mystery check engine light

Fazed Out · 01-02-2007, 08:03 PM

I was driving along Friday and suddenly the check engine light came on. I pulled over and checked things out, but nothing seemed to be amiss. I checked it again Saturday and the oil level as well as coolant were fine (although I have air bubbles in the coolant causing a bouncy idle, but that’s never caused a check engine light before). I didn’t notice any unusual sounds or exhaust emissions, either. I can’t actually find anything wrong with the car, but the light is still on today as I drove to work (as a test). The light is immediately on when I turn the engine on, and stays constant until I turn it off.

I changed the oil about 200 miles ago, and its still real clean (new filter too). The only other strange thing (this may not be related) is that if the car has been sitting for a few hours; I.e. overnight or after work, the oil light comes on on startup and turns off after about 1-2 seconds (never comes back on). I figure that its just taking a second to get the oil up there (its in the ballpark of 30-40F here, so I was assuming its warming up or something else non-threatening).

That’s a pretty vague description, I know, but are there any particular problems that would cause only the check engine light? Perhaps there’s a bad sensor somewhere. Where can I get something to decode what that means? I’d sure like to fix whatever its telling me is wrong. Anyone experience that kind of thing before, or able to offer any advice?

V6'er · 01-02-2007, 08:32 PM

Let's start with an absolute un-truth: bubbles in the coolant do NOT cause a bouncing idle. The thermal sensor in the throttle body simply can't respond that fast.

So, this means that your bouncing idle has another cause. And, it might be severe enough to cause a CEL, although I doubt that actually.

You can read the CEL codes by shorting the T1 and TE1 connections in the Diagnostic connector in the engine bay. (Key ON, not running.)

You cound the codes after the long pause.

Luni · 01-02-2007, 08:52 PM

Coolant temprature sensor could cause this.

I dont necessarily think the bubbles could make the thermocoupler respond that fast, however I do know from experience if your sensor is loose or on its way out (the plastic breaks off of the metal coupler where it screws into the coolant neck), it can cause that.

And Ive also found from experience that just pulling a check engine light for a second wont casue the code to get stored in memory.. Ive pulled a CEL for no reason, turned car off, back on, and lost the code. Meaning when I pulled the codes by using the jumper, it has no codes stored.

V6'er · 01-02-2007, 09:01 PM

Quote:

Originally Posted by Raven

The light is immediately on when I turn the engine on, and stays constant until I turn it off.

You get a code, we'll get a BGB description for you.

Fazed Out · 01-03-2007, 01:38 AM

I'm not sure that it is related to the bouncing idle. The back story to the coolant is that I had a leaking radiator (replaced that with a new one) and after bleeding the air out of the system, the bouncing completely stopped. What I did wrong is take the two little screws out of the bottom (which had rusted) and they weren't able to get a solid seal again, and slowly leak out coolant. After a while, the bouncing comes back, and I can open the rad cap and see the low coolant level in the tube. Fill it up, bleed it, and no more bouncy needle. This has been par for the course for about a half year (as soon as I get the time and good weather I'm fixing that, too). At no point has it ever caused a CEL. If the sensor has been gradually going out and causing this, that'd be a wonderful blessing! I've yet to have a "little" problem resolved for less than $300. I guess when I say "bubbles" I don't mean little tiny ones, but perhaps one or two large ones.

But this oil light coming on has been within the past 200 miles or so, which is fairly close to the start of this CEL. What worries me is this is a big, oil-related thing.

But enough about all that. Its all conjecture until I count the codes (a handy trick I did not know about). I'll do it after work and let you all know what it says. Thanks guys!

Fazed Out · 01-04-2007, 02:48 AM

Ok, after checking the diagnostic port with a paper clip, I appear to have a code 21. Does that shed some light on anything?

Luni · 01-04-2007, 03:50 AM

21 is O2 sensor signal heres what the BGB says

"During air-fuel ration feedback correction, voltage output from the O2 sensor does not exceed a set value on the lean side and the rich side continuously for a certain period.

Or a Open or short in o2 sensor heater"

Good luck.

Fazed Out · 01-07-2007, 09:09 PM

That's exactly what it was... new O2 sensor from Autozone and I'm right as rain. Only took about 5 mins, too. Thanks everyone for your help!

