At wits end here.have failed emissions for the 4th try in CT. Have driven the car well over 700 miles between the first and last test. 5 sensors are failing, which makes me question if the maybe my computer went bad. Have tried disconnecting the battery and letting it sit for 3 hours thinking a reboot might help . Drove an additional 220 miles after that. Have researched drive cycles, and while not done altogether, have tried through the miles to hit each piece. any ideas or thoughts of what is causing this would be appreciated. Is there something in common with the not-ready's? See emission test form below.
Thanks!

 

From what the picture looks like it shows 5 diagnostic trouble codes, yet you don't have check engine light on at the time of the test. You can get a hand held scanner and look up the codes yourself (about $50 - $100 for store bought scanners) or take your truck to a shop that has a scan tool and will tell you the active powertrain codes, any freeze frame data associated with said codes, and any history codes that might be present.


I wish I could be more helpful as we don't emissions testing here in Florida, but I do hope this helps. Also, disconnecting the battery or hitting erase button on a scanner will clear all readiness monitors, codes, and freeze data; which can do more harm than good.

 

Took mine about 3 months to get it ready. Ran the drive cycle 20 times. Drive a company car most of the time plus I have two other vehicles. Would take it out twice a week for a couple of drive cycles at night till it was ready.

 

Performing the General Motors Driving Cycle will force all monitors to run and complete their tests. All 8 steps must be performed, but they do not have to be performed in order. Each step must be performed exactly as written, or the monitor will not run and complete its tests. The entire drive cycle can be completed in about 15 minutes.

 

On the report the engine temp is 113. Is it normally that low?
I was told it needs to be at "normal operating temperature" for ECU to run the tests, and make the monitor say "OK".
The thermostat is usually around 195. My Blazer was running 141-150, and would not complete the last four.

 

That's a problem. The stat should begin to open at 195F, and they usually regulate very close to 200F. Don't rely on the dash gauge, they are not known for their accuracy Use a scan tool to check ECT, (engine coolant temp).

Step one requires a cold start up. As soon as step one is complete, perform step 2. Steps three through 8 require normal coolant operating temperature, (~200F).

 

I wanted to give an update as it took 4 months for me to piece it together. i found one post somewhere about the engine coolant temperature sensor. it lined up: my temp gauge had not been working for about a year, and most recently my fuel milage dropped off significantly(from normal about 13mpg to 9mpg or so).
the issue is the ECT sensor (engine coolant temperature sensor), which in the 1999 blazer controls both the dashboard temp gauge and the computer (i read in some years, i think earlier, there is a second gauge on top of the thermostat, not sure how that works). because the temp reading was low, the computer never registered that it should be recording data about the engine. so it threw it all out. i replaced the ect, ran 250 miles, and it passed emissions first try.
here are pics for where it is located:
I found that it was very accessible after removing the air intake. you dont need to remove it completely - keep wires inplace, but unbolt from above the airfilter, and on top of the air intake manifold, and move it aside a bit. this will give you much more room to work.
it also may be a wiring issue. there should be a 5v dc drop between the wires. i did NOT test this, the part was cheap enough i went with that first. but it may be wiring. you can test by taking off the electrical connection and use a multimeter. as the engine gets hot, the ect drops resistance and allows more voltage to flow (really amps, but who is counting).
i am now going to blurt out a bunch of keywords, in hopes that others trying to google this problem find this post:
catalyst: not ready
EGR System: not ready
Evaporative System: not ready
Heated Catalyst: not ready
oxygen sensor: not ready
oxygen sensor heated: not ready
secondary air system: not ready
emissions fail
emission not ready
emission inspection
good luck to all, hope it helps

 

You are correct about the sensor. The data is used by the PCM for engine controls, and the dash gauge. It is a thermistor and resistance values change as temperature changes. The first sign of trouble would be your dash gauge reading low, (should be ~200F). Connecting a scan tool and monitoring coolant temperature would instantly spot the problem. If the sensor is not calibrated correctly, but still within its acceptable range, it would not set a DTC, or turn the SES light on. The monitors that were incomplete will not run if coolant temperature is too low. You can check the accuracy of the sensor by checking actual coolant temperature using a thermometer, or an infra red (laser) thermometer. You can also compare ECT, IAT & ambient temperature to make sure all three are indicating the same temperature. After the vehicle sits for 10 to 12 hours, and before starting the engine, is when the readings need to be taken.


Oxygen sensors are an extremely accurate way of measuring fuel mixture, but the PCM ignores them in open loop, (when the engine is first started). During open loop the PCM uses data from MAF, MAP, ECT, IAT, TPS, BARO for adjusting fuel mixture. When coolant temperature is low, the PCM adds more fuel. Fuel mileage and performance suffers substantially during open loop. Engine coolant temperature is one of the triggers for the PCM to switch over to closed loop. Once it reaches a certain temperature, the PCM switches over and uses the oxygen sensor data to adjust fuel mixture. If the ECT indicates coolant temperature is low, either due to a faulty sensor, or from the coolant temperature not rising enough, (thermostat stuck open etc) the PCM will not switch to closed loop.