P0140 code and boost gauge acting weird

**99prixgt** · 10-12-2009

I got my pacesetter headers on finally!!! 12 hr job...Anyone looking to get them, be prepared to take a walk up the "trail of tears".

Anyways I drove around, car feels way faster in the upper rpms, then i noticed my boost gauge was stuck on 20 of vacume, then the check engine light comes on shortly after and its a p0140, if im not mistaken that's a failed front 02 sensor right? does that screw up vacuum readings too? I checked all my lines and nothing is out of the ordinary, besides completely disconnecting the rear 02 for the cat but, i would think that would just give me a P0420 code, and using a 02 extension harness. Any input?

**mikedinthecity** · 10-12-2009

P0140 code (rear O2 not enough activity) as far as the boost deal seems like it would be related to the engine codee. not sure. i know you guys are scaring me from doing these mods lol.

**99prixgt** · 10-12-2009

Originally Posted by mikedinthecity

P0140 code (rear O2 not enough activity) as far as the boost deal seems like it would be related to the engine codee. not sure. i know you guys are scaring me from doing these mods lol.

Im sorry but, I have to disagree dude. P0420 is the rear 02.

**97gtsc** · 10-13-2009

Yea its the rear o2 P0140, Im getting the same thing but i have a o2 sim going bad. Id get a new o2 or sim or delete it in the pcm

**97gtsc** · 10-13-2009

Your boost prob sounds like too much back press, u still using a stock cat or aftermarket? It might be plugged? just a guess

**99prixgt** · 10-13-2009

I keep searching and I keep getting mixed codes. I thought P0420 code was the rear 02 (for the cat) and a P0140 code was the front 02 (on the manifold). Now im just plain confused...

my apologies to mikedinthecity, thank you for the input.

I have an slp catback, im also cat-less now. I could try re-connecting the rear 02 for the cat and put it in the bung and see what happens. I'm still confused as to why my boost reading was stuck on 20 vac, I would start the car, boost gauge works fine for a minute, then it's stuck on 20 vac...?

**99prixgt** · 10-13-2009

Ok I get it now...

P0420-basically a "bad cat"
P0140-02 sensor is not existent, or something along those lines

I'm going to plug back in that rear 02 and see if my boost gauge readings return to normal, I'm hoping that's the problem.

**Liquifire** · 10-13-2009

please read here:- P0140 Code Grand Prix - OBD-Codes.com

and here:OBD-II Trouble Code: P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Hope that clears things up a bit...on the first one make sure you read the last post for sure.

**BoostJunki3** · 10-13-2009

the code is because you have no cat or no 02....the vac on your boost gauge? is it newly installed??? sounds to me like its hooked up to an evap line and not a vac line....

**97gtsc** · 10-13-2009

Originally Posted by BoostJunki3

the code is because you have no cat or no 02....the vac on your boost gauge? is it newly installed??? sounds to me like its hooked up to an evap line and not a vac line....

Id check to c if there is a check-valve between the intake and the gage not allowing it to release press?

**Liquifire** · 10-13-2009

could you have over pressurized the line going to the gauge to peg it and cause it to be off on the reading? Not sure how you would, but I thought I should throw it out there...

**99prixgt** · 10-13-2009

update. I put back on the rear 02 and went for a drive, now i get a P1133 code.

Boost gauge is hooked up properly, Ive been running the boost gauge since July, when i did my top-swap...

The boost gauge reads slowly right before the ses light comes on. Then if i clear the ses light and drive the boost gauge acts normal again. Im thinking its a failed front 02 and since the pcm commands a richer air/fuel, the reading on the boost gauge gets all weird.