Service engine soon

[02_Tahoe]

while doing my 0-60 test a service engine soon light came on. It's come on before and gone away after a few days but this time it's not going away. I don't notice anything wrong with it, still idles the same, no loss of power, it feels the same as when the light was off. Any ideas, maybe a bad O2 sensor? I just want to know if it's still ok to drive until I can go get the code read

 

[David Smith]

Mine just did that a few days ago. I was passing someone and it came on. Got it scanned and it was a knock sensor. After about 3 days the light went back off and has not returned yet. Hopefully it doesn't.

 

[02_Tahoe]

Mine just did that a few days ago. I was passing someone and it came on. Got it scanned and it was a knock sensor. After about 3 days the light went back off and has not returned yet. Hopefully it doesn't.

Idk what that is but it doesn't sound good

 

[David Smith]

It basically tells you motor when it advance or retard your timing from what I understand. You can go to any parts store (Advance, Auto Zone, O'Reilly) and they can scan your truck for free and tell you exactly what it is. Also, maybe have them clear it if they are willing to, and see if it comes back. Mine went off by itself.

 

[02_Tahoe]

It basically tells you motor when it advance or retard your timing from what I understand. You can go to any parts store (Advance, Auto Zone, O'Reilly) and they can scan your truck for free and tell you exactly what it is. Also, maybe have them clear it if they are willing to, and see if it comes back. Mine went off by itself.

I just looked up what it is. Like you said changes timing, and you'll feel a difference in performance, but like I said, nothing is different, it performs the same. And if it's the knock sensor, do I replace the sensor to fix it? Or fix something that caused the knock

 

[David Smith]

Mine did not have a change in performance either. Maybe that is why it went back off after a few days. Might have gotten some bad gas or something. The "knock" is going to happen. The knock sensor is what detects it and makes the necessary changes to the timing. There are 2 knock sensors. You have to remove your entire intake manifold to change them.

If it were me, I would give it another day or two and see if it goes off, or just have someone clear the code (assuming that is what it is) and see if it comes back.

Step one would definitely be to have it scanned and see what the code is anyways. Could be something stupid.

 

[02_Tahoe]

Mine did not have a change in performance either. Maybe that is why it went back off after a few days. Might have gotten some bad gas or something. The "knock" is going to happen. The knock sensor is what detects it and makes the necessary changes to the timing. There are 2 knock sensors. You have to remove your entire intake manifold to change them.

If it were me, I would give it another day or two and see if it goes off, or just have someone clear the code (assuming that is what it is) and see if it comes back.

Step one would definitely be to have it scanned and see what the code is anyways. Could be something stupid.

Man I hope it is something stupid. Although replacing a knock sensor isn't that expensive, I could do it myself

 

[David Smith]

Man I hope it is something stupid. Although replacing a knock sensor isn't that expensive, I could do it myself

It should not be too difficult. There is a lot of stuff to undo, but if you just take your time, it should take more than a few hours.

 

[iamdub]

If the light comes on then goes off, then the problem was a single isolated incident that hasn't reoccurred within a certain number of drive cycles. If it stays, you have a hard failure. Also, if the code defines as "knock sensor signal high/low or O2 sensor signal high/low, etc.", that doesn't necessarily mean that particular sensor is bad. It just means that sensor reported to the PCM something outside of it's allowed/expected normal operating range. Either there is/was a fault and the sensor detected it as it was supposed to do or the sensor is faulty and erroneously reported a fault that didn't/doesn't actually exist.

The the whole OBD thing is not to police the sensors. It's to point you towards the area where you should focus your diagnostics attention. It's up to the person diagnosing it to use all the info available to determine what the problem is, whether it be a "lying" sensor or an actual problem within the system that sensor monitors. Ever heard of "Don't shoot the messenger"? The sensor is the messenger in this sense.

