1999 California Yukon 5.7 V8 fails smog in Mexico

Maintenance/Repairs
1

Here in Mexico again. Cousin’s 1999 Yukon, 5.7 V8, imported from California. The transfer paperwork said 105,000 miles so I am guessing it has 120,000 or more on it.

It recently failed smog verification, and the smog booth told them it had a bad sensor. They did not say which one, except the “gas sensor”.

The problem is, it has 4 sensors, as best as I can tell. Two before cat converters, and two after. Sensors cost even more in Mexico than in the US, and I wanted to be sure if possible before buying sensors. And, at this time I am not even sure the sensors are bad. So, if I can come up with no better information, he may be forking out a weeks pay as a wild guess…

I took my Equus 3140 scanner, with live data and hooked it up. No driving, just started motor and started reading live data while it warmed up. Everything seemed to be correct, though I think I will look at it again tomorrow to see if maybe I missed anything, such as all readiness.

No codes found. I got the green light.

I did record all live data, but think putting them all here would be excessive. Temps looked correct. I noticed it said AIR OFF.

STFT B1 -2.3%
LTFT B1 -6.2%
STFT B2 -3.1%
LTFT B2 -3.1%

O2s B1 S1 (v) bounced around ended up .840
O2s B1 S2 (v) .755
O2s B2 S1 (v) .805
O2s B2 S2 (v) .735

Live sensor test:

O2S B1 S1 0.480 no spec listed
O2S B1 S2 NO TEST
O2S B2 S1 0.480 no spec listed
O2S B2 S2 NO TEST

My 2002 Toyota Sienna California heated sensors have totally different values. Like 3.4.

LOOKS LIKE ONE NON CONTINUOUS FAILED!
Non continuous test

Test ID $07
Module# $10
Component ID $0C
Min N/A
Max $0000
Test Value (HIGH) $dc00

Tests $0C; $03; $06 in spec. Only $07 fails. As you may suspect I have no idea what it is testing.

I have Googled until I almost fell off my chair, and can find no explanation for GM non-continuous tests, except pay boards.

The best I could come up with was a PDF file which said non-continuous tests tended to usually include: Evap; EGR; Catalytic Converter; Air; and O2 Sensor, though it implied some cars may have more. Clearly, some of these could cause a smog test fail.

I do not want to run EVAP test because it says I must see the service manual to see how to stop it. Sigh.

Thanks for any tips or help on this.

AFTERTHOUGHT: I think tomorrow I will go back, and assuming it has a PCV valve, check that sucker. I don’t think they are heavy on maintenance, though I have got them to changing transmission fluid and antifreeze.

2

From your assessment of the mileage it does not sound like the truck gets driven much. My similarly low mileage Suburban (94) failed the emissions test a few years ago due to dirt in the EGR passage in the intake manifold. I had this cleaned out and now try to get in some sustained high speed highway miles at least once every four to six weeks. I’m scheduled for another test next year and having already replaced plugs,ignition wires EGR (due to stored code) and PCV this past summer (and cleaned the distributor cap and rotor) I intend to replace the cap and rotor, clean my K&N air filter and take the truck out for an ‘Italian’ tune-up on the day of the test. Of everything I’ve done to self tune I have to say that cleaning the distributor cap (or replacing it) has made the most noticeable difference in performance. There’s a good steep rail overpass near where I live and I know I’ve got it right when she accelerates nice and smooth all the way to the top without requiring a lead boot on the gas.

3

Non-continuous refers to tests that occur at specific points in the operational cycle but are not being done continuously (hence the name ;). These are most often associated with the readiness monitors like EVAP for example.

How can they only say it failed for a “gas sensor” and leave it at that? Don’t they have to provide specific codes or protocols for reference? Or is this just the owner’s interpretation of the failure that was reported to them?

4

Check this reference out- http://www1.snapon.com/Files/Diagnostics/UserManuals/GlobalOBDVehicleCommunicationSoftwareManual_EAZ0025B43B.pdf

$07 is a check for pending codes (see page 17 in the link). Codes that have not yet met the criteria for setting the CEL but have been detected during the last drive cycle.

