Blocked Purge Line Diagnostics
If an in-line Fuel Tank Pressure Transducer is used, it is possible for a blockage to occur between the Fuel Tank Pressure Transducer (FTPT) and fuel tank. If this occurs, the evap monitor would run and pass all leak check diagnostics even if there is a leak at the fuel cap. (The blockage will make the system look sealed despite the leak.). The blocked line diagnostic looks for a rapid drop in pressure during Phase 0 of the cruise test. This rapid pressure drop occurs because the Canister Purge Valve (CPV) applies a vacuum to just the canister and evap lines. Upon seeing an excessively fast pressure drop in Phase 0, the evap monitor will invoke a special execution of Phase 3 & 4 where a CPV pressure pulse is applied to the evap system. This pressure pulse is at a very low flow and short duration (0.5 -1.0 seconds) to avoid drivability issues. If this intrusive test fails, the Phase 0 test and the intrusive test are repeated 2 or 3 times prior to setting a P144A DTC.
Diagram of an evaporative system with a blockage is shown below:
 Courtesy of
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EVAP BLOCKED LINE MONITOR OPERATION:
| DTC |
P144A |
| Monitor execution |
once per drive cycle |
| Monitor Sequence |
Runs during Phase 0 of evap 0.040" cruise test. Performs an intrusive test in Phase 3 & 4 to confirm a fault. |
| Sensor/Components OK |
MAF, IAT, VSS, ECT, CKP, TP, FTP, CPV, CVS |
| Monitoring Duration |
30 seconds (see disablement conditions below) |
TYPICAL BLOCKED LINE MONITOR ENTRY CONDITIONS:
| Entry condition |
Minimum |
Maximum |
| General 0.040" Cruise Test conditions apply |
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| Air mass high enough for intrusive portion of test |
1.5 (lb/min) |
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| Manifold vacuum high enough for intrusive portion of test |
5 "Hg |
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| Not in open loop fueling |
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| CPV purging |
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TYPICAL EVAP BLOCKED LINE ABORT CONDITIONS:
| All items cited under entry conditions apply. |
TYPICAL EVAP BLOCKED LINE MALFUNCTION THRESHOLDS:
P144A: Phase 0 portion of test delta pressure < -5 "H2
0/sec
P144A: Phase 3 & 4 (intrusive test) pressure response < -2 "H2
0 |
J1979 EVAPORATIVE SYSTEM MODE $06 DATA
| Test ID |
Comp ID |
Description |
Units |
| $3D |
$80 |
Blocked Evap System Line - Screening test (P144A) |
Pa/sec |
| $3D |
$81 |
Blocked Evap System Line - Fault confirmation test (P144A) |
Pa |
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NOTE:
Default values (0.0) will be displayed for all the above TIDs if the evap monitor has never completed. Each TID is associated with a particular DTC. The TID for the appropriate DTC will be updated based on the current or last driving cycle, default values will be displayed for any phases that have not completed.
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