If the light is on and not flashing and the engine is running fine/normal (no sudden drop in power or MPG), then it's probably an emissions code and nothing detrimental to the engine. Plenty of places will scan codes for free, so there's no reason not to at least have this first step done. Just be aware that, especially if you go to Autozone to have the code(s) read, they're very quick to try to sell you whatever sensor(s) the code(s) relate to. Many buy whatever sensor(s), replace them, have the code(s) cleared, then the same code returns. This means either the new sensor is faulty or the problem is not with the sensor, but with the system that the sensor monitors.

Just get your codes read and report back here so hopefully we can help you not waste time and money.

 

[02_Tahoe]

If the light comes on then goes off, then the problem was a single isolated incident that hasn't reoccurred within a certain number of drive cycles. If it stays, you have a hard failure. Also, if the code defines as "knock sensor signal high/low or O2 sensor signal high/low, etc.", that doesn't necessarily mean that particular sensor is bad. It just means that sensor reported to the PCM something outside of it's allowed/expected normal operating range. Either there is/was a fault and the sensor detected it as it was supposed to do or the sensor is faulty and erroneously reported a fault that didn't/doesn't actually exist.

The the whole OBD thing is not to police the sensors. It's to point you towards the area where you should focus your diagnostics attention. It's up to the person diagnosing it to use all the info available to determine what the problem is, whether it be a "lying" sensor or an actual problem within the system that sensor monitors. Ever heard of "Don't shoot the messenger"? The sensor is the messenger in this sense.

If the light is on and not flashing and the engine is running fine/normal (no sudden drop in power or MPG), then it's probably an emissions code and nothing detrimental to the engine. Plenty of places will scan codes for free, so there's no reason not to at least have this first step done. Just be aware that, especially if you go to Autozone to have the code(s) read, they're very quick to try to sell you whatever sensor(s) the code(s) relate to. Many buy whatever sensor(s), replace them, have the code(s) cleared, then the same code returns. This means either the new sensor is faulty or the problem is not with the sensor, but with the system that the sensor monitors.

Just get your codes read and report back here so hopefully we can help you not waste time and money.

The part about the light staying on and not flashing definitely makes me feel better, and mpgs are actually better now because I've been driving it easier with that light on, lol. I can't get to autozone today because I have work after school but I'll go Friday and report the codes. Also glad it's nothing serious because I'm going to the D.C tuning even Sunday for Justin to tune it

 

[iamdub]

It's probably a minor, one-time thing. There are a few possibilities for it to throw a code when the engine's under heavy load/high RPM- detonation, miscorrelation between the MAF and MAP sensors, something in the trans...

Don't have them clear it if you have it read. It may be something Justin should look at and consider before tuning it. Actually, since it's getting tuned, I hope the code(s) is/are still stored so Justin can look at the freeze frame(s).

 

[02_Tahoe]

It's probably a minor, one-time thing. There are a few possibilities for it to throw a code when the engine's under heavy load/high RPM- detonation, miscorrelation between the MAF and MAP sensors, something in the trans...

Don't have them clear it if you have it read. It may be something Justin should look at and consider before tuning it. Actually, since it's getting tuned, I hope the code(s) is/are still stored so Justin can look at the freeze frame(s).

Will he not tune it if there is something wrong with it? If so I hope I can get my deposit back

 

[iamdub]

Will he not tune it if there is something wrong with it? If so I hope I can get my deposit back

That's up to him and what the problem is, but at this point I'm doubting it'll be an issue. Generally, tuning for power includes advancing the timing. If your truck has an issue with detonating (preignition) at higher loads and/or upper RPMs, advancing the timing would make this worse. You may have just gotten some bad gas. Fill up with a top-tier gas of whatever grade of octane you're getting tuned for before you go for the tune. Don't put high octane gasoline in as a diagnostics to this issue if you want it tuned safely for a lower octane level.

There again, your SES light may not have anything to do with detonation or the knock sensor or even the engine. It could be a transmission thing. The ideal thing is to get the code read ASAP, before it is self-deleted. It may go away and the light turn off before you get to Justin, but it would be nice to at least be able to mention the recent issue to him. It could save you a motor and him some headache.

