Help diagnosis my CEL

[Willywongka]

Hey guys i was driving my car the other night and 3 cels popped up. P0100, p0110, and p0140. I did a little research and it seems the problems may be in the maf or the o2 sensor. So i took off the maf and cleaned it with maf cleaner and i unplugged the harness to the o2 sensor and connected everything back up.

I know it takes a little bit of driving before the ecu concludes that the problems are fixed before the cels turn off. So far i have driven about 30 or so miles and the cel is still lit. Do i need to drive more before i can conclude that cleaning the maf didnt solve the problem? I have a spare maf i can throw on, but i wanted to drive a little bit longer before i do that.

Honestly, my car sees to drive just fine even before i cleaned the maf. Just thought i would ask you guys to see if you guys could give me a little assistance, thanks.

-will

[mx54life]

Do a diagnostic scan. I would guess O2 sensor or CAT prob. It takes a series of slow and highway speed to do a cycle.
If you are nearby I have an OBD2 scanner. I think you can also borrow them from Autozone.

[Willywongka]

Yeah, i have a obd2 scanner. Thats how i pull the codes, just wondering if you guys may have experienced these cels as well. Hmmm thanks for the help!

[mx54life]

I do most of the time but I clear the codes with my scan gauge.

[Willywongka]

I didn't want to clear the codes cause I didn't want to go through the trouble of doing the annoying drive cycles again.

[kung fu jesus]

Clear the codes. They are still there

[90blue]

This from the web
MX54life is correct

OBD-II Trouble Code Technical Description

02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

What does that mean?

The Powertrain control module (PCM) will provide a .45 volt reference voltage to the Oxygen sensor. When the O2 sensor reaches operating temperature, it will generate a voltage that will vary depending on the oxygen content of the exhaust. Lean exhaust generates a low voltage (less than .45V) and rich exhaust generates a high voltage (greater than .45V).

O2 sensors on a specific bank marked as "sensor 2" (as this one is) are used to monitor emissions. A Three-Way Catalyst (TWC) system (catalytic converter) is used to control tailpipe emissions. The PCM uses the signal received from Oxygen sensor 2 (#2 indicates aft of catalytic converter, #1 indicates pre-converter) to read efficiency of TWC. Normally this sensor will switch between high and low voltage at a noticeably slower rate than the front sensor. This is normal. If the signal received from rear (#2) O2 sensor indicates that the voltage has "stuck" between .425V to .474 V, the PCM determines this sensor is inactive and this code will set.

Potential Symptoms

Your check engine light(CEL), or malfuction indicator lamp (MIL) will be illuminated. There will not likely be any noticeable drivability problems other than the MIL. The reason is this: The rear or post catalytic converter Oxygen sensor does not affect fuel deliver(this is an exception on Chryslers). It only MONITORS the efficiency of the catalytic converter. For this reason, you will likely not notice any engine trouble.

Causes

The causes for a P0140 code are fairly few. They could be any of the following:
•Shorted heater circuit in O2 sensor. (Usually requires replacement of heater circuit fuse in fuse block also)
• Shorted signal circuit in O2 sensor
• Melting of harness connector or wiring due to contact with exhaust system
• Water intrusion in harness connector or PCM connector
• Bad PCM

Possible Solutions

This is a fairly specific problem and shouldn't be too difficult to diagnose.

First, start engine and warm up. Using a scan tool, watch the Bank 1, sensor 2, o2 sensor voltage. Normally the voltage should switch slowly above and below .45 volts. If it does, the problem is likely intermittent. You'll have to wait for the problem to surface before you can accurately diagnose.

