Check engine code: where should I start?

[jlatenight]

Hey guys, Check engine light came on the other day, got the codes checked and they came back as: P0442 -Evaporative Emission Control System Leak Detected (small leak)
P2272 -O2 Sensor Signal Stuck Lean Bank 2 Sensor 2
My Tahoe has 108k miles on it, so maybe there's a corrosion leak in the EVAP system somewhere? Can anyone guide me on where I should start with this? Around O2 sensor Bank 2 Sensor 2? Where's what? Thanks in advance for your help!! -Jon

 

[Erik G]

Bank 2 Sensor 2 is passenger side after the Cat. I did one on my Sierra, got the part at Orilies cheap, perfect fit.

 

[jlatenight]

Thanks Erik, So you think, given those two codes, I should just replace the sensor and see if the codes go away?

 

[Erik G]

The evap code is more likely your gas cap. I've never had a false code on the oxy sensor though. How does it run and sound? usually the bad oxy sensor will result in pulled timing, not as much get up and go, and bad MPG

 

[Erik G]

the sensor code could be:

Exhaust Leak near O2 Sensor
Contaminated or Failed HO2S2 (Sensor 2)
HO2S2 Wiring/Circuit Problem
Loose installation of HO2S2
Fuel Pressure Incorrect
Faulty Fuel Injector
Engine Coolant Leak
Faulty Purge Solenoid Valve
PCM has failed

on my sierra, what actually happened was the dual exhaust hanger broke, my exhaust hung down a bit and was loose. I think it just yanked the wires around too much. Replaced it, and the truck started running much better and all the power was back

 

[jlatenight]

It seems to idle *slightly* rougher, but not much. Power seems about the same, maybe a little less now that you mention it, but nothing major. I took a quick look underneath around the bank-2 sensor-2 area and didn't see anything obviously out of wack. I tightened the gas cap too, but it didn't seem loose. I guess I'll just order a new sensor, throw it in and see if the check engine light clears.

 

[jlatenight]

So bank-2 sensor-2 is the sensor right after the cat on the passenger side, right? Is that position considered "downstream" then? I'm looking at these two and they have different connectors
Denso 234-4668 (upstream) http://amzn.com/B00199BXU2
Denso 234-4256 (downstream) http://amzn.com/B003YNF9CO

Without actually checking the connector (at work), is there a way to confirm the OEM part number for bank-2 sensor-2?

 

[Erik G]

Downstream

Basically, with 2 cats and 4 sensors, Upstream is before the cat, downstream is for after the cat. What these sensors are doing is measuring that the cat is working

I don't know the year of your truck, but I come up with the same 234-4256 part number for my 2011 5.3 SLT Yukon

 

[Erik G]

on the check engine lights and re-setting, I'm not sure how our trucks work. the previous Sierra I had was an 04, I had to clear the codes with my code reader, and then do a full drive cycle to verify that they didn't come back on.

a drive cycle for GM is the following (and please be careful, I would always do it early on a sunday morning with the freeway empty)

To perform an OBDII Driving cycle do the following:

1. Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
2. Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
3. Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
4. Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
5. Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
6. Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.
7. Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
8. Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.