2005 Grand Caravan P0499 Code: Diagnosing Vacuum Leak After Replacing Canister Purge Valve and NVLD
I own a 2005 Grand Caravan with a 3.8L engine that has thrown a P0499 fault code. I recently replaced both the canister purge valve and the Negative Voltage Leak Detector (NVLD), but the check engine light hasn't reset even after completing the drive cycle. During my latest inspection, I measured the NVLD voltage: 5V when the engine is off and 10V when the engine is running. Despite these readings appearing normal, the P0499 code persists. I'm concerned that there may still be a vacuum leak or an issue with the purge system. I need to schedule an emissions test this week and would greatly appreciate any additional troubleshooting guidance on how to properly diagnose this fault.
To troubleshoot, disconnect the orange wire monitor at the key-on-engine-off (KOEO) state. Then, remove the vacuum hoses from the purge valve in the engine compartment and apply a small vacuum using a hand-held vacuum pump to the line leading to the carbon canister. Observe if the vacuum holds and whether the voltage drops from 5V to 0V. If the voltage does not drop or the vacuum fails to hold, this indicates a leak in the hose or a faulty NVLD. Since you've already replaced the NVLD, focus on checking for leaks between the purge solenoid and the canister. If the vacuum holds and the voltage remains at 或 drops to zero, then proceed to check vehicle power supply—this should transition to 10V when the engine is running.