O2 sensor and P0140

[Zack Conner]

Hey Eric, first I’d like to say hello. I’m having a problem with my o2 sensor. I just replace it two days ago and the check engine light is already back on. What other symptoms can cause an O2 sensor to cause the check engine light with this code to come on so soon? I have a 200 Dodge Neon.

Topic

[Ingvar]

[i]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.

Read more at: http://www.obd-codes.com/p0140
Copyright © OBD-Codes.com[/i]

[dan]

this code is primarily for the upstream 02 sensor, this sensor is responsible for telling the PCM how rich or lean the engine is running buy measuring oxygen in the exhaust. the richer the air fuel mixture the less oxygen the higher the voltage, the leaner the air fuel mixture the lower the voltage…

your code can be caused buy several things, falty 02 sensor, falty wiring and bad connections too 02 sensor, or a lean or rich condition.

the first thing i would suggest, check the wiring and the connections too the o2 sensor, make sure they aren’t broken, if they aren’t if you can get a scan tool that reads live data read voltages for B1S1 bank one sensor one, this should be between .300-.800 give or take a little, if you can tell us what you are seeing on the scantool as far as voltage readings for the upstream O2 sensor that can help us narrow it down, best too observe these things with PCM in closed loop this usually happens when engine has reached operational temperature.

[college man]

see if this helps.

[Author]

Replies