5

Me thinks someone was looking for a little payout here.

6

Keith, actually what you say is relevant. Normally, when they have the Yukon verified, the person at the booth says it fails, but if you pay him roughly $30, he says, okay, it passed.

In this case, he refused to take the money, and told them it had to be fixed. My conclusion is, he doesn’t take money to pass failed smog. He lies and says it failed when it didn’t, for money. So, he takes money to pass a passed smog test.

In this case, he wouldn’t take the money. An interesting development.

More later, it got late on me. Thanks.

7

Guys, check this out. No more guesswork, at least as to what "failed"
Maybe this’ll help
This doesn’t necessarily explain the oxygen sensors which are supposedly faulty.
“no EGR off-idle test”
“MAF out of range high”

http://service.gm.com/gmspo/mode6/pdf/GM%20Class2%20mode%20$06%20data%20final_dm.pdf

8

db4690, makes sense to me. TwinTurbo’s advice, I spent a lot of time on that reference, and I don’t think his is the same thing. Service numbers seem to be only a part of the software, as opposed to a test number of non-continuous tests.

But, this one does look right! We need to store this great resource as well as the GM index:

http://service.gm.com/gmspo/mode6/ and possibly others. This is good stuff, and my Google work found none of it! Great job!

Let me digress here. My opinion is that verbal statement that the sensors were bad was an off the cuff comment and I was not convinced, which is why I was asking here what this all meant. I don’t think the smog verification crew are trained master mechanics, and my guess is they are so used to bad sensors they assume that is the problem.

Remember, I am in a place where even Autozone does not usually have 5W30 oil. A parts place tried to tell me I didn’t want 5W30 because it would not protect my engine. They sold only 20W50, seriously. So, one does not always encounter high tech.

MAF on the live data said 0.9 lb/minutes.

I need to do some more Googling, and I have a lot of hits on the message definition. Big question is why no code set. Also what could cause this failure. Based on the number of hits on “No EGR off-idle test MAF out of range high” I suspect with elbow grease I will get some answers on Google. Thanks, I will keep y’all posted.

I am storing as much of this as I can. They drive cars here a long time, and my guess is, this will not be the last problem that 1999 Yukon has.

9

I found the following on http://obdcon.sourceforge.net/2010/06/interpreting-generic-obd-ii-scan-data/ but do not have a graphing scanner.

“The process for testing the sensors is simple: The sensor needs to exceed .8 volt and drop below .2 volt, and the transition from low to high and high to low should be quick.”

Mine simply reported 0.480 when idle after warm-up.

I may keep posting details here in hopes it will be useful to others with similar problems. There is more involved then reading codes, it seems.

10

Do you have any idea how fast your scanner “refreshes”?
Perhaps you can backprobe the appropriate connectors with a multimeter. My Fluke 88 has a min/max function. You set it up to “record.” Then afterwards, it gives you the minimum, maximum and average readings.
Your Toyota Sienna most likely uses A/F air fuel ratio sensors, which have totally different values, as you already discovered.

11

So far I have found several forums with this exact question, (Maf out of range high, no EGR off idle test) as old as 4 years. And, no one has ever answered it.

12

What is your idle like?
Pretty smooth, with no intermittent fluctuations?
Perhaps you intermittently have EGR when you don’t need it . . .
Perhaps your EGR valve is partially open
What kind of MAF readings are you getting?
At idle and when you stomp on the throttle?

13

I would want to look at the O2 sensors directly with a scope to see if the fronts are switching properly and the rears are more steady.

You might consider investing in something like THIS.

14

Sigh! I told you they are not very technical here. It finally occurred to me to ask if they were given a paper rejection. Yep. And, when they let me see it, it said as best as I can translate, “Did not perform test due to visible smoke.”

I sent a message to the son-owner in Chicago telling him to forget about sensors. This car needs mechanical work. Sensors almost certainly do not cause visible smoke. I am not even sure the verification crew told them to replace sensors.

Oil burning might cause visible smoke. Antifreeze in the cylinders might. But, as far as I can tell sensors most likely do not.

