A knock sensor signal that reads stronger than it should points to a short or a noise problem. A P0333 code means the knock sensor 2 signal reads higher than its allowed range.
This guide explains what makes the signal too strong, how to test for shorts and which repairs fix it.
P0333 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 3 | Ignition system or misfire | The fault involves the ignition system, misfire detection or engine position sensors. |
| 33 | Specific fault | Knock Sensor 2 Circuit High Input (Bank 2) |
What the P0333 Code Means
The SAE J2012 standard defines the P0333 code as Knock Sensor 2 Circuit High Input (Bank 2). Knock sensor 2 is the sensor for bank 2 on V6, V8 and some other engines with two knock sensors. Bank 2 is the side without cylinder 1. On some inline engines, sensor 2 is simply a second sensor further along the block.
A knock sensor is a small piezoelectric device bolted to the engine block, cylinder head or intake. When detonation makes the block ring at a certain frequency, the sensor produces a small AC voltage that the powertrain control module (PCM) reads.
When the PCM hears knock, it retards ignition timing on the affected cylinders until the knock stops. Many PCMs also send a small bias voltage through the sensor circuit and watch it to check that the sensor is connected and working. On many V engines, the sensors sit under the intake manifold, in the valley between the cylinder heads.
High input means the knock sensor 2 signal is stronger than expected or the circuit voltage reads high. That usually points to a short to voltage, a damaged shield picking up noise, real mechanical noise or a sensor that has failed.
Symptoms of a Bad Knock Sensor 2
With the sensor out of action, the PCM usually plays it safe. Common signs of a P0333 code include:
- Check engine light on
- Sluggish acceleration from retarded timing
- Lower fuel economy
- Pinging or knocking under load if timing is not retarded
- Engine running hotter under load
Many engines feel only slightly flat with this code, so it is easy to ignore. The extra timing retard costs power and fuel, and on some engines the protection against real knock is reduced.
What Causes the P0333 Code?
These are the usual causes:
- Signal wire shorted to voltage. Damaged insulation touches another circuit.
- Damaged shielding or ground. The wire picks up electrical noise from ignition parts.
- Real engine noise. Loose parts, a bad lifter or piston slap can create a strong signal.
- Over-tightened sensor. Too much torque can make the sensor too sensitive.
- Failed knock sensor. An internal fault changes the output.
- PCM fault. Rare.
Tools You Will Need
You can do most of this testing at home with basic tools:
- OBD-II scan tool that shows knock retard
- Digital multimeter
- Mechanic’s stethoscope
- Torque wrench
- Intake gaskets if the sensors are under the intake
How to Diagnose the P0333 Code
Check where knock sensor 2 is mounted before you start. If it is under the intake manifold, test the wiring at the PCM end first so you only remove the intake if you need to.
Check Live Data
With the engine warm, look at knock retard or knock activity for each bank in live data. A steady large retard with no audible knock, or no knock activity at all when you tap the block lightly near the sensor, points to a sensor or circuit problem.
Check for Shorts and Shield Problems
With the battery disconnected and the PCM unplugged, check the signal wire for shorts to other circuits. If the wiring has a shield, make sure it is grounded at one end only, as the service manual shows.
Listen for Real Noise
With the engine running, use a mechanic’s stethoscope near the sensor. A loud tick, knock or rattle can be real mechanical noise, which needs a mechanical repair, not a new sensor.
Check Fuel and Timing
Make sure the engine is running on the octane fuel the manufacturer requires. Low octane fuel can cause real knock, and the PCM may log a range or performance fault if it cannot control it.
How to Fix the P0333 Code
Match the repair to what your tests found. Then clear the code and drive under the same conditions that set it.
- Repair the wiring or pigtail, which many manufacturers sell separately for engines with sensors under the intake.
- Replace knock sensor 2 if it fails tests, and torque it to the exact specification.
- Fix coolant or oil leaks that damaged the wiring.
- Repair mechanical noise such as loose heat shields or noisy valve train parts.
If the sensors are under the intake, many technicians replace both knock sensors and the pigtail at the same time, since the labor to reach them is the biggest cost. Use new intake gaskets when you reinstall the manifold.
Common Mistakes to Avoid
These mistakes waste money or leave the real fault in place:
- Ignoring mechanical noises that the sensor is picking up correctly
- Routing new wiring next to spark plug wires or coils
- Using thread sealer on a knock sensor that should be installed dry
- Skipping new intake gaskets after removing the intake
Repair Cost Breakdown
The cost to fix a P0333 code depends on the cause. This table shows typical ranges for parts and labor.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Knock sensor | $20 to $100 | $150 to $350 |
| Knock sensor pigtail | $20 to $60 | $150 to $300 |
| Sensors under the intake, labor included | $60 to $200 | $400 to $900 |
| Intake gasket set | $20 to $80 | Usually included |
Where the sensor sits makes the biggest difference. A block-mounted sensor on the side of a four-cylinder engine may take half an hour, while sensors in the valley of a V8 can take several hours.
Is It Safe to Drive with a P0333 Code?
Usually, yes. The PCM retards timing to protect the engine, so it runs a little slower and uses a little more fuel.
Use the octane fuel your owner’s manual lists, and avoid heavy loads and towing until it is fixed. If you hear pinging or knocking under load, ease off, since real detonation can damage pistons.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0330 | Knock Sensor 2 Circuit Malfunction (Bank 2) |
| P0331 | Knock Sensor 2 Circuit Range/Performance (Bank 2) |
| P0332 | Knock Sensor 2 Circuit Low Input (Bank 2) |
| P0334 | Knock Sensor 2 Circuit Intermittent (Bank 2) |
| P0325 | Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor) |
Getting Knock Sensor 2 Working Again
A P0333 code means the knock sensor 2 signal is too strong. Shorts, damaged shielding and real mechanical noise cause most cases.
- Check knock retard in live data.
- Inspect the wiring and connector.
- Measure the sensor and check its torque.
- Listen for mechanical noise.
- Use the correct octane fuel.
Frequently Asked Questions
Can Spark Plug Wires Cause the P0333 Code?
They can. Knock sensor wiring carries a very small signal, so it picks up electrical noise easily. Routing it near coils or plug wires, or a damaged shield, can make the signal read too high.
Where Is the Knock Sensor?
On many four-cylinder engines, it bolts to the side of the block under the intake manifold. On many V6 and V8 engines, such as GM’s 5.3L and several Toyota and Lexus engines, the sensors sit in the valley under the intake manifold.
Do Knock Sensors Need a Special Torque?
Yes. A knock sensor works by picking up vibration, so it must be tightened to the correct torque on a clean surface. Too loose and it misses knock, too tight and it may become too sensitive. Check your service manual.
Should I Replace Both Knock Sensors?
If both sit under the intake, many technicians replace both at once. The labor to reach them is the biggest cost, and the second sensor is usually just as old. On engines where the sensors are easy to reach, replace only the one that tests bad.