Evap and Catalyst not ready?

2005 CHEVROLET COLORADO

190,000 MILES • 3.5L • AUTOMATIC

JAMESPAUL

MEMBER
1 POST

I recently put another battery on my truck. Three days later I went to get it inspected it failed. They told me it was cuz I recently took the battery cables off the battery. They told me the evac and catalyst was not coming to ready and that I needed to drive the truck more and do some drive reset s. It's not throwing any codes but I did everything they told me to do and it still the event and Catalyst will not come to ready state. In Texas you can have one system that does not come to ready but not two therefore it's not passing inspection. I have driven it over 500 miles I'm at my wit's end. Thanks James

Sep 20, 2026 at 6:46 PM

STEVE W.

✓Experienced Mechanic
15,337 POSTS

EVAP can take a while to set, there are specific things that have to happen in the drive cycle. The same is an issue for the cat monitor.

This is the drive cycle for the EVAP test -
The difference between start-up engine coolant temperature (ECT) and the intake air temperature (IAT) is less than 14.4°F.
The barometric pressure (BARO) is more than 74 kPa.
The start-up ECT is between 39-86°F.
The start-up IAT is between 39-86°F.
The fuel level is between 15-75 percent.
The battery voltage is between 11-18 volts.
The fuel level does not increase more than 10 percent during the drive cycle.
The vehicle has been driven at least 3.2 miles during the drive cycle.
The ECT is more than 158°F.

BUT the system has to run this cycle, then the vehicle has to set without running or being touched for at least 17 hours. Then it has run a second time and then set for 17 hours again. On the third trip, if it runs the cycle it will finally set the monitor to yes.

For the cat monitor to switch to ready -
The engine has been running longer than 10 minutes.
The barometric pressure (BARO) is more than 72 kPa.
Engine coolant is at operating temperature, 157-257°F.
The intake air temperature (IAT) is between -4 and +176°F.
The engine is in closed loop fuel control.
The battery voltage is more than 9 volts.

For this one you would start the engine drive it until it is at operating temperature, then shut it off. Now wait a couple minutes and start it back up and drive it for about 15 minutes. However, if there are any codes, even pending codes, the cat monitor may not run. It can also abort the test if there is a load change like the AC turning on or similar.

Sep 20, 2026 at 8:49 PM

Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.