However, if it doesn't switch, or is stuck then perform the following: 2. Shut off vehicle. Visually check the Bank1,2 harness connector for melting or chafing of the harness or the connector. Repair or replace as needed 3. Turn ignition on, but engine off. Disconnect the O2 sensor connector and check for 12Volts at the Heater Circuit supply and for proper ground on the heater circuit ground circuit. a. If 12V heater supply is missing, check the proper fuses for an open in the circuit. If heater circuit fuse is blown, then suspect a bad heater in the o2 sensor causing a blown heater circuit fuse. Replace sensor and fuse and recheck. b. If ground is missing, trace the circuit and clean or repair ground circuit. 4. Next, with connector still unplugged, check for 5 Volts on the reference circuit. If this is missing, check for 5 Volts at the PCM connector. If 5 Volts is present at the PCM connector but not at the o2 sensor harness connector, then there is an open or short in the reference wire supply between the PCM and the o2 sensor connector. However, if there is no 5 Volts present at the PCM connector, the PCM is likely at fault due to internal short. Replace PCM. ** (NOTE: on Chrysler models, a common problem is the 5Volt reference circuit can be shorted out by any sensor on the car that uses a 5 Volt reference. Simply unplug each sensor one at a time until the 5 Volts reappears. The last sensor you unplugged is the shorted sensor. Replacing it should fix the 5 Volt reference short.) 5. If all the voltages and grounds are present, then replace the Bank 1,2 O2 sensor and re-test.

[Willywongka]

I guess I have no choice but to clear the codes. Would the O2 sensor before or after the cat be the culprit? Thanks for the input guys!

I would like to note that I think my aftermarket magnaflow cat is probably on its way out, dunno if that could be part of the problem.

[BoBo]

BTW, when it comes to cats always buy OEM 3 way, aftermarket cats never lasts.

[mx54life]

How many CAT does your car have? If the cat is bad the sensor will not be able to send the proper data thus the code comes. If you change the sensor and the code still appears then it is the cat. The upstream O2 sensor seems to go first from what I have gathered.
Are you due for a smog?

[kung fu jesus]

OK, I'm on a computer now, can see your car and year. Generally, with that many codes related to emissions, I would strongly suggest looking at the strength of your ignition. You could diagnose the root of each of the codes, replace the O2, cat, but if your ignition is getting weak, you will have the same issues soon in the future. It's just simple diagnostics with a mutitester. For instance, when I lived in CA, I had a 10ae with CA emissions. The front cat went bad, replaced it at great expense, passed but the cat became fouled within 20k miles. Same codes came back. I tested the coils and ignition and found it was getting weak...not really getting good combustion, fouling the cat and O2s.

I'm not saying this is your fix, but I would be suspicious of shotgunning the emissions sensors and cat(s) as a long term solution. Good luck!

[Willywongka]

How many CAT does your car have? If the cat is bad the sensor will not be able to send the proper data thus the code comes. If you change the sensor and the code still appears then it is the cat. The upstream O2 sensor seems to go first from what I have gathered.
Are you due for a smog?

I have a 96 Miata so I only have one cat thankfully! The cat is a Magnaflow and has been on my car for a few years now so it's probably dead. I don't have a smog coming up so I'm not worried about getting it fixed right away, it just annoys me when my car isn't running well =/.


OK, I'm on a computer now, can see your car and year. Generally, with that many codes related to emissions, I would strongly suggest looking at the strength of your ignition. You could diagnose the root of each of the codes, replace the O2, cat, but if your ignition is getting weak, you will have the same issues soon in the future. It's just simple diagnostics with a mutitester. For instance, when I lived in CA, I had a 10ae with CA emissions. The front cat went bad, replaced it at great expense, passed but the cat became fouled within 20k miles. Same codes came back. I tested the coils and ignition and found it was getting weak...not really getting good combustion, fouling the cat and O2s.

I'm not saying this is your fix, but I would be suspicious of shotgunning the emissions sensors and cat(s) as a long term solution. Good luck!

So if I have a weak ignition, does it pertain to the coilpack that would be causing that? Thanks for the tips, definitely gives me more to look at as opposed to just replacing parts.

[kung fu jesus]

Generally, yes. A lot of people might just throw spark plugs and wires at it, but the coils' health is often overlooked.

[mx54life]

Straigth test pipe and reserve the b/n cat for smog.

KFJ is right coils could be the culprit too. They are inexpense are they not?