• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

CEL on my mom's eclipse.

Status
Not open for further replies.
Raduque

Raduque

Lifer
Had a problem with the CEL on my mom's car. Pulled the code, was a bad upper O2 sensor (front bank). We replaced the O2 sensor, pulled the battery cable and reset the ECU, left it off for 15-20 minutes.

Car was fine after the first start, ran rough/wouldn't idle as they do when the ECU's reset, but cleared up within about 20-25 minutes and runs fine.

The second time the car was started - within the first 5 minutes of running, the CEL came on. Pulled the code again and now it says BOTH O2's are bad. Even the one we just replaced. The engine runs great, however. The first time it threw a CEL about the O2 sensor, it ran like crap. Stuttering, hesitation, hunting for idle, wouldn't idle with the AC compressor on, etc.

We just had Autozone clear the code and it was fine the first time she started after that, but the second time - CEL came on after 5 minutes again.

Cleared the code by pulling the battery cable again, and the cycle repeats. Fine for the first start, 20-25m to run right, second time car is started, 5 minutes later, CEL. Same code, both O2's.

I don't know what's going on. Could both O2 sensors be bad even though the engine is running fine?
 
Could be. Change the 2nd one out and see how it goes. When the O2 sensor went out on my old 96 Galant, I changed them both.

I had to change the sensor on my GLi because squirrels/rats ate the damned wire. lol
 
I don't have the actual code number, but I read the screen on the OBDII tool. It said something like "bad O2 sensor, bank 1, cyl 1 upper; bad O2 sensor, bank 1, cyl 1 lower". "Upper" is the pre-cat sensor, and lower is the post-cat sensor. I believe this car only has one cat and two O2's, which are only on the front bank of cylinders (1,3,5).

When the first O2 sensor was actually bad, the car ran like crap. The car runs great now, even with the "bad O2 sensors" code.

Edit: It's a 2002 Eclipse GT with the 3l V6 and a manual transmission, 96k miles and the plugs and wires have been replaced once since we owned it (purchased in 2005 with a little over 60k on the clock).
 
Last edited:
Raduque said:
I don't have the actual code number, but I read the screen on the OBDII tool. It said something like "bad O2 sensor, bank 1, cyl 1 upper; bad O2 sensor, bank 1, cyl 1 lower". "Upper" is the pre-cat sensor, and lower is the post-cat sensor. I believe this car only has one cat and two O2's, which are only on the front bank of cylinders (1,3,5).

When the first O2 sensor was actually bad, the car ran like crap. The car runs great now, even with the "bad O2 sensors" code.

Edit: It's a 2002 Eclipse GT with the 3l V6 and a manual transmission, 96k miles and the plugs and wires have been replaced once since we owned it (purchased in 2005 with a little over 60k on the clock).
Click to expand...
I have an idea.

Where do you live?

Not sure about where you are but here crappy winter gas can cause intermittent CELs for O2 sensors. Its happened to me twice. My O2 is fine but will occasionally throw a code P1131 which is "upstream O2 lean". It then goes away the next day or with a higher quality gas fill up. This was happening on regular 87 gas but not on 91.
 
there is no 'bad o2 sensor' code. you're diagnosing the car like you work at autozone- just because the code definition has the name of a part in it, does not mean to replace that part. get the actual DTC.

you should have four o2's, as mentioned. and even if they were completely inoperative, they should not cause the engine to run (very) poorly. it will simply run in open loop, using a less efficient fueling strategy derived from the rest of the sensors (MAF, ECT, et al).
 
There is a possibility the O2 sensor you bought at AutoZone is bad too. They don't always sell the right part, especially for sensors in imports. Just because it fits doesn't mean that it's sending the right signal to the ECU. An OEM sensor would have been a better choice for your vehicle if you were certain that it was a bad sensor.

OBDII diagnostics are actually pretty spot on, if it says the O2 sensor is bad, it's bad. The problem is there are codes that, in English, sound like a bad sensor but what's really implied is that the sensor is reporting a condition that is out of whack and is sensed at an O2 sensor. The problem could be a leaky gasket, a failing fuel injector, or a host of other problems un-related to the O2 sensor.
 
For the sake of example, let's simplify this. Pretend there is one O2.

