Codes P0420 & P0442

[BluYa76]

Hey Charlie,

I'm not sure what to look for. I've looked up the codes and I'm kind of clueless what to look for now.

Background: car is a 2002 Grand Prix GTP 3.8 Supercharged

I've replaced the gas cap because that was recommended to me with no change. Now the check engine light will come on with these codes (but only one code will be set at one time, never both) when the car is first started when cold for the day and they will pop on usually with in the first ten minutes. They won't come on after the car's warmed up and have been cleared out with my scanner. That's the gist of it. Any help would be greatly appreciated.

[JerzeyGT]

Im not Charlie, but code P0420 is usually low catalytic efficiency, there is restiction somwhere or the o2 could be reading slow ....

[wreckwriter]

P0442 is a vacuum leak I believe.

[JerzeyGT]

Here is the bulletin from GM... This came up when I put in that code for your year and vehicle...

xTooltipElement
Service Information 2002 Pontiac Grand Prix | Grand Prix (VIN W) Service Manual | Document ID: 824194
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#00-06-04-011A: Info - Evaporative Emissions DTC P0440, P0441, P0442, P0446 - (Oct 4, 2001)


Subject: Evaporative Emissions DTC P0440, P0441, P0442, P0446


Models: 1996-2002 Passenger Cars and Trucks

With Enhanced Evaporative Emissions Engines

Except 1998-1999 Chevrolet Prizm




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This bulletin is being revised to add model years and diagnostic enhancements. Please discard Corporate Bulletin Number 00-06-04-011 (Section 6-Engine).


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Enhanced Evaporative Emissions testing of 1996 and newer vehicles with enhanced evaporative emissions requires more stringent testing of the fuel system for evaporative emissions leaks. Vehicles with this system use an on-board diagnostic module (i.e. Powertrain Control Module (PCM) or Vehicle Control Module (VCM) as the controller. For the balance of this bulletin, we will refer to either of these components as a module.

Enhanced Evaporative Emission tests may be performed by the vehicle's module when specific conditions are met. These conditions are determined by the calibration within the module. These calibrations are vehicle platform and engine family specific.

When the key is turned to the start or run position, the module checks the output of various sensors on the vehicle to determine when and if the Evaporative Emissions tests should be run. Refer to Engine Controls sub-section of the appropriate Service Manual for specific DTC information.

Some of the most widely used parameters are listed below:

The Barometric Pressure (BARO) is greater than a specified kPa (psi).
The system voltage is between 10 and 18 volts.
The intake air temperature (IAT) is within specified temperature values.
The engine coolant temperature (ECT) is within specified temperature values.
The ECT and IAT are within specified temperatures of each other when the vehicle engine was started.
The fuel level sensor indicates the fuel level is greater than a specified % of empty and less than a specified % of full. (For a 76 L (20 gal) fuel tank, a fuel level of more than 11 L (3 gal) but less than 64 L (17 gal) or as specified in the calibration).
Some platforms such as the Alero and Grand Am, use a miles driven check as well.
For the ECT and IAT to be within the specified temperatures of each other at the time of engine start-up, the engine will have to be in the non-running condition for a long enough period of time for the engine coolant temperature to drop from its normal operating temperature down to roughly 30°C (90°F). This could take several hours.

When the control module determines that the above conditions are met, the module tests for a leak in the EVAP system by:

• Electrically closing the vent valve in order to seal the system.

• Electrically opening the purge valve which allows the running engine to draw a vacuum on the fuel tank.

• The module then closes the purge valve, resealing the system.

• The module then monitors the fuel tank pressure sensor and determines:

- If vacuum was achieved.

- If a leak is present, how large the leak is.

- If vacuum was not achieved.

• If one of the above tests fails, the module remembers that the system failed the test.

• If the module sees a failure of the EVAP test for two consecutive tests, the module will set a trouble code for EVAP leak (DTCs P0440, P0442, or P0446).

Important: If the PCM is completing the EVAP diagnostic, filling of the fuel tank cannot be completed as the vent valve will be closed and the fuel dispenser nozzle will sense the pressure build-up and shut down. This is the expected result. No parts should be replaced as nothing is faulty. To keep from encountering this situation, it is imperative all customers and dealership personnel be advised NOT TO FILL THE FUEL TANK WITH THE ENGINE RUNNING. If the condition is encountered, turn the ignition to the OFF position for a minute. This will allow the PCM to go to sleep completely, thereby opening the vent valve.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


© 2009 General Motors Corporation. All rights reserved.

[GRRRR8]

You have a cat issue and an evap issue, BUT I would fix the evap code 1st and retest as if the purge was stuck open it would effect cat efficiency.

[BluYa76]

You have a cat issue and an evap issue, BUT I would fix the evap code 1st and retest as if the purge was stuck open it would effect cat efficiency.

Well the cat code really does not surprise me since I'm running the car with a straight through pipe with no cat and an O2 simulator. The vac leak is a little more of a pain in butt, since I'm not sure what to look at.

[Panzer Leader]

Well the cat code really does not surprise me since I'm running the car with a straight through pipe with no cat and an O2 simulator. The vac leak is a little more of a pain in butt, since I'm not sure what to look at.

I just have to ask one question, Why didn't you say that in your initial post?

[BluYa76]

I just have to ask one question, Why didn't you say that in your initial post?

Well cause I was not sure what the code ment when I looked it up and I forgot to mention the cat-less down pipe cause I was going on 30 hours of no sleep (my ignorance simply put).

[ft2lewis]

what kind of simulators are you using

[American muscle]

I keep getting the p0420 code even after I changed the sensor, is my catylic converter bad, and Is it worth it if I get a new exhaust system with a bit more roar