A little more than a week ago, my check engine light came on. Just today, I took my car to Auto Zone so they could hook a computer up and check the codes. They told me that the knock sensors were bad and that I should have them replaced as soon as possible. The problem is that they are $100 a piece. I want to attempt to replace them myself, but I don't know where they are located. If you could let me know where they are located that would be great!

I have a 1999 Volvo S70 non-turbo. I just recently bought it and it has 186,000 miles.

Thanks!

 

Assuming they're the same as 850 (should be) they're on the front of the engine block; have to pull intake manifold to even see them.

Do a search on this site for "knock sensor"; should find plenty of info...

BTW: They rarely fail; more likely the last person who worked on it forgot to hook them up...

 

Thanks, I'll have a look at that then. But you make an interesting remark; "they rarely fail". I've heard the engine described as sounding like marbles, but my engine runs perfectly. No noises or anything. But the check engine light is still on for that "problem". Could it possibly just be an error in the computer and not actually an issue with the knock sensors. Maybe I could just reset the light?

 

Yes, always reset the CEL to make sure the code comes back (at least once..) before you start replacing parts...

 

One thing that professional auto mechanics understand, that many parts store people and DIYers don't is that trouble codes DO NOT tell you what's wrong with your car. They are guidance, they can help you find the trouble, but never just throw parts at the problem without testing and examining things first. Check the wiring to the sensors, check your ignition system, check the mounting bolt on the sensor- if that's loose, it will rattle around randomly, thus sending an errant signal to the ECU. If basic visual checks don't find the trouble, get a good service manual, or (even better, I think) get a subscription to Alldata's DIY service- it's 20 bucks/ year per car, and you'll get access to Volvo's own diagnostic charts and wiring diagrams.

Trouble codes, I always tell people, are the car telling you where it hurts. If you go to the doctor, and say your knee hurts, does he say you need a new knee? Of course not! he checks you out and finds the source of the problem, before recommending treatment. Your car is telling you that something hurts- doesn't mean it's broken- you just have to check it out.

And no, these cars aren't supposed to sound like a can of marbles. They often do, when something is wrong.

 

Ditto, and well said, if I may say so..

akem21; let us know what you find...

 

Thanks for all the help! A guy I know checked the codes with his computer and we didn't find any codes for the knock sensors... I probably won't trust AutoZone again. But we reattached a vacuum line on the air intake and reset the Check Engine Light and it hasn't come back on yet, so that's a good sign. We did see one code though... I believe it was P1080. The computer didn't recognize what the code was for. Have any ideas?

Thankfully I didn't have to pull anything apart yet!

 

Oh, I'll bet the codes for the knock sensors were actually there.. you just got a great look at what I was talking about. The knock sensors were telling the computer exactly what they were seeing- they were working fine. However, based on the info it was getting from all other sensors, the knock sensor was sending the computer different information that it expected to get. Why? Well, that vacuum line, being disconnected, was allowing air into the engine that the computer didn't know about, as it didn't enter through the MAF. This probably caused a couple cylinders to run lean. Lean running can cause knock, which the knock sensors detected, but the computer didn't expect, because it was probably more severe at idle/ low load conditions, when spark knock usually occurs under heavy load. So, the computer said "hey! those knock sensors are sending unexpected information! And it flags them with a code. Here's where actual diagnosis, as opposed to mere parts replacement, comes in to play- it's your job to find the actual cause. And it's possible that the knock sensor codes were there when AZ checked, and not when you did later, because they were probably intermittent codes. As for code 1080, any codes that don't have a "0" after the letter are manufacturer specific, so universal scanners won't have a definition, as the definition varies between manufacturers. The guy at AZ probably saw that that code had no definition and simply ignored it, when it could have been the more important code. On the other hand... not even alldata has a definition for THAT code. Strange. Anyhow, hopefully the problem doesn't come back.