 

[02_Tahoe]

That's up to him and what the problem is, but at this point I'm doubting it'll be an issue. Generally, tuning for power includes advancing the timing. If your truck has an issue with detonating (preignition) at higher loads and/or upper RPMs, advancing the timing would make this worse. You may have just gotten some bad gas. Fill up with a top-tier gas of whatever grade of octane you're getting tuned for before you go for the tune. Don't put high octane gasoline in as a diagnostics to this issue if you want it tuned safely for a lower octane level.

There again, your SES light may not have anything to do with detonation or the knock sensor or even the engine. It could be a transmission thing. The ideal thing is to get the code read ASAP, before it is self-deleted. It may go away and the light turn off before you get to Justin, but it would be nice to at least be able to mention the recent issue to him. It could save you a motor and him some headache.

My trans shouldn't have a problem as it was rebuilt less than 20k miles ago, hopefully this is just something to do with emissions, and I'm on my second tank of gas while having the light on from 2 different stations, so does that rule out the detonation issue?

 

[iamdub]

My trans shouldn't have a problem as it was rebuilt less than 20k miles ago, hopefully this is just something to do with emissions, and I'm on my second tank of gas while having the light on from 2 different stations, so does that rule out the detonation issue?

Not to induce fear or doubt, but transmission techs can and do make mistakes. I highly doubt this is the case, though. I was just listing examples of how things may or may not be related or even pertinent to your tuning.

If you've driven enough miles to burn 2 tanks of gas, then that should be enough drive cycles to clear the code if it was a "soft" failure. If you were having steady detonation issues, especially since driving it easier lately, then you'd definitely have a problem that you'd feel. The problem may not even be a knock sensor issue. It's just the best guess since the light came on during a high load scenario and you say the motor feels normal afterward.

 

[02_Tahoe]

Not to induce fear or doubt, but transmission techs can and do make mistakes. I highly doubt this is the case, though. I was just listing examples of how things may or may not be related or even pertinent to your tuning.

If you've driven enough miles to burn 2 tanks of gas, then that should be enough drive cycles to clear the code if it was a "soft" failure. If you were having steady detonation issues, especially since driving it easier lately, then you'd definitely have a problem that you'd feel. The problem may not even be a knock sensor issue. It's just the best guess since the light came on during a high load scenario and you say the motor feels normal afterward.

I put it under heavy acceleration twice the day before and no light came on. I've had it come on when it was cold after I started it too. Could it just be bad spark plugs?

 

[HiHoeSilver]

I put it under heavy acceleration twice the day before and no light came on. I've had it come on when it was cold after I started it too. Could it just be bad spark plugs?

Stop thinking until you see the codes. You'll just be running in the dark. Don't drive yourself nuts.

 

[iamdub]

^^^ Pretty much what I was gonna say. lol

Also, if you're in doubt about your spark plugs, then you should replace them before the tuning. If they're not old and are the correct ones for your rig, then you shouldn't doubt them. Get your PCM read but not cleared ASAP so you can fix whatever needs to be fixed (if it needs it) before getting it tuned. You gotta at least know why your SES light is on.

We could speculate and guess all day long but all that's gonna do is stress you out.

 

[02_Tahoe]

Stop thinking until you see the codes. You'll just be running in the dark. Don't drive yourself nuts.

Too late

 

[02_Tahoe]

^^^ Pretty much what I was gonna say. lol

Also, if you're in doubt about your spark plugs, then you should replace them before the tuning. If they're not old and are the correct ones for your rig, then you shouldn't doubt them. Get your PCM read but not cleared ASAP so you can fix whatever needs to be fixed (if it needs it) before getting it tuned. You gotta at least know why your SES light is on.

We could speculate and guess all day long but all that's gonna do is stress you out.

I have enough time after work so I'll go get that checked