Strange Check Engine Light Condition

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  #1  
Old 11-13-02, 05:20 PM
rckowal1
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Strange Check Engine Light Condition

Hi Guys,

I posted this condition before but the problem still isn't resolved. Car is a 1998 Pontiac Grand Am with the 2.4L 4 cylinder engine. Has 80,000 miles & auto transmission.

The check engine light is definitely intermitent. It will come on for short time & then stays off most of the time. It never stays on for long periods. In fact, although it doesn't make much sense to me, it appears to go off when the fuel tank is filled & comes back on when the tank level drops to near 1/4 full. It's done this at least 3 or 4 times now during several weeks of driving.

For what ever it's worth, it's had the "freebie" diagnostic checks at Autozone twice now with inconsistent codes being reported. Three weeks ago the codes reported were PO134 = bank 1, O2 sensor. The other was PO 125 = low coolant temp (probably not driven long enough to thorougly heat up the engine).

Today, with the tank setting at 1/4 full & the engine light on, they reported "1133 (Manufacturer special code) = Insufficient switching sensor, Bank 1. Fuel control shifted lean"! I filled the tank & after driving for about 10 miles the light went off.

Can anyone explain what's happening here before I take it back to my mechanic again? The last time he said to drive it until the light comes on & "STAYS ON" which it hasn't. He said he can't diagnose a condition that doesn't exist (while the engine light is off).

Your help will be appreciated.

Best regards, Dick
 
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  #2  
Old 11-13-02, 05:40 PM
otter_
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sounds like you might have a mis-firing injector(s) due to crud in the bottom 1/4 of your tank making it into your fuel system. Might want a pro to do a proper injector purge and replace the fuel filter. (not a bottle of STP dumped into your fuel tank)

Your mechanic should be able to extract historic codes from the computer as this is an OBDII vehicle.
 
  #3  
Old 11-13-02, 05:52 PM
davidf
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Low temp code is usually caused by a bad connection on the temp. sensor on the thermostat housing or the sensor is bad.The sensor is the copper color bullet with 2 wires attached to it.One wire is computer ground which is separate from chassis ground.Disconnector connector and clean it and check for broken wires or intermittent connection.Connect voltmeter across the two wires and for a cold engine , you should read 5 volts ..The computer interprets the 5 volts as cold engine condition and squirts more fuel from injectors.Lower than 5 volts,change the sensor.
 
  #4  
Old 11-13-02, 05:52 PM
Joe_F
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Thumbs up

I agree with Otter.
 
  #5  
Old 11-13-02, 05:53 PM
rckowal1
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Hi Otter,

Thanks for the reply. Interesting, I never considered anything of that sort. Of course, I'm not a mechanic so why would I???

I'll suggest that to my mechanic when I explain what all we've been seeing since our last visit to his shop.

Best regards, Dick
 
  #6  
Old 11-13-02, 05:55 PM
rckowal1
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Also thanks to David & Joe for their inputs.

Best regards Guys, Dick
 
  #7  
Old 11-13-02, 06:57 PM
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Join Date: Apr 2002
Location: Pittsburgh,Pa
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You have 2 codes that suggest the o2 sensor and one for coolant temp.I think you have a bad o2 sensor and either low coolant or a bad thermostat.Its also possible to have a bad pressure regulator set the o2 codes or a fuel laden evap system.Do you top off your tank when the pump shuts off?no no don't do that on todays cars with obdII.You also could have a pcm ready to die(engine computer)I've looked up ypur codes.Pick one to do first,you will need a scan tool to keep from replacing parts you don't need.I'll send you diagnostic charts as needed.
 
  #8  
Old 11-14-02, 07:10 AM
otter_
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more specifically

P0134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control


Ok, definately look for a bad connections or bad sensors themselves. But I still think that it's a good idea t purge the injectors and replace fuel filter if it hasn't/no record of it being done recently. I'm only suggesting the purge and replace as you state that trouble starts showing up when you get down to 1/4 of a tank.
 
  #9  
Old 11-14-02, 07:15 AM
otter_
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FYI, check it out.

http://www.obdii.com/obdii.html
 
  #10  
Old 11-14-02, 08:06 AM
rckowal1
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Otter & Davo,

For one thing I'm guilty of topping the tank when filling. I'll stop that now that I know better.

There is no question that the engine light comes on as the fuel level drops. It's done so repeatedly for 3 or 4 fillups/drops now. In fact, it's the only symptom/sign that has repeated itself. Since I've only owned this car for a month or so, I don't know it's history. I doubt that it was maintained well enough that the prior owner would have had the fuel filter changed & injectors cleaned.

So far, all of the other error codes have been a one time event (without ever repeating). I could be wrong but this seems to strongly suggest that the fuel level symptom is directly linked to this condition. Otherwise, why wouldn't the O2 sensor or temp code repeat when the light is on during the diagnostic test? Since they never repeated, my logic says the O2 sensor code might have been the result of me over-filling the tank.

Best regards & thanks again, Dick
 
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