What Does P033C Mean?
The knock sensor 4 on bank 2 is reporting an abnormally low voltage signal to the ECM. The signal is below the minimum threshold expected for normal operation, meaning the ECM cannot effectively detect engine knock on the affected cylinders. The driver may notice reduced power and degraded fuel economy as the ECM defaults to safe ignition timing maps.
Common Causes
35%
Failed knock sensor 4 with weak or dead piezoelectric element producing insufficient voltage
25%
Open circuit in the knock sensor 4 signal wire preventing the signal from reaching the ECM
20%
Corroded connector pins creating high resistance and attenuating the knock sensor signal to below threshold
10%
Short to ground on the knock sensor 4 signal wire pulling the voltage below normal operating range
10%
Poor ground connection in the knock sensor 4 circuit
Diagnostic Steps
1
Monitor knock sensor 4 voltage on live data and compare to the other knock sensors — a consistently lower reading than sister sensors confirms the low signal condition.
2
Disconnect the knock sensor 4 connector and measure the sensor resistance — it should read approximately 500–600 kOhms; an open reading (OL/infinite) confirms sensor failure.
3
Check for continuity in the signal wire from the knock sensor 4 connector to the ECM connector pin — an open circuit will prevent any signal from reaching the ECM.
4
Inspect the connector terminals for corrosion, green oxidation, or signs of moisture intrusion — clean with electrical contact cleaner and verify positive pin engagement.
5
With the sensor disconnected, measure from the signal wire to chassis ground to check for a short to ground — should read infinite (OL); any low resistance value indicates insulation damage.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The knock sensor 4 on bank 2 is reporting an abnormally low voltage signal to the ECM. The signal is below the minimum threshold expected for normal operation, meaning the ECM cannot effectively detect engine knock on the affected cylinders. The driver may notice reduced power and degraded fuel econ...
The most common cause of P033C (Knock Sensor 4 Circuit Low (Bank 2)) is: Failed knock sensor 4 with weak or dead piezoelectric element producing insufficient voltage
Typical repair costs for P033C range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive under normal conditions. The ECM protects the engine by retarding timing, which reduces performance but prevents damage. The risk is that genuine engine knock cannot be detected on the affected cylinders, so avoid high-performance driving, towing, and use the recommended or higher-octane fuel.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P033C to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition System
Difficulty
Type
Generic (SAE)
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