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OBD-II never comes up ready - HELP!

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Old 03-13-2010, 02:04 PM   #1
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Exclamation OBD-II never comes up ready - HELP!

1997 S10 Blazer LS 4.3 V6 4-door 4wd, in New Jersey USA.

I'm overdue to state inspection. I keeps failing for OBD-II readiness (not ready).

I've got an AutoXray EZscan 5000 and find that the darn truck is messed up!

Readiness tests results change frequently It's like the ECU is losing it's data, but it never loses power. I haven't disconnected the battery nor cleared the codes.

My Readiness tests results:
MIL Status: OFF
Misfire Monitor: Completed (always)
Fuel System Monitor: Completed (always)
Comp. Component: Completed (always)
Catalyst Monitor: Not Completed **
Heated Catalyst: Not Supported
Evaporative System: Not Completed **
2nd Air System: Not supported
A/C Refrigerant: Not Supported
O2 Sensor: Completed *
O2 Sensor Heater: Completed *
EGR System: Not Completed ***problem***

* = These tests are complete shortly after driving about 10 miles, but reset to not completed after every shutdown and restart.
** = These tests go complete after a long trip (100+ miles), but reset to not completed after shutdown and restart.
*** = The EGR System NEVER comes ready.

I've never had this problem before with the OBD-II not ever coming ready. The truck is a little hard starting, especially when the engine is warm. It starts up better the colder the weather is.

So, with this limited information, can anyone give me any direction? Is my ECU possibly cooked? Should I diagnose an EGR problem? Is it normal for so many of these tests to reset when restarting the engine? If that's true, I'll never pass inspection - 'cause they shutdown the engine to hook up the computer, then restart and monitor.

Any chance this is a common problem with these trucks?

Help - please - I'm desperate at this point.
Old 03-14-2010, 02:00 PM   #2
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Re: OBD-II never comes up ready - HELP!

make sure all fuses are good... thats a start. its possible there is one blown and keeping the ECU from retaining its memory... other than that, find a used matching ecu and try your luck with that. Sounds like its in the computer or with the power getting to it...
Old 03-15-2010, 10:15 PM   #3
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Re: OBD-II never comes up ready - HELP!

I got a tip from the guys on blazerforum.com that my issue might be the temperature sensor circuit, or something related causing the computer to read the engine never coming up to operating temperature.

That sounds like a reasonably easy fix. So, here are my questions, then:

I started researching temp sending units. Looks like my 97 has 2 of 'em:
* Temperature Switch
* Coolant Temperature Sensor

Which one, or both?
I think the coolant temperature sensor is on the driver side of my engine, in the head between the #3 and #5 cylinder spark plugs.

But, I have no idea where this temperature switch is. In fact, I'm not sure what the temp switch is for. I read somewhere that the coolant temp sensor is for the dash gauge and the temp switch is for the PCM (or ECU or whatever we call the engine computer).

Should I replace both?

I'm thinking of replacing the thermostat, too.
I have noticed that the heat inside the cabin is not as warm as I remember in years passed. And, the temp gauge on the dash does always read a bit low.

I don't want to replace parts needlessly, wasting money, but I do want to fix this thing completely, correctly, and quickly. So, I don't mind swapping out a 20 dollar sensor if it's not a huge pain in the arse.

Please, if possible, lemme know where this temp switch is, what it's for, and if you think it might be a good idea for me to replace it or not.

Thanx for any help. I do appreciate it!
Old 03-16-2010, 08:41 AM   #4
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Re: OBD-II never comes up ready - HELP!

you have got a sensor right by your thermostat not sure what it is but it dose go in the coolant passage.
Old 03-22-2010, 05:32 PM   #5
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Re: OBD-II never comes up ready - HELP!

OK, just for everyone's sake, I found the location and identification of the two sensors related to engine temp are:

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.
Old 03-22-2010, 05:36 PM   #6
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Re: OBD-II never comes up ready - HELP!

OK, thought I'd bring this post up to speed. Temp is/was definitely an issue.

I decided to take a pragmatic approach to this. Fix/Replace one thing at a time, rather than the shotgun approach of replacing everything. This way, if I ever do fix it, I have a clue as to what the solution was. Plus, I hate too many variables. If the symptom changes, it's so much harder to pinpoint the cause.

So, I replaced just the thermostat. I flushed the cooling system, refilled it, and bled the cooling system. Swapping out the thermostat was pretty darn easy.

Now, engine temp runs around 195 degrees F. Temp gauge in the dash reflects that, so I think the sensor/sending-unit for the dash is working well enough. My AutoXRay 5000 is able to monitor engine temp, so I think the sensor for the ECU is working too, as it reads between 194 - 197 degrees F after 5-10 minutes of engine warm up.

Now, things are better, but still not READY:

My Readiness tests results:
MIL Status: OFF
Misfire Monitor: Completed (always)
Fuel System Monitor: Completed (always)
Comp. Component: Completed (always)
Catalyst Monitor: Completed (always)
Heated Catalyst: Not Supported
Evaporative System: Not Completed **
2nd Air System: Not supported
A/C Refrigerant: Not Supported
O2 Sensor: Completed (always)
O2 Sensor Heater: Completed *
EGR System: Completed *

* = comes up completed, but not before at least 20 minutes of driving
** = never comes up completed!

NOTE: no current trouble codes.
I do have one old/historical (pending) trouble code [P0894] Transmission Component Slippage. I've gotten that intermittently for years. I'm not currently concerned with it.

It seems the evaporative system test is still not completing. I'm not jumping up and down just yet. I'm going to drive the truck for a few more days. I did the t-stat replacement just last Thursday night. So, perhaps the ECU needs a little more time to collect data. If the system doesn't come up ready by Friday, I'll panic again.

If anyone has any ideas on what I might want to look at, to see what's holding up the Evap System, or why it might be sluggish or unable to come ready, man, I'd really appreciate the knowledge.

Thanks everyone, and I'll keep ya posted!
Old 03-23-2010, 04:10 AM   #7
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Re: OBD-II never comes up ready - HELP!

Knowing the ODBII will help you.
http://www.obdii.com/drivecycle.html
Old 03-26-2010, 08:59 AM   #8
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Re: OBD-II never comes up ready - HELP!

Thank You God! I finally got the truck through inspection!

Primary solution was simply replacing the thermostat. This allowed the engine to run closed loop. This allowed the ECU to collect data during the drive cycle to prepare readiness tests.

But, my truck never fully came ready. The Evaporative System never came up ready. And, when I got inspected, the EGR System not was ready either. I scanned the engine and monitored readiness tests just before taking it in.

I learned how to interpret the test results to determine why a test might not be ready (not all tests completed Pass):
http://service.gm.com/gmspo/mode6/

...that's a very cool site setup by GM for mechanics. You can get OBDMID test details and you can also get Trouble Code details. Very cool.

But, I also learned that the EPA allows vehicles year 2000 and below to go through even with two of the whatever: 8-11 readiness tests not ready. Check that out here:
http://www.obdii.com/articles/OBDII_...s_Testing.html

...this is a great article. Scroll down to the section on READINESS FLAGS and you'll see that up to 2 tests can be down. 2001 and above must have all but one test ready to get through.

So, now that I'm though inspection - I could not possibly care less as to why the EVAP system won't come up. ...at least not for another 2 years ;-)

Last edited by blairwag; 03-26-2010 at 09:07 AM.
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