I have a 2000 S-10 with 41K miles on it. It failed the emissions inspection because 3 of the sensors haven’t completed the self test. I changed the battery last year and it’s been driven around town, on the highway, and even from Dallas to Austin since then. The Catalyst
Monitor, Evap System Monitor, and O2 Sensor Heater are the ones that show incomplete on the test. There are no codes in the computer and the check engine light hasn’t come on. I took it in to the shop, but they’re baffled and have recommended a new computer. Has anyone seen this before?
Had the same in a '97 s-10 Blazer, fixed by cleaning up a common ground. Not sure if the 2000 s-10 is identical wiring but they are the same gen. chassis/drivetrain. HTH
Thanks, I’ll pass this along to the mechanic and see what he can find.
Make sure the engine computer is getting power when the ignition is off, to retain memory.
Check fuses.
It’s maintaining power, otherwise more sensors would show incomplete. Thanks for the suggestion.
Mention of fuses reminds me that I recall that the s-10 powers OBD port through the cig. lighter fuse. Are your lighter socket(s) (some have 1 some have 1+2 aux. outlets) working? If not this SHOULD cause a general inability to read all codes but you never know, stranger stuff happens.
Here’s an update on the problem. It’s been in the shop for two days. They’ve changed and reprogrammed the computer, and driven it several times to reset the sensors. Nothing’s worked. They’re going to try it again tomorrow and see what happens. I’m hoping I’m not putting money into a truck that’ll be a trade-in by the end of the month, but it’s not looking good.
Sorry I couldn’t help more. So even w/a new computer they are still not getting readiness on the same 3? Really leads me to believe it’s a wiring issue somewhere (yeah, somewhere is a big help I know). Not sure about TX but in some states you can still get a pass on emissions inspection if you have spent $xx trying to resolve an issue, regardless of the outcome. In NY it’s $450 parts/labor/tax or parts only if you DIY.
OK a few more things. Have the mechanics determined that the truck is indeed going into closed loop driving? This is basic to me but it needs to be mentioned to get further w/this. If it’s not been determined then they should check. If not going closed loop then suspect the engine not getting up to normal hot operating temp. Suspect the thermostat not allowing getting up to full temp or temp sensor (there are 2 on this truck if it is a 6 cyl. 1. sending unit for dash gauge - located on driver side head, between the #3 and #5 spark plugs, wiring connector contains only one wire & 2. sensor for ECU - located on the intake manifold, right next to the thermostat, wiring connector contains two wires. So you see #1 could be telling you all is OK, and it maybe if T-stat is good but #2 could be telling the ECU otherwise) not telling the ECU the engine is at full temp. So in looking for a common parameter in your failure areas and if not going into closed loop a common seems to be engine temp. Check / replace thermostat (along w/flush and pressure check of the system AND the cap, the OE caps are known to go bad on these) and check what the temp. sensors are reporting and check the actual coolant temp independent of the sensors. Some links for info.
http://www.obdii.com/drivecycle.html
How to interpret the test results to determine why a test might not be ready
http://service.gm.com/gmspo/mode6/
this would be you if 6 cyl. http://service.gm.com/gmspo/mode6/pdf/2000/2000file15_6.pdf
Below from (under heading “readiness flags”)
http://www.obdii.com/articles/OBDII_and_Emissions_Testing.html
The Environmental Protection Agency (EPA) realized this shortcoming in current generation OBD II systems. So, when it created the rules for states that want to implement OBD II testing in place of tailpipe dyno testing, it allows up to two readiness flags to not be set prior to taking an OBD II test on 1996 to 2000 vehicles, and one readiness flag not to be set on 2001 and newer vehicles. You can use the AutoTap OBDII scantool to check that your readiness flags are set before having your vehicle emissions-tested. This can save you the aggrevation of being sent off to drive around and come back later.
So I think if you can get rid of just one lack of readiness they can pass you. Below is the NY inspection guidance, check the last sentence 
New York has adopted the federal Environmental Protection Agency (EPA) guidance concerning readiness during OBD inspections. A vehicle will fail the NYVIP OBD II inspection if enough monitors are reported as “Not Ready.” Generally, OBD II vehicles from model year 1996 to model year 2000, inclusive, will fail if 3 or more monitors are set as “Not Ready;” while model year 2001 and newer vehicles will fail when 2 or more monitors are reported as “Not Ready.” There are a few vehicle exceptions to these guidelines, but the NYVIP inspection software makes these cases transparent to the inspector. Consistent with federal guidance, the three continuous monitors are not considered in the readiness determination as these are anticipated to be Ready. In summary, the readiness status of all supported, non-continuous monitors are only considered in making the OBD II pass or fail determination. For most gasoline-powered vehicles, this involves 3 to 5 monitors. It is not always required, nor practical in some cases, for ALL monitors to be set as “Ready” for the NYVIP inspection. This condition is, however, highly recommended for the confirmation of effective repairs. In general, the EVAP and CAT monitors will be the most difficult monitors to set as “Ready.”
did it get fixed, what was it??
The final solution was a new computer and a lot of driving. They drove it for two days before it reset enough to pass.
I’m SURE the air in Texas is MUCH cleaner tonight and that the money you spent to make a computer happy was worth every penny…