Question about 1994 Mercury Grand Marquis

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What does the code CO mean on the display panel? Do I have to replace something in the vehicle? And if so, what needs to be replaced?

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I think it means circuit open.

look in owner manual

Posted on Oct 20, 2010


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What does it mean when check engine light is flashing

get it serviced USUALLY before it blows up

Nov 21, 2015 | Cars & Trucks

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I have a 2002 yukon xl 1500 slt 5.3 and I took it to auto zone gave me a code of p0420.Do u have any suggestions on this code?And what can I do about it?I don't have any money and I need my vehicle.Can you...

P0420 GMC - Catalyst System Low Efficiency Bank 1 ' Add Comment
Possible causes
- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Powertrain Control Module (PCM)
What does this mean?
Tech notes
As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.
What does this mean?
When is the code detected?
If a condition exists which causes the Powertrain Control Module (PCM) to detect excessive Bank 1 HO2S #2 activity outside of an acceptable range for an extended period of time, the PCM will set the P0420 code. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0420 GMC Description
In order to maintain a reasonably low emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The Powertrain Control Module (PCM) monitors this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than that produced by Bank 1 HO2S #1.

Mar 31, 2015 | 2002 GMC Yukon XL

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The engine light is on, it is a honda odessey 03

Means you need to have the vehicle scanned for fault codes and you have an emission related problem

Oct 09, 2014 | 2003 Honda Odyssey

1 Answer


Your vehicle will still run if the exhaust is off. This does not mean that the catalytic converters are bad or good. If your vehicle was throwing codes before you removed the exhaust there is a good chance they need replaced, or if the exhaust coming out of the tailpipe smells bad they may need replaced as well.

Generally, Catalytic converters will last the life of your car unless they are damaged with something other than normal wear and tear.

Sep 07, 2011 | 2003 Ford Escape

1 Answer

Engine light came on while what could be the problem

Not something that can actually be guessed at but i'll give it a shot. If the vehicle is running fine it's an evap or o2 code. Which means you need to either tighten your gas cap or replace it for the evap code. Th o2 one means the o2 sensors need to be replaced.

The better option is to take the vehcile and have a scanner hooked up to it to determine what is actually going on.

Mar 08, 2011 | 2004 Ford Taurus

3 Answers

What does it mean if the engine light is blinking?

depress the HEAT & AC button to receive the codes displayed on the cluster. The codes you will need to write down and get back with me to see what the problems is

Feb 23, 2011 | 1998 Cadillac Eldorado

1 Answer

What does a c on the dic mean?

Your vehicle has a Driver Information Center (DIC).
All messages will appear in the DIC display located
below the speedometer in the instrument panel cluster.
The DIC buttons are located on the instrument panel,
to the left of the instrument panel cluster.
The DIC comes on when the ignition is on. After a short
delay, the DIC will display the information that was
last displayed before the engine was turned off.
The DIC displays trip, fuel, and vehicle system
information, and warning messages if a system problem
is detected. The bottom line of the DIC shows the
shift lever position indicator. See Automatic
Transmission Operation on page 3-23
for more
If your vehicle’s DIC has these features, the compass
direction and the outside air temperature may also
display on the DIC when viewing the trip and fuel
information. The compass direction appears on the top
right corner of the DIC display. The outside air
temperature automatically appears in the bottom right
corner of the DIC display. If there is a problem with the
system that controls the temperature display, the
numbers will be replaced with dashes. If this occurs,
have the vehicle serviced by your dealer/retailer.
The DIC also allows some features to be customized.
See DIC Vehicle Customization on page 4-66 for
more information.

Sep 05, 2010 | 2002 Buick Rendezvous

1 Answer

Battery died and had to get it replaced somewhere besides a dealership-radio will not work-digital panel does not even come on-nothing-2003X-type 3.0, AWD-any help would be appreciated!!!

If there is nothing at all then it's most likely a fuse gone, (could have something to do with battery failure?) could be fuse F72 in passenger bay fuse box. If it has the word 'code' displayed it needs the code entered. There are other things that you will also need to do, after a battery replacement.
Full fuse details, radio code details, and drive cycle details can be found on

May 19, 2010 | 2003 Jaguar X-Type

1 Answer


The 420 code means you need the catalytic converter replaced. The TCS means Traction Control System. The green key is the theft system. Both lights MAY have nothing to do with the car shutting off Sometimes those lights will display when something elese makes the car stall. Perhaps a faulty crank sensor or the cat is so clogged its stalling out the car.

Mar 08, 2010 | 1999 Acura TL

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