Can’t pass emissions test even though codes pass.

The car will not pass the emissions test. All of the codes seem to pass, but the computer doesn't go into Computer Ready status. No one can figure out why.
Experienced mechanics share their insights in answering this question :
Hello,
To get the readiness monitors to pass it requires driving the sometime in a different fashion than what you’re used to. To start, the fuel tank needs to be between 3/4 and 1/4 tank and the vehicle must be driving on the freeway at 55 MPH (set the cruise control) for about 5 miles. When you get off the freeway, pull over to a safe location shut off the engine and restart it. Let the car idle for a 2 minutes and get back on the freeway and return home doing 55 MPH. The reason for 55 MPH is that was law of the land when all this was written and the parameters were set. If you live in a large metropolitan area, you may need to go do this at night like 10 pm to be able to cruise at 55 MPH. Another great resource, if you know which readiness codes are not set, is to search the web for "GM drive cycle".

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

Faulty sensors: A failing oxygen sensor or bad mass airflow sensor can trigger your “check engine light.” Other issues: A gas cap that`s loose, cracked, or otherwise ill-fitting can cause an emissions test failure. Waiting too long between oil changes or replacing your engine air filter can also be the culprit.
What kind of penalties are there surrounding smog inspections? If you car fails a smog inspection or if you fail to get a smog inspection once every two years, then you will not be allowed to renew your car`s registration with the DMV. As a result, you will not be able to legally drive that car on the street.
Your vehicle`s emissions computer is programmed to process information based on it`s required fuel octane. The Low-Down on High Octane Gasoline: Are you tempted to buy a high octane gasoline for your vehicle because you want to improve performance? If so, the recommended gasoline for most cars is regular octane (87).
DON`T clear any Data Trouble Codes using a scanner, hoping to pass the emission test. If you erase the Data Trouble Codes and then take the vehicle in for emission testing right away, it will be “Rejected”. Clearing the Data Trouble Codes erases all of the OBD-II system`s memory settings.
Yes, a car should still pass emissions with a pending code.

There is a difference between pending codes and hard codes. Pending codes mean that there may be a problem and your vehicle`s computer needs to run more diagnostics.

Emissions Test Failure

If the O2 sensor is bad, your vehicle won`t pass an emissions test because there will either be too much or too little oxygen in the exhaust, which affects the other emission gas levels.

In most cases, two drive cycles are required, separated by a cool down period.
BAR-OIS allows one incomplete continuous monitor.
Here`s something you probably don`t know: after clearing the car`s computer you will need to drive for about 50 to 100 miles. As you drive your car the computer will monitor all the sensors and register the results.
Higher-octane juice won`t reduce pollution or emissions at all, according to a study recently done by the American Automobile Association. Fewer than 20 percent of the cars on the road today have engines designed specifically to burn premium gas, which is what they should be running.
Based on its oil-refinery modeling, the group found that producing higher-octane fuel would increase an oil refinery`s emissions by 6 percent — an increase that is minor when compared with the balance of emissions from fuel production.
The only way to clear a PDTC is to fix the underlying problem with the vehicle that originally caused the PDTC and its corresponding DTC to set, and then allow the vehicle sufficient drive time to re-run the monitor that identified the problem in the first place.
Here`s something you probably don`t know: after clearing the car`s computer you will need to drive for about 50 to 100 miles. As you drive your car the computer will monitor all the sensors and register the results.
Driving 4-7 days in city and highway usually resets the monitors. Vehicle must meet basic operating criteria and complete its manufacturer drive cycle for a particular monitor.
A defeat device is any motor vehicle hardware, software, or design that interferes with or disables emissions controls under real-world driving conditions, even if the vehicle passes formal emissions testing.
Driving 4-7 days in city and highway usually resets the monitors. Vehicle must meet basic operating criteria and complete its manufacturer drive cycle for a particular monitor.
These emissions can be reduced by making process changes (such as modifications to the combustion process) or by installing air pollution control equipment (such as selective non-catalytic reduction (SNCR) or selective catalytic reduction (SCR)).

