Phantom Check Engine Light/Rough Engine/Coolant Temp. Gauge Whacky - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 11-11-2009, 01:41 PM   #1
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Default Phantom Check Engine Light/Rough Engine/Coolant Temp. Gauge Whacky

First post here, by no means a car guy...so go easy on me.

1998 Bonneville SE with just over 144,000 miles. New MAF sensor a year ago, new upper intake manifold and gaskets in July.

First issue, I have a "phantom" check engine light. Will come on bright and steady for a week, then shut off for a couple of days. Come on bright and steady for a couple of days, and then shut off for a couple of days. Repeat. When I got my MAF sensor replaced my mechanic said that I would eventuaklly need a new O2 sensor. I have no idea if this problem with the check engine light is related to the O2 sensor or not.

My engine runs a bit rough, for a few seconds, from time to time as I accelerate out of a stop light. Recently, once the car is up to speed, I have had the engine quit completely. Seems to happen about once a week. Very odd. I don't know if this is a "misfire" issue or if this is something directly related to my check engine light as the check engine light has only been triggered after one of the "stalls." I'm baffled on this one. MAF sensor going bad again? O2 sensor taking a crap? Bad fuel pump/fuel injectors? Ideas?

Had my upper intake manifold and gaskets replaced in July as the engine was overheating. Turned out the culprit was a small hole in the UIM. Temp.-wise the car has been running fine until a few nights ago. Noticed that the temperature gauge fluctuates between the "200" hash mark and the hash mark right before the red, "over heat" region on the gauge in the dash. It'* not overheating, but I have never seen a wild fluctuation like that before. It also only appears to be happening when the car is idling. When the car is in drive and I am moving down the road, the needle in the guage appears to retreat back down to the "200" hash mark. Is this normal? Faulty thermostat (even though my mechanic claims that he replaced my old one when he replaced my UIM and gaskets)? Cooling fans not working like they're supposed to?

Quite a few problems for a first post! Any help/insight that can be offered is greatly appreciated.

Thanks!
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Old 11-11-2009, 01:46 PM   #2
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Actually it'* most likely all related. Glad to see you list it all in one place instead of trying to break it up. Breaking things up or not mentioning other symptoms is like witholding relevant info.

Let'* start you off with heading to Autozome/Advance or whereever locally will check codes for free. Please write down the code numbers and then post them here. That will explain the check engine light and most likely the other issues.

From there we can help you determine what each code actually means with your car and which items should be fixed. Please do not buy anything when they scan your car. 90% of the time the part you buy does not fix the issue.

See ya soon.
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Old 11-11-2009, 01:47 PM   #3
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Need the car scanned for the code, that will help. A misfire will flash the SES light, not stay on steady. From the limited info you have given I'm leaning towards a throttle position sensor, but that may change with more info. Another possibility is a vacuum leak.
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Old 11-11-2009, 01:48 PM   #4
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I would start by going to Autozone and having them scan the car for Diagnostic Trouble Codes.
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Old 11-11-2009, 01:49 PM   #5
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As for the temp gauge, that sounds like you have air in the cooling system. Check the coolant level in the radiator, when cold.

You also mentioned the car cut out, check the battery cables for corrosion.
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Old 11-12-2009, 05:24 PM   #6
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Go the local AutoZone today and had them pull the codes that are apparently giving me trouble.

Got a P0336 and a P0442. The P0336 appears to lead to a crankshaft senor issue. The P0442 code claims to be a "evaporative emission system."

Looks like a crank sensor is going to run me about 25 dollars. Got a quote from a shop in town and they said that they would do some sort of "smoke test" to pinpoint the location of a leak.

No parts have been bought, no labor charges have been paid.

Sound like I am off on the right foot so far?
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Old 11-12-2009, 05:53 PM   #7
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Quote:
Originally Posted by RWW2003 View Post
Got a quote from a shop in town and they said that they would do some sort of "smoke test" to pinpoint the location of a leak.

Are you looking to find an exhaust leak?
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Old 11-12-2009, 06:05 PM   #8
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Not sure, to tell you the truth. The little ticket that AutoZone printed me out for the P0442 code says:

1. defective or loose fuel cap.
2. EVAP cannister or hose cracked-not connected.
3. Purge or vent solenoid defective.
4. Vacuum leak at engine.

Not sure what sort of test the guy I spoke to on the phone was speaking of, but he said that it was a test, involving smoke or pressure or something, that would allow them to see if there were any leaks around the engine that would cause this code to register.

Hoping it'* something as easy as a faulty fuel cap or something...

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Old 11-12-2009, 06:33 PM   #9
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You can check for a vacuum leak by spraying carb cleaner around the engine bay at the vacuum lines, fitting, connections, etc. With the car idling in park, a change in idle speed when you spray a particular area is sign there is a vacuum leak that is picking up the spray. One susceptible area is around the EGR.
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Old 11-12-2009, 10:02 PM   #10
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