Persistent P0325 and P0330 Codes in a 2001 Toyota Sienna: Causes and Diagnosis

When your check engine light pops on and you pull codes P0325 and P0330 on a 2001 Toyota Sienna, it’s basically the van’s way of saying, “Hey–something’s not right in the knock sensor system.” And if you’ve already replaced the knock sensor and the harness, only to have the codes come right back after an ECU reset… yeah, that’s the kind of thing that makes you want to throw a wrench across the garage.

The good news is: those repeat codes usually mean the problem isn’t as mysterious as it feels. It just means the issue is likely somewhere else in the system, not necessarily the parts you swapped.

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What the Knock Sensor Is Actually Doing

Knock sensors are like the engine’s “ears.” They listen for knock/ping, which is abnormal combustion that can happen when timing, fuel quality, carbon buildup, or engine load pushes things in the wrong direction.

On the Sienna, the knock sensor is a piezoelectric sensor mounted to the engine block. When it detects certain vibration patterns, it generates a small voltage signal and sends it to the ECU. The ECU uses that signal to adjust ignition timing (and sometimes fueling) to protect the engine.

So when the ECU sees a signal that doesn’t make sense–or no signal at all–it flags a circuit issue and stores codes:

• P0325 = Knock Sensor circuit malfunction (Bank 1)
• P0330 = Knock Sensor circuit malfunction (Bank 2)

In plain terms: the ECU isn’t happy with what it’s seeing from one or both knock sensor circuits.

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Why These Codes Can Keep Coming Back (Even After Replacing Parts)

This is where real-world troubleshooting matters, because “new part” doesn’t automatically equal “fixed.”

1) Wiring or connector problems (still the #1 culprit)

Even with a new harness, you can still have:

• corrosion or spread pins in connectors
• a wire rubbed through somewhere along the routing
• a poor ground reference
• a hidden break inside insulation
• oil/coolant intrusion into connectors

It only takes one weak connection to make the ECU think the circuit is faulty.

2) ECU issues (less common, but possible)

If the ECU can’t interpret the knock sensor signal correctly–or the input circuit is failing internally–it may keep tossing the same codes no matter what you replace. It’s not the first thing to blame, but it’s on the list once wiring checks out.

3) Installation details that actually matter

Knock sensors are picky. If the sensor isn’t mounted correctly, it may not “hear” properly. Things that can cause trouble:

• incorrect torque
• sensor not seated cleanly
• wrong sensor type/quality (aftermarket sensors can be hit-or-miss)

4) Mechanical knock vs. “circuit” codes confusion

These codes are labeled as circuit faults, not “knock detected,” but severe vibration, engine issues, or abnormal noise can sometimes muddy the waters–especially if something else is causing harsh vibrations or the wiring is intermittently failing under load.

5) Conditions that bring the problem out

Sometimes everything looks fine in the driveway, but the fault shows up when:

• the engine is hot
• you’re accelerating under load
• the harness shifts slightly
• fuel quality changes

That’s why the codes can disappear after an ECU reset… and then return once the system runs its checks again.

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How a Good Tech Typically Diagnoses It

Pros usually don’t start by throwing more parts at it–they start by proving what’s failing.

A solid diagnostic flow often looks like this:

1. Inspect connectors and routing (look for corrosion, oil, broken locks, pin fitment issues)
2. Continuity and resistance testing with a multimeter from sensor to ECU
3. Wiggle testing the harness while watching readings (to catch intermittent opens/shorts)
4. Confirm sensor type and torque spec
5. If everything checks out, then–and only then–consider ECU testing/reflash/replacement
6. If needed, investigate engine mechanical conditions that could be contributing

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Common Missteps People Make

• Assuming the sensor is the whole fix. The system includes wiring, connectors, and the ECU input circuit–any of those can trip the code.
• Blaming fuel alone. Bad fuel can cause knock, sure, but P0325/P0330 are usually about the ECU seeing a circuit problem, not simply hearing knock.
• Ignoring connector condition. A harness can be new and still connect to an old, contaminated, or damaged plug interface.

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Tools and Parts That Typically Come Into Play

To get to the bottom of it, you’re usually looking at:

• an OBD-II scan tool (to read/reset and check readiness/return conditions)
• a multimeter (for resistance, continuity, and short-to-ground testing)
• wiring repair supplies (terminals, heat shrink, dielectric grease where appropriate)
• OEM-quality knock sensors/harness (cheap parts can create repeat headaches)
• in rare cases: an ECU

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The Bottom Line

If P0325 and P0330 keep returning on your 2001 Toyota Sienna after replacing the sensor and harness, it usually means the van is pointing you past the obvious. Most of the time, the real issue is wiring integrity, connector problems, installation/torque details, or (less often) the ECU itself.

The fix isn’t guesswork–it’s a careful, step-by-step confirmation of the entire circuit from the sensors all the way back to the ECU. Once you find the weak link, the codes stop coming back for good.