Appreciate any thoughts/solution/advice.

Issue: Throwing P0138 CEL/SES error (Rear O2 Sensor High Voltage)

Background: Error occured when running car after install of cams and ported parts (manifold/o2 housing/hotside).

Additional Notes:

• Running catless with Helix test pipe w/ Oxygen bung
• No CEL/SES for over a year+
• Running standard bolt-ons, etc. in addition to above mentioned mods
• Code only appears after running car, driving around, then starting up car second time

Troubleshooting:

1. Checked O2 sensor wiring, all secured
2. O2 sensor appears to be intact
3. Checked voltages on O2 sensor
4. Front sensor runs voltage oscillating anywhere between 0.800 and 0.100
5. Rear sensor runs voltage steady between 0.680 and 0.700

Questions:

• Is the O2 sensor bad?
• Wouldn't a bad O2 sensor run NO voltage at all?
• Should the rear sensor oscillate voltage similar to the front? Or it hold a specific voltage value?
• Is it possible that the additional flow from porting and cams would throw off the rear O2 sensor readings enough to throw the CEL/SES despite the oxygen bung?
• Should I try another anti-fouler?
• Should I try the mechanical O2 simulator resistor mod?
• How valid is the theory because the oxygen bung off the test pipe is beneath the pipe that condensation has accumulated and destroyed the O2 sensor itself?

 

Contact Ultimate Racing and see if Johnson can help you.

 

Last time I contacted them, they weren't very insightful....

Bump.

 

What was your fix?

 

None found yet.
Still running an intermittent CEL, carry around a OBD reader just in case.

Planning on swapping in a good rear O2 sensor soon to validate that the sensor is bad.

 

any luck with swapping out the rear o2? i had the same code come up today. i tried a new sensor in the o2 housing with no luck. my cars rpms will drop to below 400 rpms then back up to normal whenever i depress the cluth while driving at the same time it throws the code. im gonna try replacing the rear o2 next. good luck with yours.

 

are you running a test pipe?? if so you might wanna invest in a cel fix

 

I have the issue, totally stock. I'm going to bring it to the dealer soon, as it's still under warranty....has any one done this, does it need to be replaced?

 

Any luck fixing the problem?

 

This thread is over a year and a half old.
he fixed the issue by replacing the rear 02 sensor with a non-OEM one, i think.

 

^^ I would think replacing it would fix it. I doubt the sensor being OEM or not makes a difference.

 

Yeah, I know this thread is old.


Have the same issue all of a sudden.

Bought new O2 sensor and the code was gone. Yesterday my car hesitated to start a bit( below zero temps and mini battery), and when it finally cranked over, I had the p0138 code again.


Weird thing is, it only throws the CEL seconds after I start the car. Not while it's running. At $160 a pop, i'm hoping I don't need another O2.

Any answers?

 

I have the same issue. I'm just going to entirely remove the downstream o2 as it only is there to let you know if your cat is working properly. I'm replacing it with the Perrin o2 simulator. No more codes from that o2.

 

So, you are currently running the Perrin o2 simulator /out any issues?

Crazy thing is, I have been running this mechanical fix for over a year now, w/ zero issues. All of a sudden with the snow, I'm getting the P0138 code. I even wrapped the new O2 sensor to prevent moisture from getting in there.




I'm trying to sell my car, and can't/ don't want to sell it w/ a SES light. TIA.

 

Any one?