My car started running a little bit rougher than usual about a week ago and today my check engine light went on. I pulled the code and got codes 25 and
According to the manual one is for an overly rich air/fuel ratio and one is for a overly lean air/fuel ratio. Sounds weird to me, but I checked 3 times. First it brings up 25 and then 26. Where do I go from here?
The car has 180K/mi on it and the spark plugs were changed about 45K ago. If you guys need any more info please let me know. Thanks so much.
The ECU will always store diagnostic trouble codes (DTC) from lowest numerically to highest numerically.
Since the 2 codes you listed are opposite in nature, I would start by checking the things that have an effect and measure air/fuel ratio.
First, the stuff that will have an effect on air/fuel ratio:
Check the condition of the black plastic tubing that runs from the air filter housing to the throttle body for cracks, holes, or gaps.
Check the air filter to make sure it is not clogged, torn, or warped.
Check for any manifold vacuum leaks or disconnected vacuum hoses, paying attention to vacuum switching valves to make sure they are not cracked or damaged.
Check the mass air flow sensor to make sure the connector is secure. There is a wire inside the MAF sensor that heats up, and is cooled by air passing through. If the wire is dirty, it won't sense properly. You can try cleaning it by giving it a shot of carburetor cleaner and letting the liquid drip out of the opening. Do not damage the wire, or you will need a new MAF sensor. My guess is that a dirty or clogged MAF sensor is the cause.
If you use a lot of cheap gas, try a bottle of Chevron Techron fuel injector cleaner and see if that helps.
If you used anything other than OEM spark plugs and related ignition parts when you replaced them, stick to OEM the next time you replace them. Some aftermarket ignition parts don't last as long as OEM. Check the condition of the spark plugs to see if they have a uniform, fine-gray color.
Next, check the stuff that measures the air/fuel ratio, which is basically the O2 sensor. Use your shop manual and a multimeter to check the O2 sensor and while you're at it, check to make sure the connector is not damaged or loose. If the O2 sensor does not check out according to the manual, replace it with an OEM O2 sensor.
Thank Ray...I also have a little more information.
I just changed the air filter today after getting the trouble codes hoping that would be a simple fix. I also pulled the plugs and they look good like I'm burning clean. As I recall, the codes should clear themselves when I restart the car if the problem/s were fixed. Sadly they are still there. Also, I'm not positive, but I think I have been using more gas than usual.
OK, you can rule out the air filter and ignition system.
The codes on the first generation on board diagnostics (OBD I) will not clear themselves. Pull the ECU main fuse or disconnect the negative battery terminal for about 5 ~ 10 seconds to clear the codes.
If you are using more gas, try the Chevron Techron and check the MAF sensor.
As Ray mentioned, yours does not self clear.. But even if it was OBD-2, it often will take a while for this to happen, the amount of time depending on the circuit in question. It will almost never be instantly off the next time you start the car. It will have to run it's various tests, and when they quit failing, then it will eventually kill the light. This can take a few run cycles in some cases. MK
In a vehicle with OBD II, the system needs to see 2 drive cycles without detecting the fault to extinguish the check engine light. A "drive cycle" is a cold start, driving at X MPH for a certain distance, then driving at Y MPH for a certain distance, with engine coolant temp reaching normal, the ECU reaching closed loop operation, and the transmission running through all of the gears and lockup.
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