Truck Trend Garage: 2000 Nissan Frontier P0300 and P0400 Codes
Question: I've already done a lot of work to a 2000 3.3-liter Nissan Frontier Crew Cab. It runs bad and has two codes, P0300 and P0400. I spoke to a mechanic who thought I should change the passenger-side catalytic converter. I want to be sure before I spend any more money.
| Truck Trend Garage Misfire
Answer: Good call on double-checking. Don't know where your mechanic friend got his information, but P0300 and P0400 have nothing to do with a catalytic converter. P0300 is caused by a random cylinder misfire. But these earlier systems that were capable of determining a misfire, often set a random misfire code and/or codes for misfires at all six cylinders -- while the problem was a dead miss at one particular cylinder. Newer systems are more capable of narrowing down exactly which cylinder is causing the problem. P0400 indicates a problem with the EGR (Exhaust Gas Recirculation) system. The system blends exhaust gas with the air/fuel mixture entering the engine to reduce combustion temperature and emissions output. A red flag is the potential for an EGR problem (EGR valve stuck open), to cause multiple misfires, due to too much exhaust mixed with the air/fuel mixture. First attempt a cylinder balance test. You may have two unrelated problems and a single dead cylinder. If you can't narrow down the miss to one cylinder, that can be another hint as to whether the EGR valve is causing the problem. As usual, with this kind of stuff, it takes experience and real-world testing to produce an accurate diagnosis.
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at trucktrend@sourceinterlink.com. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.
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