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.

 

Your Coolant Temperature Sensor CIRCUIT needs butter, cause it's



I think it is not telling the computer to go from Open Loop (cold motor), to Closed Loop (warmed-up motor). So the ECM doesn't take readings, and nothing is ready (to take readings).

Only thing I can think of here... (thinkin' too much hurts the brain too )

 

everytime you shut off the motor the ecm resets....when you turn it back on it runs thru a series of self tests to check its systems.......it should give you a code after it has run thru the tests with the key on but motor off.

 

I agree with Schrade. Had the same problem with my 2000, I had no SES light & no codes but failed inspection due to OBD-II readiness. Shop owner suggested it was a temp problem & to check the thermostat & coolant temp sensor. Replaced sensor & the problem was solved.

 

Humm. Temp sensor. Now, THAT would be cool.
OK, 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 ****.

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.

Oh, and BTW, thanks - everyone. you've already been tremendously helpful. I can't express in words how much I appreciate it. :-)

 

Notice CLOSELY the 5th word, in capital letters, in my other post.

Even then, what I said is not definitive, it is something to THOROUGHLY check.

 

I understand what you're saying. Check the Coolant Temperature Sensor Circuit.
But, in researching, I've gleaned two concerns/considerations:
1) Many folks mix Coolant Temperature Sensor with Temperature Switch.
......in all my reading, I don't know which is which, 'cause so many people have used the terms to describe both sending units.
2) It is often easier and cheaper to replace such a sending unit than it is to accurately test it. And, since I'm just a basic DIY garage hack, I think I'd rather replace than screw around with my digital multi-meter, fumbling around the hot engine.

I know it's not perfect, but that's kind of how I do things.

I also understand this this is not definitely my problem. And, yeah, sure, testing the circuit thoroughly is probably a better approach. But, I don't know how to test it, not sure what the correct readings should be, and I'm optimistic I'll get lucky and replace a few parts and then the world will be a better place. Know what I mean ;-)

I could really use a good source to distinguish between the CTS and the Temp Switch, with an indication of where the temp switch is located on my '97 4.3.

I definitely plan to swap out the thermostat. Seems like I should have done that some time ago, anyway.

Thanks again. Not only for your help, but for your patience with me, too. TIA :-)

 

The sensor for the gauge is in the cylinder head between cylinders 3 & 5. The sensor for the PCM is in the intake near the thermostat. You should be able to monitor the PCM sensor with your scan tool. I think I posted resistance values for the gauge sensor in the past.

 

If you don't like using the multimeter, you can use the old fallback analog multimeter, uses pain as the indicator of current. Advanced model has volume meter for scream.

 

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

First off - thanks to everyone so far, for helping. You guys are great!

OK, 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 using swartlk's procedure. Very easy, just a little time consuming. 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 (argh!):

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 again everyone, and I'll keep ya posted!