BB (187), Evap Emission System Blockage Detected

Description
Under conditions required for the evaporative emission control system monitor to run, the PCM will set DTC 187 during the EVAP Leak Detection Test if it detects a condition of no air flow through the evaporative emission control system.




DTC 187 can set under any of the following conditions:
- Blockage between the fuel tank and leak detection pump (blockage in OFLV, rollover valve, or hoses)

During the test for blockage, system pressure is maintained until the purge system is operated, in effect creating a leak. If the LDP cycle rate increases due to flow of the purge system, the test is completed. However, if a blockage in the system is detected, DTC 187 is set.

DTC 187 Diagnosis

IMPORTANT: Before beginning this procedure, repair all vehicle conditions for DTCs that are not related to the EVAP system. If more than one EVAP system DTC is set, diagnose and repair in the following order:
1. DTC 183
2. DTC 184
3. DTC 187
4. DTCs 160/161

1. Disconnect the vent valve vacuum line, and plug the end of the disconnected hose.
2. Disconnect the vent valve purge lines (2 places) and connect both of the disconnected hoses without going through the vent valve.










3. Inspect the overflow limiter valve (OFLV) as follows:
a. Remove the fuel cap.
b. Using your finger, depress the flapper valve fully to move the OFLV shutter valve and plunger.
The plunger should move out.
c. Install the fuel cap and tighten until you hear three clicks. As the fuel cap is installed, the OFLV plunger should be pushed in by the cap.
d. Remove the fuel cap. Measure the distance between the edge of the fuel filler neck and the OFLV plunger.
- If the distance is 28 mm or more, install the fuel cap. Then go to Step 4.
- If the distance is less than 28 mm (1.1 in.), replace the fuel tiller neck. Then go to the Readiness Test. 48 Readiness Test

CAUTION: The vehicle fuel tank must be at least one half full of fuel when performing the following test procedure. Pressurizing a fuel tank containing less than three gallons could result in explosion.

Follow the pump manufacturer's safety precautions. To prevent ignition of explosive gases when using the tester, keep lighted cigarettes, sparks, flames, and other ignition sources away from the test area. Keep the test area well ventilated.




4. Confirm that the EVAP pressure pump (Miller Tool No. 6872A) is operating properly. Perform the self test as described in the manufacturer's instructions.
5. Install the EVAP pressure pump to the vehicle as described in the pump manufacturer's instructions.




6. Enter LDP Hold Mode by following the scan tool selection sequence shown in the illustration at left.
7. Apply at least 51 kPa (7.40 psi) of continuous negative pressure to the vacuum line which was disconnected from the LDP intake plenum to pull up the LDP diaphragm and close the vent valve.

NOTE:
- A hand operated vacuum pump may not provide sufficient vacuum for this procedure.

- These test procedures refer to EVAP pressure pump "stall." This means that the pump does not run smoothly; it "chugs" or "burps."




8. Connect the EVAP pressure pump to the service port. Set the Pressure Hold valve to OPEN and the Vent valve to CLOSED. Turn the timer on.
a. If the EVAP pressure pump runs smoothly for longer than five seconds but stalls before one minute, go to Step 9.
b. If the EVAP pressure pump begins to stall within five seconds, there is a blockage between the fuel tank and the service port. Go to Step 10.
c. If the EVAP pressure pump runs continuously for longer than one minute without stalling, the pump may not be operating properly or the LDP may not be properly sealing the system. Repeat Steps 4 through 7.




9. At the LDP, disconnect the hose leading from the canister.
a. If the EVAP pressure pump begins to run continuously when the hose is disconnected, the condition which caused DTC 187 to set is not present at this time.
It is possible that intermittent blockage is present at the fuel filler neck plunger, the rollover valve, the liquid separator or the leveling valve. Check these areas carefully for blockage and repair blockage as required. Then go to the Readiness Test. 48 Readiness Test
b. If the EVAP pressure pump continues to stall when the hose is disconnected from the LDP disconnect the same hose at the canister.
1. If the EVAP pressure pump begins to run continuously, a blockage exists in this hose. Repair the blockage or replace the hose. Then go to the Readiness Test. 48 Readiness Test
2. If the EVAP pressure pump continues to stall, repair the blockage or replace the canister. Then go to the Readiness Test. 48 Readiness Test




10. At the canister, disconnect the hose leading to the liquid separator.
a. If the EVAP pressure pump continues to stall when the hose is disconnected, go to Step 11.
b. If the EVAP pressure pump begins to run continuously, there is a blockage between the canister and the fuel tank. Go to Step 12.




11. At the canister, disconnect the hose leading to the floor pipe.
a. If the EVAP pressure pump begins to run continuous. when the hose is disconnected, replace the canister. Then go to the Readiness Test. 48 Readiness Test
b. If the EVAP pressure pump continues to stall when the hose is disconnected, there is blockage in the purge line to the canister. Repair the blockage, then go to the Readiness Test. 48 Readiness Test




12. There is a blockage between the canister and the fuel tank in one of the following locations:
- Liquid separator
- Leveling valve
- OFLV
- Rollover valve
- Hoses and lines between the canister and fuel tank
To pinpoint the blockage location:
a. Reconnect the hose from the floor pipe to the canister. Allow the EVAP pressure pump to pressurize the system and stall again.
b. Systematically disconnect and reconnect the hose and lines between the canister and fuel tank to isolate the blockage.
Repair or replace as necessary. Then go to the Readiness Test.