Q45 Check Engine Light

[pmcd1966]

My plenum saga continues...

Got the car running after a lengthy plenum job to fix a coolant leak. Now my check engine light is on. Took the car to Advance Auto Parts and they checked the ODB II codes:

P0100, MAF or VAR Circuit MalfunctionP0505, Idle Control System MalfunctionP0325, Knock Sensor 1 Circuit Malfunction Bank 1 or Sensor 1

The check engine light wasn't on before I did the plenum work. The guy at Advance suggested that the MAF issue may be causing the other 2 codes.

Is there any way to check the MAF (short circuit the connector?) or any of these other issues?

Patrick

[elwesso]

I think if it were my car i would have thrown up knowing that the KS are bad and you eventually gotta do em again!

Did you plug back in the IAC... On the 96 you cant adjust them so thats all good...

Not really sure what to say about the MAF, except that you need to swap it out with a known good one. If the code goes away, case closed. If it stays, that means the connector is bad.... However, it could be a combination thereof....

[squeefoo]

Clean off the MAF harness connector, or reground it. Do a search here. Real bummer on the KS -you probably have to R & R the plenum, could be the harness and/or the sensors, on the bright side it'll go faster this time. Call Joe for the best price. Not sure on the idle control prob.

[pmcd1966]

I find it hard to believe that taking the plenum off would cause three distinct issues like this. No problems before I did the work and now three! It doesn't make a lot of sense unless there is a connection issue or the MAF is dirty or something (it was sitting out exposed to dust, etc. for a week) and that's having a cascading effect. I'll try cleaning the MAF first and see what happens. Wes is right - if the KS ARE bad, then the hurling will commence. They looked good when I had the plenum off though.

[DAEDALUS]

The KS code probably isn't related to the other 2. Did you check the codes before the job? You could have had bad KS for a while, since they won't turn on the MIL while throwing a code. Still kind of sounds like an air leak. Air that gets in past the MAF goes unmeasured--by the MAF--but shows up in other places...RPM, HO2S, and frames the MAF for a crime it didn't commit. Also make the idle control system look bad too, doesn't it. Leaking air can be a stealthy criminal.

[Q45tech]

Always remember you only get a KS code when the startup or periodic check show that 1 or more sensor is not working correctly.It has the wrong resistance or is not generating a microphonic signal during the narrow ecu gate open time window 20 degrees every 90 degrees.

[brette10]

If you have a bad knock sensor (reading open (Ohm)) does this keep the check engine light on? I need to pass smog here in california and I have one bad fuel injector (open)easy to get to, and one bad knock sensor(hard to get to), and check engine light is on. if I replace the one injector and clear the ecu will the bad knock sensor keep the check engine light on?the smog tech said if check engine light is on it fails smog test for visual part, not the actual tailpipe output test.so does a bad KS keep check engine light on? thanks guys Brett

[Q451990]

You might snag your FSM (Factory Service Manual) here to see if it's an item that will trigger the check engine light. http://www.iposer.com/TBO/Niss...20Q45/

It's not exactly uncommon for questionable knock sensors to fail right after a plenum job - especially if you get a lot of antifreeze and gasoline contact with the connector. Look at the bright side - at least the hoses will be easier to remove sine they're nice and soft.

Heath

[pmcd1966]

It turns out that the check engine light was showing codes that occurred when I first started the engine and had a plenum gasket misaligned. The engine ran horribly of course until I identified the problem (with Wes' help!). Fortunately I live close to T3, and the wonderful people there reset the ECU and told me that if the light didn't come back on then I'm in the clear. So far, the light is still out so it looks good.

[elwesso]

It turns out that the check engine light was showing codes that occurred when I first started the engine and had a plenum gasket misaligned. The engine ran horribly of course until I identified the problem (with Wes' help!). Fortunately I live close to T3, and the wonderful people there reset the ECU and told me that if the light didn't come back on then I'm in the clear. So far, the light is still out so it looks good.

Really, I helped someone...

