Sensor/catalyst problem? Hy guys, i hope someone can help me out with my problem. I have a Malibu 1998. When i start my car the engine starts to work onregular,so not on tune,it's idle high and then low, so up and down. Then after 15 minutes it's starts pushing out the exausta a very bad smell and finally after aprox. 45 minutes it's just turn out. Then i try to start it again but it won't start without giving it some gas. I have to wait till the engine cools off to start it again. Thank you very much, hoping you can give me some advise, Egbert Kock Oranjestad,Aruba Dutch Antilles

First let's see what's missing, fuel, spark or both. Do this remove a plug wire or coil on plug the insert a screwdriver into the boot and then hold the metal part of the screwdriver 1/2in. from a metal part of the engine block then have someone crank the engine while you watch for spark. Check fuel, do this remove the cap from the fuel rail test port and depress the schraeder valve while someone turns the switch on, fuel should spray out. NOTE to avoid fire do these tests in this order. I wonder about your fuel pump. I hope this helps. Take care.

I don't show anything special in the wiring diagram. The power goes from the key switch, thru the neutral safety switch on the transmission, to the starter. I guess the switch on the trans could be unplugged fairly easily.
Obviously you would check for any missing fuses and relays in the box in the engine compartment and under the dash.

Hi there:

DTC P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
A vehicles' catalytic converter (catalyst) helps improve tailpipe emissions by oxygenating the exhaust gasses. It helps convert hydrocarbons (HC), Carbon Monoxide (CO), and oxides of Nitrogen (NOx) into water vapor (H20), Carbon Dioxide (CO2), and Nitrogen (N).



The PCM (Powertrain control module) monitors the catalyst efficiency by means of a post-catalyst Oxygen sensor. This sensor is used primarily for this purpose. It should switch much slower than the front oxygen sensors. If at any point the PCM detects that the post-catalyst o2 sensor is switching too rapidly (indicating no change between the inlet and outlet of the catalytic converter) it interprets this as a catalyst that isn't functioning properly.


Bank 2 is the side of the engine that has cylinder #1.


Symptoms of a P0422 DTC may include:
Increased tailpipe emissions
MIL (Malfunction Indicator Lamp) illumination

Potential causes of a P0422 code include:
Bad or non-functional catalyst
Engine operating out of optimal air:fuel ratio


Possible Solutions: Catalytic converters contain precious metals like platinum, palladium, rhodium among others. Basically, the cheaper the cat, the less precious metals used. It should be noted that there are some automobile makes that are very finicky when it comes to catalytic converters and the logic that the PCM uses to monitor them. Just because the parts guy says it will work doesn't mean that it will. The reason is that the engineering of the vehicle was done with a high quality catalyst in mind and it can't be replaced with a low cost catalyst. There are also different kinds of catalysts. Some makes will allow for a cheaper catalyst while others simply will not. Toyotas & Subarus are the most notorious for this. Subarus require CARB certified catalysts to keep the check engine light off and won't tolerate an aftermarket catalyst, no matter how expensive.


So basically if you have a recurrence of this code after replacing the catalyst with an aftermarket catalyst, this may be your problem. If you have this code and haven't replaced the cat, there's basically two likely causes: The catalyst is no good, or the engine is running out of optimal air:fuel ratio. A tune up or engine repair may correct it. Otherwise you'll need to replace the catalyst.


Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

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well since they are located in the exhaust system start in engine compartment at the exhaust manifolds and and work your way back. depending on engine size and whether or not the exhaust is dual or comes together as one the best spot to check is at the catalyst. see there are different types and could be one bigger one or 2 smaller ones.... if one big catalytic converter should have 2 possibly 3 hO2 sensors and if you have 2 smaller catalytic converters you should have 4 hO2 sensors.... to take them out you want your exhaust plenty warm cuz things expand and is easier to remove them. before catalyst is your upstream which helps with fuel delivery and after is your downstream whichs monitors catalyst function. ford uses hO2 sensors which is heated O2 sensors. hope this can help you

check your ground on the engine

Check the temperature sensor wire, it may have need knocked of or damaged do to corrosion. The temperature sensor should be located on the intake manifold by the thermostat house. Once the rise issues has been addressed the check engine light should go off after the the start up. Good luck and keep me posted. Be glad to help you get your car running 100 % again.

P0420 = Catalyst System Efficiency Below ThresholdCatalyst System Efficiency Below Threshold. This means that the secondary O2 sensor detects that the catalytic converter isn't working as efficiently as it should. This engine code can be triggered by any one of the following:

1.) The catalyst in the catalytic converter is cracked, clogged, or otherwise damaged.
2.) The secondary O2 sensor is malfunctioning.
3.) There is an exhaust leak.
4.) The computer unit is faulty

check for fuel prusser from 40-55psi if its good change the fuel regulator

Remove and clean the mass air flow sensor and see if it makes any difference. (can be cleaned with carb cleaner and Q tip)

Being that is so intermittent I would lean toward vapor lock as the culprit. Unless your check engine light comes on then it's a sensor or something else.

You can learn more about vapor lock here:
http://en.wikipedia.org/wiki/Vapour_lock

hope this helps and good luck