O2 Sensor malfunction is causing my Check Engine light to come on

[dasander]

Hi, my name is Dan Sanders and this is my first post on DSM forums. I bought a 1995 Eagle Talon Tsi AWD and the check engine light has been on ever since, even though the car seems to run relatively well. I got the codes read at a Dodge dealership and the error messages that came from my engine light are as follows:
1. Fuel Trim Malfunction
2. O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
3. O2 Sensor Heater Circuit Malfunction(Bank 1 Sensor 2)
4. Insufficient Coolant Temp. for closed loop fuel control.
The mechanics at the dealership suspected these errors had to do with my aftermarket exhaust and the O2 sensor. I bought the car with the aftermarket exhaust already installed and I later added a 3" downpipe to the system. Those of you who have installed aftermarket exhausts, do you have any idea what could cause this problem or do you suggest just to buy a new O2 sensor? Also when my car is in idle when stopped, the RPMs seem to fluctuate higher than normal at around 2500 RPMs. I suspect that the error I have with the O2 sensor is related to this problem as well. If any of you guys could help me out, it would be much appreciated. Thanks.

 

[Grimis]

2. O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

3. O2 Sensor Heater Circuit Malfunction(Bank 1 Sensor 2)

Thats the rear o2 sensor, Have you checked the plug/wires under the driver side seat? Under the car as well? More then likley its your rear o2 sensor is shot, I have the same problem, rear o2 is shot

4. Insufficient Coolant Temp. for closed loop fuel control.

Check your Coolant Temp sensor, and your front o2 sensor.


As for you first one, Someone will chime in for ya. Good luck and Welcome to the world of DSM on Dsm Tuners

 

[ADrewzki]

Replace your plugs and make sure they are properly gapped. While you're at it, replace your wires also. Bank 1, sensor 2 indicates rear O2 sensor. It could be that your O2 sensor is either not working or disconnected or you run a catless exhaust system. Get your temp sensor checked. Is your engine overheating or anything? Welcome to the world of DSMs.

 

[ddavisaf]

First step would be to never take it to the dealership to get codes ran. Autozone or Checkers or places like that will run your codes for free where as the dealership usually charges you. When you replace the o2 sensor and the coolant temp sensor reset your ECU by disconnecting the battery for a good two minutes. Drive it around for a while and if your CEL comes on again we'll go from there. A lot of times codes are thrown because of o2 sensors, and once that is fixed they're gone.

 

[halligoo]

A lot of times codes are thrown because of o2 sensors, and once that is fixed they're gone.

Absolutely. I replaced my front 02 sensor and cleared 4 codes. I think the heater circuit is in the front sensor, not the rear. If you have the $$$ just replace both sensors and go from there.

 

[akdsmer]

Dan,

When you have multiple codes, start with the code that will affect the rest. In your case, it looks like two problems

1) Rear O2 sensor heater problem. If the heater is inop, then the sensor does not come up to temperature and the computer sees this. I don't have a OBDII DSM, but usually the voltage will be 0 or very close to it until the heater comes on line (gets hot) If it PCM does not see this, then it may set the second code for O2 sensor circuit malfunction. Check power and grounds to your heater circuit. They are usually the two wires that are the same color. (a 2G owner can verify this for you) If power and grounds are good then ohm check the heater circuit. If it's open, replace the sensor. The rear O2 sensor has very minimal fuel control functions on any OBDII vehicle, so the fuel trim malfunction should not be a result of the rear O2.

2) Verify the coolant temp sensor operation compared to actual engine temperature. If the engine is hot (195 degrees), then the CTS (coolant temp sensor) will provide very little resistance to the circuit and drop the 5V reference to the sensor to around .5V. You can check this with a meter...simply unplug the CTS check which wire has 5V and then reconnect, stick a t-pin (or paperclip) into the backside of the connector next to the wire. Place you meter on that wire and read the voltage. Remember, if your engine is not hot the reading will be a higher voltage. Let me know what you find. Don't chase the Fuel trim malfunction until you have the first obvious problems (CTS and Rear O2) fixed first. A scan tool is the easiest way to check the CTS and actual O2 sensor voltage output (but NOT the heater circuit) so if you can borrow one, that would be a great start!

You could also say what the heck and just throw a couple parts on your car also!