Glad you got it going though... Simple things will kill you like that..... Did you reuse the metal rings that go inside the plenum gaskets???

[Q45tech]

In the almost 15 years of owning my 90 Q, never has the check engine light come on after the initial start up test. At 200k [10 years] the knock sensor failed after as plenum hose [second set] replacement.

These things happen every 5-6 years or 70-120,000 miles or combo thereof.

Just part of the owning experience- "own one and you'll understand" was a dropped slogan from years ago.............more profound than they knew at the time..............that you might need a second part-time job to keep the Q up.

[pmcd1966]

I think I'm beginning to understand...

The metal rings and gaskets weren't damaged. The car is still running great.

[DAEDALUS]

Meaning you reused the gaskets? They must feel like hard plastic, not the soft rubber when new. Might be worth the $25 cost to reduce the likelihood of such leaks.

[Q451990]

I always replace the gaskets, but I don't see any reason the rings can't be cleaned and reused....

Heath

[elwesso]

I reused my rings.....

It does say in the FSM that you dont have to get new gaskets.. IE you can reuse them... If you look at the OUTER COMPONENT PARTS diagram, theres not an X around where the plenum gaskets are.....

Id replace em anyway, its only like $10 for all 8.....

[DAEDALUS]

If they're leaking they should not have been reused. I'll wager it's a mistake there's no x callout in the diagram. How many gaskets are reusable, especially after this many years?

[elwesso]

If they're leaking they should not have been reused. I'll wager it's a mistake there's no x callout in the diagram. How many gaskets are reusable, especially after this many years?

True, and like I said, i wouldnt want to reuse.. Just stating that technically speaking you can! Mine were very brittle and gooey when i took them out, and the new ones were soft and pliable...

[DAEDALUS]

Technically you can do whatever you want when you work on your vehicle. But common sense should supersede whatever the shop manual says. Otherwise a few of us might be tempted to raise the front of the vehicle by the oil pan!

"brittle AND gooey"?

[pmcd1966]

I used new gaskets. My problem was that one of them wasn't seated correctly when I started the car. I guess it moved when I was aligning the plenum. Once I found the problem I was able to move the gasket into place and re-torque the plenum. You really want to replace every hose/gasket when you do this.

[mixatonia]

At 200k [10 years] the knock sensor failed after as plenum hose [second set] replacement.

Once in a while my q45 knocks no matter what gas I give it. Then it goes away. It seems to be related to winter weather but I cant prove that since I dont keep statitsics. Could be the gas for all I know as I do not know much about knock.

It may be in a nother forum so I apologize a head of time but how can I know if my knock sensor (only one?) has failed? Would it be intermitant like I am seeing?

[Q45tech]

When the knock sensors fail you go into reduced advance mode [should tolerate best regular grade fuel with power and economy losses] if it is indeed the functional equivalent of 87-89 blended octane.

Unfortunately in Winter the refineries know they can get by with less so they blend more cheaply...........while the average may still be 91 octane the critical motor octane points are replaced with more research octane points which are useless in a high performance engine...........thus the winter knock.

Also the tip in A/F ratio assumes 60F so the denser/colder winter air will make for a momentary extra lean [knock promoting] situation.

The use of splash blending [adding 10-12% ethanol at the local tank farm] means they can ship real garbage gasoline [and get a 1-2 octane point] bump up ...............but I'll bet most 91 pump labels will be more like 89 in winter even with ethanol as it cost close to a penny an octane point [blended] and 2.3 cents for a 1 point rise in motor octane [from gasoline alone].........per gallon.

In these days of garbage fuel ------knock sensors are even more important.Saving 5-10% in fuel cost [$200 per year] can be an easy 4-5 year payback

$450 every 6-7 years for KS replacement [while doing under plenum work] is easily offset by fuel cost saving. Same with O2 sensors.They pay for themselves now that gaoline is $2.

I understand the validity of paying weekly in gasoline [extra cost] vs. lump sum repairs but you must take the long term view if you plan on keeping the Q/J for at least 5 more years.