01-02-2007, 08:03 PM	#1 (permalink)
Fazed Out I'll write your name Join Date: Feb 2005 Location: Tulsa, Ok Posts: 369 Thanks: 5 Thanked 6 Times in 6 Posts iTrader Rating: (0/0% )	mystery check engine light I was driving along Friday and suddenly the check engine light came on. I pulled over and checked things out, but nothing seemed to be amiss. I checked it again Saturday and the oil level as well as coolant were fine (although I have air bubbles in the coolant causing a bouncy idle, but that’s never caused a check engine light before). I didn’t notice any unusual sounds or exhaust emissions, either. I can’t actually find anything wrong with the car, but the light is still on today as I drove to work (as a test). The light is immediately on when I turn the engine on, and stays constant until I turn it off. I changed the oil about 200 miles ago, and its still real clean (new filter too). The only other strange thing (this may not be related) is that if the car has been sitting for a few hours; I.e. overnight or after work, the oil light comes on on startup and turns off after about 1-2 seconds (never comes back on). I figure that its just taking a second to get the oil up there (its in the ballpark of 30-40F here, so I was assuming its warming up or something else non-threatening). That’s a pretty vague description, I know, but are there any particular problems that would cause only the check engine light? Perhaps there’s a bad sensor somewhere. Where can I get something to decode what that means? I’d sure like to fix whatever its telling me is wrong. Anyone experience that kind of thing before, or able to offer any advice?

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01-02-2007, 08:32 PM	#2 (permalink)
V6'er All Torque, All the Time Join Date: Apr 2005 Location: Charlotte, NC Posts: 830 Thanks: 0 Thanked 20 Times in 14 Posts iTrader Rating: (1/100% )	Let's start with an absolute un-truth: bubbles in the coolant do NOT cause a bouncing idle. The thermal sensor in the throttle body simply can't respond that fast. So, this means that your bouncing idle has another cause. And, it might be severe enough to cause a CEL, although I doubt that actually. You can read the CEL codes by shorting the T1 and TE1 connections in the Diagnostic connector in the engine bay. (Key ON, not running.) You cound the codes after the long pause.

01-02-2007, 08:52 PM	#3 (permalink)
Luni ST185 Powered SW20 Join Date: Oct 2005 Location: Salt Lake City Utah Posts: 2,740 Thanks: 7 Thanked 95 Times in 81 Posts My Google Map iTrader Rating: (8/100% )	Coolant temprature sensor could cause this. I dont necessarily think the bubbles could make the thermocoupler respond that fast, however I do know from experience if your sensor is loose or on its way out (the plastic breaks off of the metal coupler where it screws into the coolant neck), it can cause that. And Ive also found from experience that just pulling a check engine light for a second wont casue the code to get stored in memory.. Ive pulled a CEL for no reason, turned car off, back on, and lost the code. Meaning when I pulled the codes by using the jumper, it has no codes stored.

01-03-2007, 01:38 AM	#5 (permalink)
Fazed Out I'll write your name Join Date: Feb 2005 Location: Tulsa, Ok Posts: 369 Thanks: 5 Thanked 6 Times in 6 Posts iTrader Rating: (0/0% )	I'm not sure that it is related to the bouncing idle. The back story to the coolant is that I had a leaking radiator (replaced that with a new one) and after bleeding the air out of the system, the bouncing completely stopped. What I did wrong is take the two little screws out of the bottom (which had rusted) and they weren't able to get a solid seal again, and slowly leak out coolant. After a while, the bouncing comes back, and I can open the rad cap and see the low coolant level in the tube. Fill it up, bleed it, and no more bouncy needle. This has been par for the course for about a half year (as soon as I get the time and good weather I'm fixing that, too). At no point has it ever caused a CEL. If the sensor has been gradually going out and causing this, that'd be a wonderful blessing! I've yet to have a "little" problem resolved for less than $300. I guess when I say "bubbles" I don't mean little tiny ones, but perhaps one or two large ones. But this oil light coming on has been within the past 200 miles or so, which is fairly close to the start of this CEL. What worries me is this is a big, oil-related thing. But enough about all that. Its all conjecture until I count the codes (a handy trick I did not know about). I'll do it after work and let you all know what it says. Thanks guys!

01-04-2007, 02:48 AM	#6 (permalink)
Fazed Out I'll write your name Join Date: Feb 2005 Location: Tulsa, Ok Posts: 369 Thanks: 5 Thanked 6 Times in 6 Posts iTrader Rating: (0/0% )	Ok, after checking the diagnostic port with a paper clip, I appear to have a code 21. Does that shed some light on anything?

01-04-2007, 03:50 AM	#7 (permalink)
Luni ST185 Powered SW20 Join Date: Oct 2005 Location: Salt Lake City Utah Posts: 2,740 Thanks: 7 Thanked 95 Times in 81 Posts My Google Map iTrader Rating: (8/100% )	21 is O2 sensor signal heres what the BGB says "During air-fuel ration feedback correction, voltage output from the O2 sensor does not exceed a set value on the lean side and the rich side continuously for a certain period. Or a Open or short in o2 sensor heater" Good luck.

01-07-2007, 09:09 PM	#8 (permalink)
Fazed Out I'll write your name Join Date: Feb 2005 Location: Tulsa, Ok Posts: 369 Thanks: 5 Thanked 6 Times in 6 Posts iTrader Rating: (0/0% )	That's exactly what it was... new O2 sensor from Autozone and I'm right as rain. Only took about 5 mins, too. Thanks everyone for your help!