So, what's involved in regards to that O2 sensor? There is the sensor itself, there are wires, there are various connectors, there is the computer and there is a ground. The computer detects a problem regarding the O2 sensor and it turns on the CEL. So, where is the problem? It could be any of the components I listed.

You could start pulling apart connectors and carefully examine the contacts. It takes very little 'corrosion' to start giving bad information. I put corrosion in quotes because you may not even recognize it as such. If you see even a little wisp of white powder on a connector, you may have found your problem.

This is a seat of the pants statement, but 99 times out of a hundred, the problem is the sensor. When it's not, is when it gets challenging.

Now don't misunderstand and think I'm telling you that you have a bad connector somewhere. This was an example. The point of my post is that it's not always the sensor. You're going to have to examine the connectors, the wiring and make sure your grounds are good. You're going to eliminate possible causes one by one. This may take more diagnostic ability than the average Joe possesses. It may take a wiring diagram, a multimeter and maybe a helper.

My $.02.
 
kornphlake said:
OBDII diagnostics are actually pretty spot on, if it says the O2 sensor is bad, it's bad. The problem is there are codes that, in English, sound like a bad sensor but what's really implied is that the sensor is reporting a condition that is out of whack and is sensed at an O2 sensor. The problem could be a leaky gasket, a failing fuel injector, or a host of other problems un-related to the O2 sensor.
Click to expand...

as i just said, it will never say 'the o2 sensor is bad.' there is no generic P-code with a definition of 'bad o2.' more than likely he has either a signal high or signal low code, which are each caused by a totally different set of problems. the only possibility that overlaps between them is a bad o2 sensor (or wiring)- but it is far from the only possible cause.

now, if the code is for the heater circuit, that points directly at the o2 (or, again, associated wiring).
 
brblx said:
as i just said, it will never say 'the o2 sensor is bad.' there is no generic P-code with a definition of 'bad o2.' more than likely he has either a signal high or signal low code, which are each caused by a totally different set of problems. the only possibility that overlaps between them is a bad o2 sensor (or wiring)- but it is far from the only possible cause.

now, if the code is for the heater circuit, that points directly at the o2 (or, again, associated wiring).
Click to expand...
this.

On the Contour forum they list 3 main causes of my P1131 code.

1. bad O2 sensor
2. vacuum leak
3. bad wiring

a forth cause seems to be random lean conditions due to fuel and additives.

all my code says is the O2 sensor detected a lean condition beyond its scope. Doesn't say the O2 sensor is dead; just excessively lean.
 
Iron woode, I live in south Texas, on the gulf.

Kornphlake, it's an OEM sensor. I didn't get it from Autozone, I had a manager friend at O'Reilly's order it for me.

I remembered the code from the first time we had it pulled (didn't find the ticket that was printed out for us) its P0130. The second time it threw the code, it was the same, plus a code for sensor 2. According to obd-codes.com, a code for sensor 2 is is P0136. I didn't get a printout of the second time it was pulled, just a quick glance at the screen before the guy cleared the code.

What's a good cable/software package to connect a laptop up to an OBDII port?
 
Raduque said:
Iron woode, I live in south Texas, on the gulf.

Kornphlake, it's an OEM sensor. I didn't get it from Autozone, I had a manager friend at O'Reilly's order it for me.

I remembered the code from the first time we had it pulled (didn't find the ticket that was printed out for us) its P0130. The second time it threw the code, it was the same, plus a code for sensor 2. According to obd-codes.com, a code for sensor 2 is is P0136. I didn't get a printout of the second time it was pulled, just a quick glance at the screen before the guy cleared the code.

What's a good cable/software package to connect a laptop up to an OBDII port?
Click to expand...
how about this?

http://www.myscantool.com/index.html
 
It's not uncommon for O2 sensors to fail if there is a problem upstream of the sensors which causes them to be contaminated. Check your PCV valve and gromet, that is what usually goes bad to give you the p1131 code, they usually get cloged or the spring in them goes bad, buy a new one and the new gromet it should cost like 5 bucks, so it isnt that expensive. That should clear up the problem, then i would replace the o2 sensor, it is probably garbage now.
 
Last edited:
Status
Not open for further replies.

TRENDING THREADS

Back
Top