I do not understand why no codes set at all. Much oil smoke should destroy the cat, no?

And, I also do not understand why the sensors read the same. It seems on my Sienna the sensors before and after cat were the same cold, and as the cat started burning gases, the last sensor dropped way down.

Since I learned a lot, though not enough, and there may be others who are curious about strange failures, such as the non-continuous failure, I think I am going on with the technical stuff. Those not interested, feel free to hit BACK.

http://service.gm.com/gmspo/mode6/pdf/GM%20Class2%20mode%20$06%20data%20final_dm.pdf 16 page PDF file.

Test $03 seems to be Secondary Air injection tests on GM. Page 2 of 16.

Test $06 seems to be O2 Sensor time to activity. Page 6 of 16.

Test $OC seems to be Catalyst Efficiency Monitor. Page 8 of 16.

Test $07 is the failed test, pages 6 and 7 of 16. Test $07, when performed, seems to test the EGR function. The component numbers tend to be for reporting various results of the test. Component 0C, I think, reports that the test was not performed, and the reason why it was not. There are other components for other things, including actual failures.

An EGR takes relatively cool exhaust gases, mostly CO, and feeds it into the intake. If combustion temps reach 2500 degrees, NOX is produced. At idle, EGR should not feed in exhaust, because temps will not be that hot. And, at Wide open throttle, it does not, because the same gases which cool combustion also reduce engine performance.

Exactly what the off-idle test does, I am not sure. One writer said the computer changes the EGR setting, then measures to see if an expected change occurs.

In any case, GM has a table of conditions and criteria for different GM OBDII tests.

http://service.gm.com/gmspo/mode6/pdf/1999/99c57G_F__yE.pdf is a 25 page PDF file. There are several EGR tests, but the most complicated one, EGR FLOW LOW, is on page 13 of 25. This chart is for 1999 5.7L (LS1) F-car ENGINE DIAGNOSTIC PARAMETERS. I picked the only 5.7 not for trucks. Or, is Yukon a heavy truck?

Criteria is: “Actual delta MAP change is less than a table lookup delta MAP change as a
function of an EGR valve commanded position during a decel.”

This is a 2 second test, and the chart lists the CEL warning mode for failure. Also, this one is run once per trip.

But, this test, as in many of the tests, is performed only when certain conditions are met. Here is the condition list for that EGR FLOW LOW test. I am not sure this is the one which fails, but it is the only EGR test listed. [] indicates my notes.

No TP DTCs set
No MAP DTCs set
No VSS DTCs set
No ECT DTCs set
No IAT DTCs set
No EGR Pintle DTCs set
No System voltage DTCs set
ECT between 60 Deg C and 117 Deg C [Coolant temp]
IAT < 65 Deg C [Intake air temp]
System voltage between 11.7 volts and 18 volts
Vehicle speed between 26 MPH and 70 MPH [car must be moving]
RPM between 800 RPM and 2000 RPM

IAC not moving more than 5 steps [on this test, it seems that it may change EGR and notes how much IAC has to move to compensate.]

Engine vacuum between 83 kpa and 60 kpa
BARO > 70 kpa [not sure what that is at 6,000 feet up]
MAP not changing more than .5 kpa
TP < 1.1% [I think TP is throtle position}
VSS change < 4 MPH
Not in DFCO

If the failed noncontinous test is not the same, the same sort of complex conditions will apply.

In any case, for some reason the computer did not run the relevant EGR test, because MAF was out of desired range, whatever that means. Yeah, I know what MAF means, but no idea what MAF is doing for this test, nor why, nor what the desired range is.

And, my theory is there is no code set, because the test is not run, thus no failure to report.

I think some idea of what is involved in other tests can be derived by the same technique. Anyway, as little as I know, it is much more than a few days ago.

15

Yes, circuitsmith, that pocket scope would be nice!

I don’t do ebay, but my SIL does.

Db, I cannot answer your questions at this time. I need to look at them, but due to discovery of total bust on the claim that sensors need replacing am backing off on this now. Thanks.