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Trouble Code P0140

08-21-2010, 12:09 PM
I have a 2002 Grand Am with a 3.4. I replaced both O2 sensors, the catalytic convertor and nothing. I bought an O2 simulator and plugged it into the rear and reset the computer. I was good for about 2 weeks and now same light, same code. I'm guessing something maybe wrong with the computer... Where is the computer located on these cars?

08-21-2010, 01:21 PM
I think I would look at the data for the rear O2 sensor with a scan tool and with a good voltmeter at the sensor. Id there is no data on the scan tool but data on the volt meter than there is a bad wire/connection somewhere.

08-21-2010, 07:30 PM
First, check fuse #47 (Canister Vent Valve, Exhaust Oxygen Sensors) in the hood fusebox.

I would also look at the PCM side, the connection could be oxidated.

Obiviously, check for wire damage.


P0140 - 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

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.

09-19-2010, 11:40 AM
Fuse #47 is fine. Can anyone tell me where the pcm is located on this car? Is it in the passenger side kick panel?

09-19-2010, 04:06 PM
The PCM is under left side of instrument pannel, near the steering column.

I'ld check for the wires condition and connector pins for oxydation.

Pinout for the Heated O2 sensors:

Sensor 2: Cat. out
Brown: 12V in run position, from fuse 47
Black: ground
Tan/white: PCM pin 28: H2OS 2 low
Purple/white: PCM pin 11: HO2 sensor 2

Sensor 1: Right exaust manifold
Brown: 12V in run position, from fuse 47
Tan: intake air temperature sensor (at left of engine)
Purple: PCM pin 10: HO2 sensor 1 (heated o2 sensor)

Tan: to O2 sensor 1
Black: to PCM pin 12: Sensors ground

10-03-2010, 01:10 PM
Update: When the muffler shop installed the cat last year they didn't weld the pipe all the way. I found a 1/4 gap on the top of the pipe before the cat. I'm almost certain that was the cause of the P0140 code. Thanks for all your guy's help.

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