Check Engine Light Results


Old 10-16-02, 04:39 PM
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Check Engine Light Results

I need some help with this situation please. Vehicle is a '98 Pontiac Grand Am 4 cylinder with 78,000 miles. Engine light came on & stayed on however, it went off after the diagnostic check was done.

Autozone checked & reported two OBD codes. P0134 = O2 sensor and P0125 = Insufficient coolant temperature loop fuel control.

They were pretty sure about the O2 sensor being bad but not sure what exactly the P0125 meant. They also suggested that this code might go away when the O2 sensor is replaced.


1. I understand that the O2 sensor is in the exhaust manifold forward of the catalytic converter. Is this some thing that a handy DIY selfer can replace? Autozone will loan me the special wrench needed but couldn't tell me if the sensor can be readily serviced from under the hood or from under the car. It's a $19.00 part.

2. Is this an urgent condition requiring immediate replacement? Or can it wait a week or two - maybe 400 miles?

3. Can anyone provide additional insight regarding the P0125 code? What might cause it & what needs to be done to fix it?

Your assistance will be very much appreciated.

Best regards, Dick
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Old 10-16-02, 05:22 PM
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There are multiple O2 sensors on this vehicle (pre and post catalyst) and you should change them all.

Check below in my signature file to see what's involved in changing them.

Anything that sets the check engine light needs to be rectified right away as eventual damage to the vehicle can occur. OBDII is much more sensitive to codes and problems than their OBDI counterparts.

Change the O2 sensors and bring it back to be rescanned and have the codes reset by them (they use the scanner to do this). The other code could be related to the coolant temperature sensor.
Old 10-16-02, 05:44 PM
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Hi Joe, Thanks for the reply, it's appreciated.

I tried the link autolibrary & cyberparts pro. Neither opens into a web site - only a message that they're not available or some such note.

So, from that, I still have no idea where exactly the O2 sensor can be found on this car. I have Autozones instructions on how to do it but where do I find it?

Best regards, Dick
Old 10-16-02, 07:02 PM
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You can change the #1 O2 sensor under the hood.It's located betwwen the engine cover and the firewall in the exhaust manifold.On the other code I would try a themostat,but they are not easy on a 2.4 engine.You could try a coolant sensor for the pcm.I would change the O2 sensor as soon as possible to try and avoid convertor damage.
Old 10-17-02, 05:41 AM
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You have to use the autolibrary link (cut and pasted) AS I have it or it will not work.

The link works, I used it yesterday.
Old 10-17-02, 07:42 AM
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Joe F & Davo,

Thanks guys for the replies - they're appreciated.

Joe, that Chilton site must be having problems. When I tried it this morning, it connected & asked me to enter the year & model. I entered 1998 Grand Am, hit enter & it went to another page that showed various engine & model options. I checked on the 2.4L model. Looking around the page, the only button shown says "BACK". I click on it & I'm back to the 1998 Grand Am page to repeat the process.

Or, am I missing something????

Best regards, Dick
Old 10-17-02, 05:37 PM
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I used it this afternoon at work to show a coworker and it worked out fine .

We looked up a 1992 Grand Marquis 4.6L.

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Old 10-28-02, 06:28 AM
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Oe Sensor Update

Hi Guys,

I need some more advice regarding the mis-behaving O2 sensor. Your assistance will be much appreciated.

Just after the above posts, the "Check Engine" light went out by itself. Two reliable mechanics suggested that I bring the car back when the "Check Engine" light comes on & stays on - because they can't accurately diagnose what isn't there when they check it.

The car has been driven for about 10 days now with no driving or starting issues (runs & starts just fine). However, the "Check Engine" light has become intermitent. It will come "ON" for a day (plus or minus) & then go "OFF" again. One time, it appeared to go "OFF" when I slammed the hood closed.

This is leading me to think that this condition may possibly be due to a faulty electrical connection at the end of the sensor wire (electrical intermitant) rather than a faulty sensor.

I intend to check & clean that connection; but before I do, does anyone have any other ideas to offer about what's going on here?

Do O2 sensors become intermitant internally? In other words, inside the sensor (rather than the electrical connector at the end of its wire lead).

Best regards, Dick
Old 10-28-02, 07:36 AM
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The O2 sensors are likely lazy at this stage of the game.

That can be checked by a mechanic using a good scanner.

At this stage of the game, I would pitch both O2 sensors, reset the light and be done with it .
Old 10-28-02, 10:25 AM
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I'd take a look at the thermostat. P0125 simply means that the engine did not reach operating temp. within a preset time limit. When that happens, the PCM can set *false* O2 codes.

The thermostat is cheap & easy to replace, so I'd start there. Then clear the codes & drive it for a while.
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