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P0100, P0325, and P0304 Fault Codes on 1997 Nissan Altima: Causes and Fixes

Model: 97' Nissan Altima Fault Code: P0100 Posted: 2007-07-24 21:53

I own a 1997 Nissan Altima with nearly 200,000 miles. The vehicle has historically been reliable but now exhibits sputtering, hesitation, and occasional stalling at low RPMs. The onboard diagnostic system shows three fault codes: P0100 (Mass Airflow Sensor Range/Performance Problem), P0325 (Knock Sensor Circuit Malfunction), and P0304 (Cylinder 4 Misfire). The question is whether the engine misfire is causing the knock sensor to malfunction, or if replacing just the knock sensor would resolve the issue. Given the age of the vehicle and high mileage, I'm concerned about underlying mechanical problems such as worn ignition components, valve sealing issues, or fuel delivery faults. I've already replaced the spark plugs and checked injector resistance and balance — all readings are within normal ranges. The ignition coil wiring and distributor cap show no signs of wear or damage. However, I haven't located the knock sensor physically, which makes diagnosing it difficult. My next steps include checking compression in cylinder 4 and inspecting for intake gasket leaks around that cylinder. A common issue on older Nissan Altimas is an intake leak at the #4 runner, which can cause misfires and affect engine performance. I'm also considering fuel pressure testing and evaluating MAF sensor function as potential root causes. Any insights or recommendations would be greatly appreciated.

Related fault codes
P0100P0325
Comments (6)
Anonymous 2007-07-25 07:35

Has the vehicle had a recent tune-up? Misfires can trigger knock sensor DTCs. Some 1997 Nissan Altimas are known to have ignition coil issues — especially in older models with high mileage. A basic tune-up may resolve or at least reduce the symptoms.

Anonymous 2007-07-25 23:16

No tune-up has been performed — only regular maintenance like oil changes and tire rotation. I spent most of the day under the hood troubleshooting. Injectors were checked: they have normal resistance, produce a ticking sound, and passed balance tests. Wires and distributor cap show no wear or damage. Spark plugs were replaced during this process (costing $2 each), but the issue persists. I haven’t located the knock sensor physically — it’s likely hidden behind the intake manifold. However, I suspect that the misfire is not caused by a faulty knock sensor, but rather by an underlying mechanical problem such as poor cylinder sealing or fuel delivery issues. Next steps: inspect ignition coil performance, check compression in cylinder 4, and evaluate MAF and fuel pressure. Any suggestions are welcome.

Anonymous 2008-08-07 21:56

I'm posting to ask for advice — I have the same 1997 Nissan Altima with 180,000 miles and it's well-maintained. The check engine light came on recently, showing P0100 and P0325 codes. I don’t experience stalling at low RPMs like some others, but I do notice hesitation during idle. Should I simply replace the knock sensor to fix this? Or are there deeper issues I should investigate first?

Anonymous 2008-08-08 00:06

A faulty knock sensor is a likely cause — definitely consider replacing it. However, the misfire could stem from mechanical wear, especially at high mileage. Check cylinder compression and ensure valve sealing in cylinder #4 is intact. A worn intake gasket or leaking runner can mimic these symptoms.

Anonymous 2008-08-08 17:11

Where exactly is the knock sensor located? I’ve searched under the intake manifold but haven’t found it — could it be behind a cover or accessible only during disassembly?

Anonymous 2008-08-08 19:29

The intake gasket on cylinder #4 is likely leaking. This is a common issue in older Nissan Altimas. While you're removing the intake, consider replacing both the knock sensor and its harness. To verify, apply carburetor cleaner around the #4 runner while the engine is running — if idle behavior changes, it confirms a leak. The leak often occurs at the bottom of the intake manifold and should be thoroughly soaked.