4 Trouble codes/TCS and RPM issue.

**aeidian** · 05-16-2010

1999 GTP 3800 V6

Took the car to an O'rielly Auto Parts and read the codes with their device and had the following pop up:

Catalyst System Efficiency Below Threshold (Bank 1)
Research shows the code P0420

Evaporative Emission Control System Pressure Sensor High Input
Research shows the code is P0450

Exhaust Gas Recirculation Error (EGR Number 2)
Research shows the code is (possibly) P1404

Symptoms:

Sometimes the vehicle turns over but does not start, usually turning the key off and on a few times the car will start up roughly then idle out regular.

Resonator has a busted out hole on the top, patched it for the time being with a muffler sheet metal kit.

Seems to be some kind of liquid, like water, near where the down pipe bolts to the manifolds that smokes. Only noticed this once.

While driving the car sometimes chokes and dies. Happens at random times, but often just cruising at 50-60, not revving up or down.

While driving the car seems to "skip" once and then the RPM gauge drops to zero, TCS off light comes on and stays on. Car continues to run fine just no RPM read and the TCS light stays on even if you press the button. Restarting the vehicle seems to correct.

Actions so far:

Patched resonator.

Used Seafoam, adding half a can to a half a tank of gas, half a can to the intake via the brake booster vacuum hose.

Based on the above information (and/or information provided if questions are asked below), please suggest what might be causing the above trouble codes and RPM/TCS issue. Thanks.

**Bio248** · 05-17-2010

first thing you need is a new o2 sensor.

**aeidian** · 05-17-2010

Originally Posted by Bio248

first thing you need is a new o2 sensor.

I suspected it might be the downstream o2 sensor, the one right after the catalytic converter, but wanted some confirmation before I spent the 70 bucks to replace it. Based on the information, do you think the o2 sensor just went bad, or something caused it to burn out? Meaning if I buy a new one and put it on, what's the likely hood it'll just burn out too?

**Juanmiguel** · 05-17-2010

Originally Posted by aeidian

1999 GTP 3800 V6

While driving the car seems to "skip" once and then the RPM gauge drops to zero, TCS off light comes on and stays on. Car continues to run fine just no RPM read and the TCS light stays on even if you press the button. Restarting the vehicle seems to correct.

That's gonna be the crankshaft position sensor. Mine had it when I bought it.

**aeidian** · 05-17-2010

Originally Posted by Juanmiguel

That's gonna be the crankshaft position sensor. Mine had it when I bought it.

Your vehicle had this same issue? Replacement of the CPS fixed the issue?

**00RegalGS** · 05-17-2010

The stalling and the tac not working is most likely the crank sensor like juanmiguel said. As for the o2 sensor, depending on the mileage of the car the cat could also just be going. i'd get it monitored first so you dont waste your money on an o2 sensor and it ends up being the cat.

**aeidian** · 05-17-2010

Originally Posted by 00RegalGS

The stalling and the tac not working is most likely the crank sensor like juanmiguel said. As for the o2 sensor, depending on the mileage of the car the cat could also just be going. i'd get it monitored first so you dont waste your money on an o2 sensor and it ends up being the cat.

144K on the vehicle, everything stock. Please explain how I would get the cat monitored.

Originally Posted by TorqueAutoMotiv

the O2 sensor is the most over replaced item in the emmissions related items and its the most over looked as standard maintnance
Its easy to test it though put a micrometer Or scaner on the car and see if the volts jump up and down in relation to gas

the tach issue sounds like the crk sensor as stated

and if the rear o2 sensor is reading high to low voltage probably means your cat is in need of replacement

Am I able to check the voltage with a scanner tool like I used to find the codes? If the voltage jumps up and down then it's the cat, what reading could I expect if the o2 sensor is bad, would it just not show any voltage?

**rmcardle3** · 08-21-2010

I was just looking at this on Alldata DIY and it said both HO2S (1 and 2) are capable of swinging voltage in the range of 100mV-900mV. The front HO2S 1 should be a swinger. The back HO2S 2 is not a swinger. It says if the back HO2S 2 is:

STEADY ~450mV, then the P0420 issue should disappear and there should now be no SES light.

SWINGING between 100mV-900mV and the HO2S 2 is doing its job and is reporting that the problem is UPSTREAM of the HO2S 2.

If I understand these right, changes in the HO2S 2 voltage over time is the key of, even knowing were to begin. Please join in if I overlooked something, hope this helps. I will post details as they become available.
===============================

Which brings me, to MY PROBLEM?

I NEED/WANT a Scanner/Programmer:

I need a scanner so I can perform this test. I want a programmer as an option /stepping stone to resolving this issue and having a programmed/copied version of my stock setup minus the one DTC, (deleted P0420) on a "custom" pcm for my 2000 GTP.

I need to pick a scanner, but want a programmer. I just don't have $250,00 for a new programmer, now (if I could even, find one). I have looked EVERYWHERE I can think of using every search tag I can think of, DHP, HP Tuner,................

Sorry if I put to much emphysis on the "I need a PCM programmer for my 2000 GTP". This may be another subject for another thread.

**jgbigguy** · 08-24-2010

Any definitive catches on this? I just bought my 98 GTP and i took it to the mechanic for a safety inspection. He told me that the person i bought it from put in a straight pipe which had removed the CAT. This was of course causing the cat efficiency code and my SES light. He had also said that it was throwing the misfire code complete with the flashing SES. It only flashes when i really jump on it. The mechanic and my brother, an ex mechanic, says that since the rear O2 sensor is either out of the exhaust, or getting readings with no cat, it is trying to lean out my gas when i jump on the throttle. This leaning out of the gas is what is causing the misfire in the engine. I still plan on doing a tune up on the vehicle with new plugs and wires and testing to make sure the coils are good. When i get on it it sounds like there is a fluttering air sound coming from the engine...the car continues accelerating but has moments of much harder acceleration...like i said i just bought the car and have still yet to dive into the engine and check it all out. So far its the only vehicle between the wife and myself so i dont want to start tearing things apart if i can't run up to the auto parts store if i break something...Im new to this whole tuning building thing so any and all help is welcome. Thanks

**CTKGP09** · 05-17-2010

CPS or MAF would be the cause of the running problem

**TorqueAutoMotiv** · 05-17-2010

the O2 sensor is the most over replaced item in the emmissions related items and its the most over looked as standard maintnance
Its easy to test it though put a micrometer Or scaner on the car and see if the volts jump up and down in relation to gas

the tach issue sounds like the crk sensor as stated

and if the rear o2 sensor is reading high to low voltage probably means your cat is in need of replacement

**Bio248** · 05-17-2010

the P0420 is the downstream one after the cat. if you replace it and it's still coming on then your cat is now going out and then honeycomb in it is degrading and going through your exhaust.