OBD Operation Summary for Fiesta - MotorCraftService.com

Canister Purge Solenoid CPS - Flow-checkThe canister purge valve plausibility checks ensure that the canister purge valve is able to be open to purge the canister,but due to consistency of the test results, the flow check will not uniquely determine a flow fault from a large leak.Therefore the large leak diagnostic fault (P0455) will be invoked.The canister purge valve plausibility checks can be done in three ways:- When NVLD II module switch closed during large leak test- When Canister load higher than a threshold during a calibrated time- With Canister purge valve control (intrusive test).The canister purge valve control can act in via flow request or pwm request. The main difference between the two testsis the following.- With PWM control CPS check make intrusive test into the ECM functionality and the reaction expected whenthe CPS valve opens, is engine parameter deviations.- With FLOW control, CPS check we make non intrusive test into the ECM functionality and the reaction expectedwhen the CPS valve opens is no engine parameter deviations.The canister purge valve control test can be done several times before an error is reported.Flow check algorithmCONTINENTAL REVISED: SEPTEMBER 17, 2010 PAGE 22 OF 111