1998 Dodge Grand Caravan P0420 Code: Causes, Fixes, and Emission Test Tips

When did you first take your vehicle to AutoZone to check the code—before or after visiting the Dodge dealership? If after, was the original code when the light came on two years ago known? Do you have the repair invoice from the previous service visit? That document should detail the diagnosed issue and work completed. This would help determine whether the current P0420 problem is a repeat of the earlier fix. Is it possible that the same underlying issue is recurring, or could different problems be causing the code to appear intermittently? If the same P0420 code returns after two to three months, this strongly suggests an intermittent fault. Such issues can be difficult to diagnose and may require specialized equipment. If the code varies each time, that would indicate multiple problems—though I suspect it's likely a single root cause. Gary

Thanks Gary. I visited AutoZone four to five times—both before and after taking the car to the dealership. Each time, the code displayed was P0420. The dealer performed a comprehensive tune-up: replaced spark plugs, fixed an engine gasket leak, repaired coolant leaks, etc.—but no work was done on the oxygen sensors or related emissions components.

Check out these helpful resources. One post in the first thread references a technical article by a technician about catalytic converter efficiency failures—this is directly relevant to P0420. Resource 1: http://www.batauto.com/Forums/index.php?topic=31680.msg31680#msg31680 Resource 2: http://www.troublecodes.net/articles/catfailure/ The seventh post in that thread includes a diagnostic flowchart that can guide you through identifying the root cause. Even if you don't fully understand it, having this knowledge will allow you to communicate more effectively with service technicians or dealership managers. You can ask upfront whether they charge for follow-up repairs on the same issue—many dealerships do not have clear policies here. Also, inquire about their testing equipment: advanced diagnostics are essential to avoid simply replacing parts without addressing real faults—a common problem in many shops. My recommendation is that you seek a reputable dealership or an advanced independent repair shop with proper diagnostic tools. These facilities may cost more initially due to high investment in equipment—but if they offer a warranty (e.g., 3, 6, or 12 months), it’s worth the price. This helps prevent repeated charges and builds trust. Be sure to explain that you drive long distances before the MIL reactivates—this is normal for P0420-related issues—and agree on a clear warranty period (e.g., 3 months) in advance. Unmet expectations are often the root cause of dissatisfaction, regardless of whether it's a personal or business relationship. Gary

Thanks Gary! I’ve read those articles—they’re very informative and technically detailed, but still beyond my understanding. It seems like the check engine light might be stubborn—but I’m now realizing it could also be expensive to fix if it's not properly diagnosed. I’ve been disconnecting the battery each time until I eventually sell the car. Currently, I drive with the light on unless I need to pass an emission test, when I temporarily disable it by removing the battery.

Not stubborn—likely expensive and possibly unrelated! The P0420 code is often a symptom of deeper emissions system issues, not just a simple intermittent fault. It's important to diagnose properly using advanced tools before replacing parts. A misdiagnosis could lead to unnecessary repairs or poor long-term performance.