SES Light still on...suggestions?

[99 GTP]

replaced both front and back O2 sensors and SES light came back on.....any suggestions, I reran the codes and keeps coming back second sensor. 99 GTP

[BNaylor]

Originally Posted by 99 GTP

replaced both front and back O2 sensors and SES light came back on.....any suggestions, I reran the codes and keeps coming back second sensor. 99 GTP

How many miles on your GTP? And is the CAT convertor the original? If you're getting a P0420 DTC error code its the rear 02 sensor picking up CAT convertor inefficiency.




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[99 GTP]

99 GTP w/ 110k miles on it. The CAT converter is original on the car. It's been a great car, just started running into some minor problems. Thanks for the reply, what kind of cost will I run into replacing the CAT??

[BNaylor]

Originally Posted by 99 GTP

99 GTP w/ 110k miles on it. The CAT converter is original on the car. It's been a great car, just started running into some minor problems. Thanks for the reply, what kind of cost will I run into replacing the CAT??

CATs vary in cost. A good hi-flow can run around $100 to $250 not counting labor to install. The stock GM CAT runs around $200.

If you're not interesting in any performance gain, a universal CAT with installation runs around $100.00.

I'd go with a hi-flow CAT. It makes a difference and do a u-bend delete if you already have not done so.




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[richtazz]

did you clear the codes with a scanner after replacing the sensors? The computer won't recognize the new sensors if you didn't.

[99 GTP]

Original problem, SES light came on, ran code, front sensor, replaced, reset codes. SES light on again, rear sensor, replaced, reset codes. SES light on AGAIN, codes come back rear sensor, check function of rear sensor, works fine, SES light still on.

Just checked pricing for aftermarket CAT $181, GM part $442

[BNaylor]

Originally Posted by 99 GTP

Original problem, SES light came on, ran code, front sensor, replaced, reset codes. SES light on again, rear sensor, replaced, reset codes. SES light on AGAIN, codes come back rear sensor, check function of rear sensor, works fine, SES light still on.

Just checked pricing for aftermarket CAT $181, GM part $442

$442 is GM's list retail price. GMPARTSDIRECT.COM $310.00. The reason why the GM one is so expensive is because it comes complete with the header/downpipe and flanges where it will be a bolt on operation.

Either way go for a new CAT and then you can put that scanner/code reader away for a while. Good luck!



Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[richtazz]

If the light was reset and it came back I agree with bnaylor, the cat needs replacing.

[99 GTP]

Thanks guys, you have been a huge help, I will have the CAT replaced. Great resource for GP's, I'm sure to be back at ya!!!!

[99 GTP]

OK, replaced the CAT. This isn't the good part, SES light back on after the second time I started the car. Code PO140...... what the heck!!!! Need help if possible, I didn't look up that code yet?????

[BNaylor]

Originally Posted by 99 GTP

OK, replaced the CAT. This isn't the good part, SES light back on after the second time I started the car. Code PO140...... what the heck!!!! Need help if possible, I didn't look up that code yet?????

P0140 is "O2 sensor CKT no activity, bank 1, sensor 2". CKT means circuit. Check or re-seat the electrical connector to the rear O2 sensor and make sure its pushed in correctly.

Out of curiousity what brand O2 sensors did you install. Were they the OEM AC Delco or Bosch type?




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[99 GTP]

I used the AC Delco sensors. I'm going to recheck the connection, I don't think I'm doing it wrong but you never know. The car is also sputtering going up a hill, will this be due to the SES light and sensors not functioning (connected) properly??? By sputtering I mean trying to down shift then bouncing all around like it can't make up it's mind.

Thanks......

[BNaylor]

Originally Posted by 99 GTP

I used the AC Delco sensors. I'm going to recheck the connection, I don't think I'm doing it wrong but you never know. The car is also sputtering going up a hill, will this be due to the SES light and sensors not functioning (connected) properly??? By sputtering I mean trying to down shift then bouncing all around like it can't make up it's mind.

Thanks......

What was the original odb-ii DTC error code before you changed the 02 sensors?

Have you tried doing a total reset of the ECU/PCM and forcing it into re-learn mode? Also check the EGR valve. You can remove to see if carboned up. Also make sure the spring loaded rod moves freely.





Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[99 GTP]

Thanks, for the reply. I'm sorry I didn't write down the original error code, I've been having several problems over the last few months.

I'm going to take your advice and do the step mentioned and get back with you. I can't get to it right now but I will update.

Thanks......

[99 GTP]

Reset the connection, seems to be the fix. I'm not perfect around a car, but I'm learning as I go.

I going to test drive this afternoon, any other suggestions are welcome. Oh, and I checked the EGR valve, didn't notice anything out the ordinary.