← Back to list

97 Dodge Ram 1500 3.9L V6 - P0420 and P0320 Codes: Diagnosis and Repair Guide

Model: 97 Dodge Ram 1500 3.9l V6 Fault Code: P0320 Posted: 2006-08-27 14:28

My 1997 Dodge Ram 1500 with a 3.9L V6 engine has been failing emissions due to persistent P0320 (Ignition/Distributor Engine Speed Input Circuit Malfunction) and P0420 (Catalyst Efficiency Below Threshold) codes. Despite passing the actual exhaust test, which reported the catalytic converter as functioning properly, I'm still unsure of the root cause. I suspect that the P0320 issue may be contributing to or triggering the P0420 code. The vehicle runs smoothly with excellent drivability—so the presence of a check engine light is surprising. My next step is to reset the OBD-II system to monitor whether these codes reappear after repairs. I'm seeking advice on how to properly reset the system and what diagnostic steps to take before replacing parts such as ignition components or the catalytic converter. Any insights, especially from owners of similar 1997 Dodge Ram models with high mileage, would be greatly appreciated.

Related fault codes
P0320P0420
Comments (8)
Anonymous 2006-08-28 05:33

The truck has around 92,000 miles and has been a reliable performer—runs like a kitten, growls like a lion! Crankshaft position sensors are common failure points on this model. A scope test is the best way to verify sensor signal integrity. Poor fuel quality or incorrect fuel grade could also cause P0420 if oxygen sensors are sweeping rapidly and the converter is otherwise functional. Good luck—please update us on your progress, Jeff.

Anonymous 2006-08-28 07:59

I have about 92k miles on this truck. It's been a solid performer—smooth as silk, powerful when needed! Just a fun fact: it purrs like a kitten and growls like a lion—very loyal companion!

Anonymous 2006-08-28 09:50

I've seen many posts suggesting I reset the OBD-II system to check if codes return. However, I'm not sure how exactly to do this. Can you walk me through the steps?

Anonymous 2006-08-28 15:23

You can reset the OBD-II system using a code reader, scan tool, or by disconnecting the battery for about 10–15 minutes. This is standard procedure—just ensure you're not relying on it as a fix without proper diagnostics.

Anonymous 2006-08-28 17:13

I'm confident that simple fixes like replacing spark plugs and ignition cables won't resolve these codes, especially since P0420 typically points to catalytic converter inefficiency or sensor issues. I'm replacing the rotor, cap, and ignition wires as a first step tonight, hoping this clears the P0320 code. I'll also use premium fuel in hopes of improving combustion efficiency—crossing my fingers and tossing salt over my shoulder while spinning three times for good luck!

Anonymous 2006-08-29 05:54

None of those fixes are likely to resolve the P0320 or P0420 issues. The crankshaft position sensor is probably the real culprit—aftermarket sensors often fail to perform properly. A genuine replacement converter may cost about the same as a new crank sensor. If you're replacing spark plugs, make sure to use the correct Champion brand (or OEM equivalent) designed for this engine model. Using incorrect plugs can generate codes like P0171 but not P0420. I've had no success with aftermarket sensors—stick to factory-grade parts.

Anonymous 2006-08-30 08:09

I replaced the spark plugs (Bosch Platinum) and plug wires (Duralast), then reset the ECU by disconnecting the battery. After driving approximately 150 miles (commuting back and forth twice, plus errands for my wife), I took it in for a re-emissions test. It passed! No check engine light has come on since—driving normally again. Total repair cost: $60, including tools like a torque wrench, plug socket, extension bar, and an air freshener. I'll update if the issue returns.

Anonymous 2006-08-30 13:00

Okay! Honestly, I hate those spark plugs—especially aftermarket ones. They don’t perform well on older engines like this one.