again detected on the next EVAP Leak Detection Test, the MIL will illuminate and a DTC will be stored based on the size of leak detected. If no leak is detected during the next test, the temporary fault will be cleared.
Diagnostic Tips
During diagnosis, you can compare the LDP solenoid activity with the monitor sequence. (Схема №36) If the PCM detects a problem that could set a DTC, the testing is halted and LDP solenoid activity will stop. As each section of the test begins, it 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 test cycles to test for blockage (DTC P1486), it means that the LDP has already passed its test for DTC P1494. 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 rapid pump cycles. Always diagnose leaks, if possible, before disconnecting connections. Disconnecting connections may mask a leak condition. Keep in mind that if the purge solenoid seat is leaking, it could go undetected since the leak would end up in the intake manifold. Disconnect the purge solenoid at the manifold when leak checking. In addition, a pinched hose fault (DTC P1486) could set if the purge solenoid does not purge the fuel system properly (blocked seat). The purge solenoid must vent the fuel system prior to the LDP system test. If the purge solenoid cannot properly vent the system, the LDP cannot properly complete the test for DTC P1486 and this fault can set due to pressure being in the EVAP system during the test sequence. Multiple actuation's of the DRB III(R) Leak Detection Pump Monitor Test can hide a.020" leak because of excess vapor generation. Additionally, any source for additional vapor generation can hide a small leak in the EVAP system. Excess vapor generation can delay the fall of the LDP diaphragm thus hiding the small leak. An example of this condition could be bringing a cold vehicle into a warm shop for testing or high ambient temperatures. Fully plugged and partially plugged underhood vacuum lines have been known to set MIL conditions. DTCs P0456 and P1494 can be set for this reason. Always, thoroughly check hoses for pinches or blockage before condemning components.
Test Equipment
The Miller Evaporative Emission Leak Detector (8404) is capable of visually detecting leaks in the evaporative system and will take the place of the Ultrasonic Leak Detector (6917A). The EELD utilizes shop air and a smoke generator to visually detect leaks down to .020" or smaller. The food grade oil used to make the smoke includes an ultraviolet trace dye that will leave telltale signs of the leak under a Black light. This is helpful when components have to be removed to determine the exact leak location. For detailed test instructions, follow the operators manual packaged with the EELD.
ON-BOARD DIAGNOSTICS
The PCM has been programmed to monitor many different circuits of the fuel injection system. This monitoring is called on-board diagnosis. Certain criteria, or arming conditions, must be met for a trouble code to be entered into the PCM memory. The criteria may be a range of engine RPM, engine temperature, and/or input voltage to the PCM. If a problem is sensed with a monitored circuit, and all of the criteria or arming conditions are met, then a trouble code will be stored in the PCM. It is possible that a trouble code for a monitored a circuit may not be entered into the PCM memory even though a malfunction has occurred. This may happen because one of the trouble code criteria have not been met. The PCM compares input signal voltages from each input device with specifications (the established high and low limits of the range) that are programmed into it for that device. If the input voltage is not within specifications and other trouble code criteria are met, a trouble code will be stored in the PCM memory. The On Board Diagnostics have evolved to the second Generation of Diagnostics referred to as OBD-II. These OBD-II diagnostics control the functions necessary to meet the requirements of California OBD-II and Federal OBD regulation. These requirements specify the inclusion of a Malfunction Indicator Light (MIL). See MALFUNCTION INDICATOR LIGHT .
STATE DISPLAY TEST MODE
The switch inputs to the Powertrain Control Module (PCM) have two recognized states; HIGH and LOW. For this reason, the PCM cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the State Display screen shows the change from HIGH to LOW or LOW to HIGH, assume the entire switch circuit to the PCM functions properly. Connect the DRBIII(R) scan tool to the data link connector and access the State Display screen. Then access either State Display Inputs and Outputs or State Display Sensors.
CIRCUIT ACTUATION TEST MODE
The Circuit Actuation Test Mode checks for proper operation of output circuits or devices the Powertrain Control Module (PCM) may not internally recognize. The PCM attempts to activate these outputs and allow an observer to verify proper operation. Most of the tests provide an audible or visual indication of device operation (click of relay contacts, fuel spray, etc.). Except for intermittent conditions, if a device functions properly during testing, assume the device, its associated wiring, and driver circuit work correctly. Connect the DRBIII(R) scan tool to the data link connector and access the Actuators screen.
