My check engine light came on about 2 months ago. I had the code pulled and it indicated a faulty knock sensor.
The car runs fine, so I was wondering if this is something that must be repaired or risk engine damage.
Second, will the car pass state emission test inspection. Third, is this repair expensive?

Appreciate feedback!

I didn't think a bad knock sensor would set off a CEL. Might be worth checking your factory service manual at www.nicoclub.com/FSM/ to make sure that's your issue.

You're loosing performance, but I don't think you're risking engine damage by putting the repair off. The ECU will put the timing into a worst-case-scenario map to protect the engine, so it's behaving as if it's hearing knock through the sensor.

I have no idea if it will pass your state inspection with the light on... we don't have inspections in SC. My understanding is that most states automatically fail you if the CEL is on, but I don't know for sure about your state.

The part itself is about $100 each. You have two of them, and typically want to replace the subharness and a whole bunch of other hoses while you're in there. I suspect a decent shop would charge you somewhere in the $800 - $1500 range to get it done properly. Where are you located?

There are several threads here on replacing it DIY if you're intertested in going that route...

Heath

Thanks, Heath. I'm in Dallas, TX. I really hope I can pass inspection, 'cause I'm not prepared to spend that much cash for the repair. I checked out the DIY threads which are great, but there's no way I have the time to do this, especially more than once. I'll get back to you about the inspection.
(fingers crossed)

There is a comprehensive thread on here about knock sensor replacement on a VH41DE.

The car will not pass with a CEL, but neither will the KS illuminate the CEL. Have your car scanned and report back.

I will have it rescanned and disclose the exact codes,
Thanks.

OK, here are the codes...
PO400
PO325
I know i can look these up, but any added input would be helpful. I have trouble deciphering service manual lingo sometimes.

P0325 = knock sensor--bank 1
P0400 = EGR system

So I find out that I can't pass state inspection with the CEL.
Are these codes pretty open-ended in terms of interpretation by a mechanic, meaning several hours of diagnosis? Or can they figure it out and repair relatively quickly.

Reset the ECU, drive 50 miles at highway and other speeds, go immediately have it inspected provided no CEL.

I like your style, Brian! Worth a shot.

EGR is probably a clogged passage in the intake. They tend to get caked with carbon - preventing the sensor from reading the hot exhaust gas flowing across the sensor. Not sure how hard it is to clean this on the car on the 4.1 engine, but if you can get to it you might be able to solve that problem.

Heath

Q451990 wrote:EGR is probably a clogged passage in the intake. They tend to get caked with carbon - preventing the sensor from reading the hot exhaust gas flowing across the sensor. Not sure how hard it is to clean this on the car on the 4.1 engine, but if you can get to it you might be able to solve that problem.

Heath

On the VH41DE, it is the EGR valve body and especially the EGR tube in the plenum. The plenum must come off for the latter, and reading the excellent threads by Paranoidjack and Mopar will illuminate with all you need to know.

It ain't pretty but doable if you have all the gaskets on hand and a Dremel with a wand.

EGR is likely rotten rubber hose leading to it-very easy fix-I've done it twice.

Crap! Just picked the car up from the mechanic. That's exactly what it was! Oh well, he only charged $75. Plus he found the cause of my airbag warning light...a disconnected cord under the driver's seat.

My Q45 stumbles a bit when idling but only when its in gear. It idles fine when in park or neutral. It also run fine when driving. My check engine light is on. Codes P0325 P0155 P1168. I have changed the MAF, EGR, air filter, fuel filter, and the spark plugs(NGK). Could a bad knock sensor cause this problem? Any Ideas?

Heath- said the ECU will put the timing into a worst-case-scenario map to protect the engine, so it's behaving as if it's hearing knock through the sensor. Could that cause the stumble and possibly the other codes? I appreciate any help. Thank you

No maintenance history nor mileage cited, but the big money is on the failing coil packs.

Good maintenance and about 120k miles.

bg2327 wrote:Good maintenance and about 120k miles.

Define "good maintenance" please with details of services performed and mileage intervals.

Greetings,

I recently did the KS job, and let me tell you I had the same symptoms as you do right now. Slight miss/stumble when in D, horrible gas mileage, and the car will not move up the hill.

I did a lot of cleaning when I changed my KSs. I am almost 100% sure that those issues are due to bad KS. As you have been told, the computer puts the KSs in fail mode which constantly tells the brain that the engine is knocking. You are basically driving without knock sensors.

I also had problems with my car's breathing. You see, there was so much dirt in the intake manifold, the EGR hard line in the intake was completely blocked! so my engine was barely breathing. I am guessing this killed my gas mileage and partially caused my troubles.

I would suggest if you have the knowledge and the time to do this project yourself. It is not as bad as it looks (even though you will be angry/frustrated at times). You can search Jack's or my thread onto how to tackle the job. The problem with having the mechanic do this for you is that he is not going to go into detail and clean your intake system like it should be cleaned.
Let us know if you want to do the job yourself and we will help you do it. I completed my job solely on the great members pointers and some FSM studying...

After you finish the job you can expect your Q to drive smooth as if it was just rolled from the factory.

bullittandy wrote:EGR is likely rotten rubber hose leading to it-very easy fix-I've done it twice.

Day 4 since I had this fixed. No more CEL. Passed inspection!! No more knock sensor issues!!
Fingers crossed.