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Can’t pass emissions test even though codes pass.
ANSWER : Hello,
To get the readiness monitors to pass it requires driving the sometime in a different fashion than what you’re used to. To start, the fuel tank needs to be between 3/4 and 1/4 tank and the vehicle must be driving on the freeway at 55 MPH (set the cruise control) for about 5 miles. When you get off the freeway, pull over to a safe location shut off the engine and restart it. Let the car idle for a 2 minutes and get back on the freeway and return home doing 55 MPH. The reason for 55 MPH is that was law of the land when all this was written and the parameters were set. If you live in a large metropolitan area, you may need to go do this at night like 10 pm to be able to cruise at 55 MPH. Another great resource, if you know which readiness codes are not set, is to search the web for "GM drive cycle".

KOEO test code 332
ANSWER : Hello there, A few different things can cause insufficient EGR flow. The most likely are:

a stuck closed EGR valve
a failed EGR valve solenoid
faulty oxygen sensor
low fuel pressure
exhaust leak

These can also result in the reduced power output you have noted.

A qualified technician, such as one from YourMechanic, will be able to diagnose your Check Engine Light and perform any repairs required.

Want to pass emissions testing, but I have a P0400 code for my vehicle. 2000 Nissan Altima
ANSWER : Hi there – the P0400 code you have suggests a problem with the Exhaust Gas Recirculation system of your car. Given your mileage, this malfunction could be a clogged EGR valve or tube, solenoid or leaking exhaust gas tube. I recommend an EGR system inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.

My car doesn’t pass emissions because the catalyst system is below threshold, and the exhaust gas recirculalation is insufficient.
ANSWER : Hi there. The Engine Gas Recirculation (EGR) valve could be sticking or full of deposits from the exhaust system. Remove and clean the EGR valve before replacing it to see if the system will begin to operate. The oxygen sensors that measure the catalytic converter is picking up an uneven measure. This says that the catalytic converter is below threshold, but if the system is too lean, the same code will come up. Simply fixing the EGR valve will fix the emissions and should make the engine light go out. I recommend driving the vehicle for a week after the light goes out before heading to the emission station.

Billing question sent to CS for the cost of fixing the vehicle to pass emissions.

failed emission test at Division of motor Vehicle
ANSWER : Hey there. The three different Check Engine codes you mentioned (P0420, P0133, and P0171) would need to be diagnosed first to see why they are stored in computer memory. You will need the mechanic clear the codes and test them in order to have each addressed. With the Check Engine cleared, you should be able to pass the emissions test.

I have a Code P0601 on the PCM. I replaced the PCM, and now I have a code P0118, code P0123, and code P0193.
ANSWER : Hi there, the short answer to your question is no . A PCM with a P0601 (which is a memory module error in the PCM) cannot reliably retrieve codes for the codes you list (P0118 – coolant temp sensor, P0123 – throttle position sensor, P0193 – fuel rail pressure sensor.

Most likely, the P0601 prevents the PCM from getting any codes from the engine sensors. The memory module error may cause in data corruption for collected sensor values, lose of data over multiple sampling periods, or failure of the data collection to work at all. Replacing the PCM was a necessary expense.

If you need assistance with the "new" codes, I would recommend having a Check Engine Light inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose the new error codes and get an accurate assessment of the repairs needed.

Service engine warning, MAF code and O2 sensor code, along with check suspension light are turned on
ANSWER : Hello, it sounds like you have quite a few things going on. I am going to do my best to break them down for you.

First if the engine is very loud when idling and the belt has already been replaced, there may be an issue with the tensioner or idler pulley.
Next, the Navigator is known for needing service to the air suspension system as it gets up in miles, the most common causes of these are the air struts themselves have failed, or one of the air lines has a leak.
Lastly, if the O2 sensor and MAF are continually coming back after the sensors have been replaced, the most common cause would be either an exhaust leak or a vacuum leak.

Qualified technicians such as the ones at YourMechanic will be able to diagnose these issues and recommend the best path to repair, starting with a diagnosis of your warning lights.

Emissions test failed with a new gas cap
ANSWER : Hey there. This may be related to other possible malfunctions in your EVAP system, such as a faulty vent valve solenoid. The EVAP system prevents fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system collects and temporarily stores the fuel vapors in the charcoal canister. The charcoal canister is filled with activated carbon pellets that can absorb the fuel vapors.

When the engine is running, the fuel vapors are purged from the canister and burned in the engine. The vent control valve (solenoid) controls the flow of outside air in and out of the charcoal canister. When this solenoid is not working properly, this may cause the tank to fail to expel the vapors as it is designed to causing the failed emissions test. If you would like to have the car scoped out, a certified professional from YourMechanic can conduct a comprehensive diagnostic on your car before you take it in for another emissions test.