What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles. Although generic, specific repair steps may vary by make/model.
Knock sensors are used to detect engine pre-detonation (engine knock or ping). The knock sensor (KS) is typically a two-wire sensor. A 5-volt reference is provided to the sensor and there is a signal return from the knock sensor to the PCM (Powertrain Control Module).
The sensor’s signal wire informs the PCM when a knock occurs and to what degree of severity. The PCM will retard spark timing to prevent pre-detonation. Most PCMs have the capability to learn spark knock trends in the engine during normal operation.
If the PCM determines that the knock is out of the ordinary or that the noise level is abnormally high for knock sensor #4 on bank 2, P033D may set. If the PCM detects that the knock is severe and cannot be eliminated by retarding spark timing, P033D may set. Keep in mind that knock sensors cannot distinguish between pre-detonation knock and engine mechanical problem noises. Bank 2 is always the engine side that does not contain cylinder #1. Refer to a vehicle-specific repair guide to determine the location of sensor #4 on your particular vehicle.
Symptoms
Symptoms of a P033D DTC may include:
MIL (Malfunction Indicator Lamp) illumination
Audible knocking from the engine compartment
Engine ping during acceleration
Causes
Potential causes of a P033D code include:
Damaged knock sensor connector
Knock sensor circuit open or shorted to ground
Knock sensor circuit shorted to voltage
Failed knock sensor
Moisture in knock sensor connectors
Incorrect fuel octane
Failed PCM
Possible solutions
If engine knocking is audible, first correct the source of the mechanical problem, then retest. Ensure the correct fuel octane has been used in the engine. Using fuel with a lower octane rating than specified can cause knocking or detonation and may trigger P033D.
Disconnect the knock sensor and check for water or corrosion in the connector. If the knock sensor has a seal, check that no engine block coolant is fouling the sensor. Repair as necessary.
Turn the ignition to the ON position with the engine off. Verify that 5 Volts are present at the KS connector. If so, check the proper resistance between the KS terminal and engine ground. You will need a vehicle specification for this. If the resistance is out of specifications, replace the knock sensor. If the resistance is normal, reconnect the KS and start the engine at idle. Using a scan tool in the data stream, observe the KS value. Does it indicate that knocking is present at idle? If so, replace the knock sensor. If the knock sensor shows no knocking at idle, tap on the engine block while observing the knock signal. If it does not show a signal corresponding to the taps, replace the knock sensor. If it does, check that the knock sensor wiring is not routed next to ignition wires. If there was no 5 volts present at the knock sensor connector when it was disconnected with KOEO (Key On Engine Off), go back to the PCM connector. Turn off the ignition and cut the 5-volt knock sensor reference wire in an easily repairable location (or remove the wire from the PCM connector). With KOEO, check for 5 volts from the PCM side of the cut wire. If 5 volts is not present, suspect a faulty PCM. If 5 volts are present, repair the short circuit in the 5-volt reference circuit.
Since the reference circuit is a shared circuit, you will need to check all engine sensors that receive a 5-volt reference. Disconnect each sensor one by one until the reference voltage returns. When it returns, the last sensor you disconnected is the shorted sensor. If no sensor is shorted, check that the wiring harness is not shorted on the reference circuit.