Question about Hyundai Motor 2002 Elantra
Both codes relate to O2 Sensor # 2
Code P0139: O2 Sensor Circuit Slow Response - Bank 1, Sensor 2
Code P0140: O2 Sensor Circuit No Activity Detected - Bank 1, Sensor 2
A faulty O2 sensor will mean incorrect signals will be sent to the EFI computer, causing erratic engine running.
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Posted on Jan 27, 2010
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From this website:
P0140 - 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.
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.
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
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
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