# Will Knock sensor replacement improve MPG?



## schloppyhead (Mar 23, 2005)

I recently brought in my 2000 Frontier V6 for service at my dealer. It was shaking and shimmying on idle and the "Service Engine Soon" light came on. I asked the service advisor to check the light and the shimmying and also check why I get lousy gas mileage. I assumed all the issues (shimmying and gas mileage) were all related but my dealer said it was 2 separate things they found when they hooked up to diagnostics. The shimmying was due to misfire so they recommended injector flush, lousy fuel mileage was due to "Knock Sensor" fault. I had them do the injector flush which fixed the shimmying very nicely. But replacing the Knock Sensor for the gas mileage problem was extremely expensive so I held up on it. My question is, "does a faulty Knock Sensor lead to poor gas mileage? and will replacing it fix the problem?" Or perhaps is this a tune up issue? You thoughts on the issue will be greatly appreciated.


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## gudel (Mar 17, 2005)

my dealer keeps pushing for the fuel line service for some $200 fee. i ended up cleaning the injector myself.
what did they quote you on that knock sensor replacement job?


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## lewisnc100 (Apr 25, 2003)

Funny that they tell you the MPG drop is due to a knock sensor when you are misfiring badly enough to cause shimmying? Wow, maybe its just me, but a bad misfire might just have a negative affect on MPG. Good call on the knock sensor, fix the misfire error and your check engine light will go off, the knock sensor will not trigger it. Then see how your MPG looks. 

Also do a search on past posts on the knock sensor, there are a bunch, here's one:

http://www.nissanforums.com/showthread.php?t=56516&highlight=knock+sensor


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## schloppyhead (Mar 23, 2005)

gudel: They quoted me a little over $500 for parts and labor. Quite pricey if you ask me. But I have read that the Knock Sensor is a PITA to replace yourself.

lewisnc100: Thanx for the tip. Incidently I read some of your threads on the knock sensor. Didn't realize it, but apparently the knock sensor gives many owners problems. Any way, I fixed the misfire, but my MPG still sucks. I think I'm going to try a tune up and change tires before I take up my dealer on that knock sensor replacement fix.


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## lewisnc100 (Apr 25, 2003)

Definitely try all the normal maintenance items first before looking at the knock sensor. Also check your brakes for a sticking caliper, could cause that drop in MPG.


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## Tonyo44 (May 9, 2005)

*1998 4cyl frontier 190k knock sensor*

I've got a 98 frontier with the 4 banger. For about the past year whenever its very humid or raining out I have a bad missing problem when coming off the line. When it does this it also gives me a check engine light. I finally took it in and it was diagnosed as a bad knock sensor. I'm taking it in and having it replaced to the tune of $300. My MPG has also not been great , around 22 on the highway. Should be around 25. Also found that in order to get it to run right I have to use premium. I'll let you know how much difference it makes in my mileage after a couple of tanks. Thanks,Tony


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## tom434 (Feb 24, 2005)

lewisnc100 said:


> Definitely try all the normal maintenance items first before looking at the knock sensor. Also check your brakes for a sticking caliper, could cause that drop in MPG.


My 87 aerostar had a sticking cailper my mileage dropped from 22 to 18 replaced both mileage went back to 23mpg :cheers:


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## hawaiibrew (Sep 14, 2005)

*Mine has the same thing*

My 2000 Frontier Club cab recently had the "Service Engine Soon" light come on. The car has been running fine..no problems at all. Only 37,000 miles.

I bought a Innova 3030 OBD2 reader to try and find the problem myself.

I got two codes

Nissan DTC 1491 Vacuum Cut Valve Bypass Valve

&

Nissan DTC 0325 Knock Sensor 1 Circuit Malfunction

The 1491 I'm not too concerned with unless it's leaking gas...which it's not.

The Knock sensor seems funny since the truck is running great.

I'm guessing that the sensor itself it not working properly and is not responding to the ECU when the ECU is trying to contact it.

Anybody replaced a knock sensor on a 2000 Nissan Frontier or similar?

Dealer is going to want $$$$$$ to replace that sucker!!

The part alone is around $120.





schloppyhead said:


> I recently brought in my 2000 Frontier V6 for service at my dealer. It was shaking and shimmying on idle and the "Service Engine Soon" light came on. I asked the service advisor to check the light and the shimmying and also check why I get lousy gas mileage. I assumed all the issues (shimmying and gas mileage) were all related but my dealer said it was 2 separate things they found when they hooked up to diagnostics. The shimmying was due to misfire so they recommended injector flush, lousy fuel mileage was due to "Knock Sensor" fault. I had them do the injector flush which fixed the shimmying very nicely. But replacing the Knock Sensor for the gas mileage problem was extremely expensive so I held up on it. My question is, "does a faulty Knock Sensor lead to poor gas mileage? and will replacing it fix the problem?" Or perhaps is this a tune up issue? You thoughts on the issue will be greatly appreciated.


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