TEST SEQUENCE
In many instances, emissions systems must fail diagnostic tests more than once before the PCM illuminates the Malfunction Indicator Light (MIL). These tests are know as "two-trip monitors". Other tests that turn the MIL on after a single failure are known as "one-trip monitors". A trip is defined as start the vehicle and operate it to meet the criteria necessary to run the given monitor. Many of the diagnostic tests must be performed under certain operating conditions. However, there are times when tests cannot be run because another test is in progress (conflict), another test has failed (pending) or the Task Manager has set a fault that may cause a failure of the test (suspend).
- Pending Under some situations the Task Manager will not run a monitor if the MIL is illuminated and a fault is stored from another monitor. In these situations, the Task Manager postpones monitors pending resolution of the original fault. The Task Manager does not run the test until the problem is remedied. For example, when the MIL is illuminated for an Oxygen Sensor fault, the Task Manager does not run the Catalyst Monitor until the Oxygen Sensor fault is remedied. Since the Catalyst Monitor is based on signals from the Oxygen Sensor, running the test would produce inaccurate results.
- Conflict There are situations when the Task Manager does not run a test if another monitor is in progress. In these situations, the effects of another monitor running could result in an erroneous failure. If this conflict is present, the monitor is not run until the conflicting condition passes. Most likely the monitor will run later after the conflicting monitor has passed. For example, if the Fuel System Monitor is in progress, the Task Manager does not run the EGR Monitor. Since both tests monitor changes in air/fuel ratio and adaptive fuel compensation, the monitors will conflict with each other.
- Suspend Occasionally the Task Manager may not allow a two-trip fault to mature. The Task Manager will suspend the maturing of a fault if a condition exists that may induce an erroneous failure. This prevents illuminating the MIL for the wrong fault and allows more precise diagnosis. For example, if the PCM is storing a one-trip fault for the Oxygen Sensor and the EGR monitor, the Task Manager may still run the EGR Monitor but will suspend the results until the Oxygen Sensor Monitor either passes or fails. At that point the Task Manager can determine if the EGR system is actually failing or if an Oxygen Sensor is failing.
DIAGNOSTIC TROUBLE CODE PRIORITY
With OBD-II, different DTC faults have different priorities according to regulations. As a result, the priorities determine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher priority overwrite lower priority DTCs.
- Priority 0 This is a non-emissions related DTC.
- Priority 1 One trip failure of a two-trip DTC for non-fuel system and non-misfire conditions.
- Priority 2 One trip failure of a two-trip DTC for fuel system rich or fuel system lean condition, or misfire condition.
- Priority 3 Two trip failure for non-fuel system or non-misfire condition, or a matured one-trip comprehensive component fault.
- Priority 4 Two trip failure for matured fuel system rich or fuel system lean and misfire condition, or a one-trip catalyst damaging misfire.
Non-emission related failures have no priority. One trip failures of two-trip faults have low priority. Two trip failures or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence over non-fuel system and non-misfire failures.
DTC SELF ERASURE
With one-trip components or systems, the MIL is illuminated upon test failure and DTCs are stored. Two-trip monitors are components requiring failure in two consecutive trips for MIL illumination. Upon failure of the first test, the Task Manager enters a maturing code. If the component fails the test for a second time the code matures and a DTC is set. After three good trips, the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again. For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order to record a good trip. A Similar Conditions Window is when engine RPM is within +/-375 RPM and load is within +/-10 percent of when the fault occurred. It is important to understand that a component does not have to fail under a similar window of operation to mature. It must pass the test under a Similar Conditions Window when it failed to record a Good Trip for DTC erasure for misfire and fuel system monitors. DTCs can be erased anytime with a DRB III. Erasing the DTC with the DRBIII(R) erases all OBD-II information. The DRBIII(R) scan tool automatically displays a warning that erasing the DTC will also erase all OBD-II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.