# Knock Sensor? Help!!



## Frontier00 (Aug 22, 2007)

My engine light has been on for several weeks, so I took my truck to my mechanic and he ran the diagnostics, afterwards he told me that the front two sensors where bad and also it showed a code for the knock sensor. He replaced the front 02 sensors and cleared the codes, he also told me the knock sensor code is a ghost code that is triggered anytime an oxygen sensor code goes off. However, my light is back on. So I called him and he told me that sometimes the dealers need to flash the computer. So I took it to the dealer today, and they ran the diagnostics of course and told me that the two oxygen sensors and the knock sensor are triggering. Why would the oxygen sensors still trigger if they have been replaced and is the knock sensor a ghost code or does it really need to be replaced? Help Please!! Sorry I forgot to say that I have a 2000 frontier 2wd SE crew cab.


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## azrocketman (Oct 5, 2005)

Frontier00 said:


> My engine light has been on for several weeks, so I took my truck to my mechanic and he ran the diagnostics, afterwards he told me that the front two sensors where bad and also it showed a code for the knock sensor. He replaced the front 02 sensors and cleared the codes, he also told me the knock sensor code is a ghost code that is triggered anytime an oxygen sensor code goes off. However, my light is back on. So I called him and he told me that sometimes the dealers need to flash the computer. So I took it to the dealer today, and they ran the diagnostics of course and told me that the two oxygen sensors and the knock sensor are triggering. Why would the oxygen sensors still trigger if they have been replaced and is the knock sensor a ghost code or does it really need to be replaced? Help Please!! Sorry I forgot to say that I have a 2000 frontier 2wd SE crew cab.


What are the actual codes? The OBDII will provide codes that are symptoms of a problem but not the actual problem.

For example, my Windstar will flash a code that one of its oxygen sensors is not switching and is indicating out of range lean. The problem, based on Ford technical bulletins, is not the oxygen sensor but the mass air flow (MAF) sensor. If the MAF gets dirty the OBD II will lean out the engine operation until it hits its limits (and then the check engine lamp lights up). Generally, there is nothing wrong with the oxygen sensor.

Do a web search on your actual codes. There may be advice in a service bulletin that your dealer is too lazy to research (I know my Nissan dealer was too lazy to search their bulletins when my Frontier flashed some EGR codes). Also, the dealer test set (CONSULT II) may be able to search trim values and other data in what is called a parameter identification display (PID, at least that's what Ford calls it). This may indicate what the engine is trying to do and point to the real culprit.

As a long shot, clean your MAF sensor. Spray some TV tuner cleaner (without lubricant) on the sensor. If you want, use a cotton swap VERY gently on the sensor as it is delicate. There is a possiblity that the Frontier behaves like the Windstar and leans the engine out because of a dirty sensor. A lean mixture may trigger oxygen sensor failure indications (as it does in the Windstar) and will also cause engine detonation (causing a knock sensor failure).

Some other information like vehicle mileage may also help others suggest a problem cause.

Steve


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## azrocketman (Oct 5, 2005)

You might also want to look at this:Service Bulletins Nissan Cars

Steve


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## smj999smj (Jan 1, 2006)

Yeah, a lot of O2 sensor codes were set because of the ground issue as the link to the TSB shows. The ground kit is very expensive from Nissan, but can be easily made with some eyelet connectors, 10 gauge wire, some electical tape or conduit to insulated the harness and two 8X1.25MM bolts. You may have not needed the sensors, at all. 

FYI, there is no such thing as a "ghost code," and a knock sensor code does not automatically set because an O2 sensor set a code. Assuming there is no open or short in the knock sensor circuit, the kncok sensor will set a code when it detects engine "knock." That could be "knock" as in preignition detonation, or "knock" as in a mechanical knock, such as a bad rod bearing. The grounds in concern are for the EGI harness, so there are a number of engine management items that are grounded at that point. One of them MAY be the knock sensor (I would have to check a wiring diagram to be sure.). If one or more engine management items are not working properly, ie a front O2 sensor(s), then the engine might run lean and cause detonation, triggering the knock sensor code.


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## azrocketman (Oct 5, 2005)

smj999smj said:


> Yeah, a lot of O2 sensor codes were set because of the ground issue as the link to the TSB shows. The ground kit is very expensive from Nissan, but can be easily made with some eyelet connectors, 10 gauge wire, some electical tape or conduit to insulated the harness and two 8X1.25MM bolts. You may have not needed the sensors, at all.



10 AWG (American Wire Gauge) wire is pretty heavy for a return line that is carrying relatively low current. I would say that 16 AWG is more than adequate and you can get away with 18 AWG wire.

Steve


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## Frontier00 (Aug 22, 2007)

Sorry that it has taken me so long to respond to your answers. I have had problems logging in to the site. I forgot to put down my mileage 100,500. and the trouble codes were p0131, p0151, p0325. I am definitely going to try the ground issue. I showed the service bulletin to my mechanic and he is going to try that out. Do you think that it could be a bad ECU? Also since my o2 sensors have been replaced would my car pass an emissions test or will it fail since the codes are still showing up? I appreciate the help.


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## azrocketman (Oct 5, 2005)

Frontier00 said:


> Sorry that it has taken me so long to respond to your answers. I have had problems logging in to the site. I forgot to put down my mileage 100,500. and the trouble codes were p0131, p0151, p0325. I am definitely going to try the ground issue. I showed the service bulletin to my mechanic and he is going to try that out. Do you think that it could be a bad ECU? Also since my o2 sensors have been replaced would my car pass an emissions test or will it fail since the codes are still showing up? I appreciate the help.


P0131 - Front O2 Sensor, Bank 1 Lean Shift Monitoring
P0151 - Front O2 Sensor, Bank 2 Lean Shift Monitoring
P0325 - Knock Sensor, Bank 1

Clean your Mass Air Flow (MAF) sensor. Use electronic contact cleaner (no lubricant) to spray on the sensor. You can use a cotton swab to rub the sensor if you are very careful. The sensors use delicate wires to measure the airflow. My experience with cleaning sensors is hit and miss. Most of the auto makers will specify new sensors but cleaning is worth a try. If you are not sure have your mechanic do it.

I do not think you have an ECU problem. Your symptoms are consistent with a dirty MAF sensor.

Your vehicle, at least in Arizona, will not pass an emissions test. A lit check engine light will automatically fail you. In Arizona they connect to the OBD II connector to check its status. You failure codes will be read and they will also flunk you. Forget trying to erase the codes and resetting the light just before you go through emisssions. The OBDII system will indicate "not ready" when checked. THe OBD II requires about a 20 minute drive cycle to complete all of its tests before it is "ready" for emissions testing.

Steve


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