Question about 2003 Chevrolet TrailBlazer

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The sensor will be external and cats don't always smell like rotten eggs when they go. Also check as you will probably have a post converter sensor as well that sends a signal back to the main computer.

Posted on Oct 09, 2008


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Same Q's for 2001 Mitsubishi Eclipse GT..

Start buy replaceing the o2 sensor after the cat first o2 sensor if bad will give wrong reading i normaly tell the person lets try replaceing 2 o2 before spending 900 on a cat

Sep 28, 2015 | Mitsubishi Cars & Trucks

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2002 trailblazer I sold a 03 blazer that run good 246000 bought a 02 it ran great 117000 drove it 2000 mi it's a dog put new plugs new gas new air cleaner looked in exhaust for squirrel nest it ran great...

Wich o2 sensor did you replace? If it's the upstream one you may have a clogged Cat converter, this makes the engine run badly due to restricted exhaust flow. When you first turn the ignition to the on position make sure the "check engine " light comes on momentarily, if you notice it come on the the above is likely your problem. Scan the car for codes anyway (you still might have codes in memory!)

Best of luck!

Apr 10, 2014 | Cars & Trucks

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Mitsubishi diamante 2003, changed two o2 sensors, still hesitates at start specially when warm

there should be 4 sensors in the system two are normal O2 sensors that are located after the cat converter and two are heated sensors HO2S sensors located before the cat converter. Use the special sensor removal/installer tool so that the wires are not damaged . If you only replace d 2 sensors then you may have missed the faulty unit. The check engine light will stay on until you reset it with a scanner

Apr 05, 2014 | 2003 Mitsubishi Diamante

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How do i know if a oxygen sensor is bad verses CAM

Neither have anything to do with each other. The cam sensor is used to fire the injectors. The O2 sensors is for fuel mileage and to monitor the catalytic converter. If the O2 sensor is bad it will throw O2 codes and maybe a cat code (420). If the cat is bad, then only P0420. If the cam is bad it will set a cam code, but the ECM will go in default mode and still run the engine. Bad gas mileage, yes, But will still run. Best way to check a cat is remove the O2 sensor closest to the engine or loosen the exhaust flange. If it runs better, the cat is clogged up. Have the codes checked..

Apr 04, 2014 | 2004 Chevrolet TrailBlazer

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03 santa fe code p0421 for warm up catalyst below bank 1is it converter sensors whats bank 1 converter location compared to bank 2 is there 2 banks or converters would it be upstream or downstream if it...

If the engine is a V6 (2.7 or 3.5 lit), bank 1 is next to the firewall (right hand) when facing the back of the engine.
If the engine is a 4 cly (I4), there is only one bank and is designated Bank 1 (exhaust manifold).

The catalyst to which the code refers is the UPSTREAM, and there is only ONE upstream cat for any bank.

Clue: Two upstream O2 sensor and two downstream O2 sensors - one before the CAT and one after the CAT. the downstream O2 sensors are identical to their upstream sisters. The only reason for the DOWNstream sensor is to monitor the CAT efficiency (threshold).

The catalyst on either bank is essentially the exhaust manifold which houses the CAT... it is the only CAT to which the code P0421 applies.

Hope that helped

Feb 06, 2011 | Hyundai Santa Fe Cars & Trucks

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Check engine light is on. Code is showing P0420. What does this mean?

This code means the downstrean (behind) O2 sensor determines a reduced level of effectiveness in the cat. converter-it may not be 'lighting off' (600+ degrees) to burn any hydrocarbons left over from the combustion process. I can be that the cat is bad, or there is an exhaust leak before the cat, or the sensor itself is bad. You can do a visual inspection to determine if there is a leak, and use a scanner to see if the O2 sensor is working properly. It should read a fairly steady voltage and not switch nearly as fast as the upstream O2 sensor. The downstream O2 sensors only purpose is to monitor the cat-you might try clearing the Check Engine Light first to see if it comes back. Then you should consider contacting your dealer since you may be covered under an extended warranty that they have to put on emission devices.

Dec 24, 2010 | 2005 Dodge Grand Caravan

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Scanner says "Bank one #2

Our engines only have 2 O2 sensors. This one would be after the cat. I would replace both, but it's odd that this particular went out first. Usually it's the one upstream right next to the exhaust manifold. The O2 sensor that is after the cat is much more difficult to change due to the wire connector. It's located darn near on top of the transmission, PIA, but doable. The first sensor is the one that will give you better gas mileage, plus it's super easy to do, so replace both while you're at it. Try and stay away from Bosch if possible, both Trailblazers, and Envoys don't like these. However, I had to buy Bosch due to availability of local autoparts stores, and I'm one of the few who haven't had a problem with them.

Dec 09, 2010 | 2002 GMC Envoy

1 Answer

2003 Grand Prix service engine light on even after new catalytic

I wouldn't have gotten a cat. If the o2s are all replaced, then it could be an EGR valve

Oct 06, 2009 | 2003 Pontiac Grand Prix

1 Answer

Engine light was on and engine idles rough.

these O2 sensors are cat convertor check sensors. id be checking cat convertors and hopefully you should try replacing if not all ready is the front bank 2, O2 sensor
if you have scanner can you see fuel trims in data display to confirm high fuel trim only on bank 2 either +-5 or more indicates problem and if bank 2 sensor 2 has fixed high 700mv reading cat no good(warm idling)

Jul 10, 2009 | 1998 Isuzu Rodeo

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2001 Nissan Maxima service engine light stays on code from Auto Zone scanner is PO139 and PO138. What should my next step be to solve this problem.

code p 0138 refers to 2 items
1--heated oxygen sensor(HO2S) 2 bank 1--high voltage ==causes --wiring short to positive --HO2S---ECM
2--oxygen sensor (O2S) 2 bank 1--high voltage ===causes wiring short to positive ---ECM
code p 0139 refers to 2 items
1--- heated oxygen sensor (HO2S) 2 bank 1--slow response ===causes --heating inoperative --wiring--ECM
2--oxygen sensor (o2S) 2 bank 1 slow response ===causes --wiring --- O2S

heated oxygen sensors9HO2S) are in the exhaust manifold before the cat converter
Oxygen sensors (O2S) are after the cat converter
it is indicated that the HO2S is faulty-
check the wiring and /or replace both sensors

Nov 16, 2017 | 2001 Nissan Maxima

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