Hi guys i have a 1999 Nissan Altima, its a 4 Cylinder 2.4 engine i need to pass inspection and im having major problems with check engine light , there are two codes that keep showing up P0325 Knock Sensor 1 Circuit Malfunction Bank 1 or 1 sensor, and P0720 Output Speed Sensor Circuit Malfunction, these are the codes that show up. Now i have changed the Speed Sensor on the car and after reset and driving for around 70 miles the check engine comes back on and also it still shows that same code for Speed Sensor which i have already changed ? Can some one give me a diagram where the Knock Sensor is located in the car ? And why would the Speed sensor code show up when i changed it with a new one ? Any help will be greatly apreciated.

P0720:

Possible causes
- Speed sensor harness or connectors
- Sensor circuit is open or shorted
- Speed sensor

When is the code detected?
Diagnostic trouble code is detected when Transmission Control Module (TCM) does not receive the proper voltage signal from the sensor.

Might not be the sensor itself if the sensor was replaced. Could be the wiring/harness to TCM.


P0325:


Possible causes
- Knock sensor circuit short to ground.
- Knock sensor circuit short to power.
- Knock sensor circuit open.
- Damaged knock sensor.
- Powertrain Control Module (PCM) or Electronic Control Module (ECM)

Possible solution
- Repair or resecure harness or connector
- Replace knock sensor Bank 1 (Bank 1 if applicable)
- Replace PCM/ECM


Factory Service Manual for your car: http://www.nicoclub.com/FSM/Altima/1999/

ec.pdf page 241 - Knock Sensor.

Although, the sensor may be fine... maybe your motor is knocking slightly and you don't realize it. Put in 91 Octane. See if that code stays off after it's cleared.

Get it fixed?