GM Oil Life Sensor Troubleshooting

Under ideal conditions the oil life may not come on for up to a year and/or

Have done that Shep.

I was talking to someone with similar engine and driving style/climate etc. and his came on between 8,000 to 12,000 kms.

A lot of sites claim that 7500 miles is programmed as the upper limit.

I've done oil changes without resetting the light and it still hasn't stayed on.

I was just wondering if there is a procedure to check it out.

My wife's Buick has one of these idiot lights, and I have never researched the way it functions. Consequently, I ignore it, and change oil on schedule.

Can any of the pro's on here give a quick discussion of the theory behind the oil change lights? Much appreciated.

One thing I can touch on and clear up.....the GM oil life monitor operation and my statement that ZDP (or ZDDP as you tend to call it here...most of the API literature just sticks to ZDP so I tend to use that) depletion is the basis for oil deterioration.

My spelling is poor but ZDP stands for zinc dialkyldithiophosphate which , as it sounds, is an anti-wear compound comprised of zinc and phosphorus.

ZDP is dispersed in the oil so as to be at a potential wear site if a surface asperity happens to break thru the oil film thickness causing the dreaded metal-to-metal contact. A molecule of ZDP must be present at that moment to prevent microwelding at the contact site which will cause material transfer, scuffing, scoring, wear and catostrophic failure. The concentration of ZDP in the oil will determine if there is ZDP present to work it's magic. The greater the concentration...the more likely a molecule of ZDP will be there...and vice versa.

By nature, ZDP is sacrifical. As ZDP is "used up" at a wear site to prevent micorwelding the concentration of ZDP decreases.... So...if you measure the ZDP concentration in engine oil in a running engine it will decrease at linear rate based on engine revolutions. Any given engine has a certain number of high potential wear areas where metal- to-metal contact could occur due to reduced film thickness and/or surface asperities....areas such as rubbing element cam followers, distributor gears, rocker arm pivots, push rod tips, etc...... The more of these areas the more ZDP depletion. The more often these features come in contact the greater the ZDP depletion. That is why, generally speaking, ZDP concentration in the oil, for any given engine, will decrease at a fairly linear rate when plotted versus cummulative engine revolutions. The more times it turns the more contact the more chance for wear the greater the depletion. This is as much of a fact as I could quote ever and is really not speculation or anything. It is proven beyond a shadow of a doubt in many studies. That is why it is ONE of the basis for determining oil life remaining and why it is THE basic premis of the GM oil life algorithm. It is only ONE of the things that determines oil life...but it is the one thing that can be tied to engine operation in a linear fashion and estimated very accurately by accumulating engine revolutions via a counter.

The GM engine oil life monitor counts engine revolutions and accumulates the number for the basis of the oil life calculation. It then adds deterioration factors for operating temperature, start up temperature, soak times, ambient, coolant temperature, etc... There are a LOT of factors that "adjust" or affect the slope of the deterioration but the fundamental deterioration is traced back to the ZDP depletion that is inescapable with engine revolutions. The specific rate of ZDP depletion is readily measurable for any given engine so that is the fundamental item that is first calibrated for the oil life algorithm to tailor it specifically to that engine.

You would obviously like to get the oil out of the engine before the ZDP concentration gets so low that it is ineffective at being at the right place at the right time and preventing engine wear so that becomes the long term limit on oil life for that application.

The other things that determine oil life such a acid build up, oxidation, petane insuluables such as silicon from dust/dirt, carbon or soot build up from the EGR in blowby, water contamination, fuel contamination, etc.... are all modeled by the multipliers or deterioration factors that "adjust" the immediate slope of the line defined by the engine revolution counter as those items can be modeled in other ways and accounted for in the immediate slope of the ZDP depletion line.

The algorithm was developed over the course of many years by several lubrication experts at GM Fuels and Lubes, spearheaded by Doctor Shirley Schwartz who holds the patents (with GM) for the algorithm and the oil life montitor. I had the luck of working directly with Dr. Schwartz when the idea of the oil life monitor first progressed from the theoretical/lab stage to real world testing/development/ validation. There were fleets of cars operated under all conditions that deteriorate the oil life for any and every reason and , thru oil sampling and detailed analysis of the oil condition, the algorithm was developed, fine tuned and validated to be the most accurate way invented yet to recommend an oil change interval by. As just one example, I have seen cars driven side-by-side on trips, one towing a trailer and one not, for instance, to prove the effectiveness of the oil life monitor in deteriorating the oil at a faster rate just because of the higher load, higher average RPM, higher temps, etc...and it works flawlessly.

The oil life monitor is so effective because: it is customized for that specific vehicle/engine, it takes everything into account that deteriorates the oil, it is ALWAYS working so as to take into account THAT INDIVIDUALS driving schedule, and it tailors the oil change to that schedule and predicts, on an ongoing basis, the oil life remaining so that that specific individual can plan an oil change accordingly. No other system can do this that effectively.

One thing is that I know personally from years of testing and thousands of oil analysis that the oil life algorithm works. There is simply no argument to the contrary. If you don't believe me, fine, but, trust me, it works. It is accurate because it has been calibrated for each specific engine it is installed on and there is considerable testing and validation of the oil life monitor on that specific application. NOt something that oil companies or Amsoil do. They generalize....the oil life monitor is very specific for that application.

Oil condition sensors in some BMW and Mercedes products are useful, also. They have their limitations, though, as they can be blind to some contaminates and can, themselves, be contaminated by certain markers or constituents of certain engine oils. Oil condition sensors can only react to the specific oil at that moment and they add complexity, cost and another potential item to fail. One other beauty of the GM oil life monitor is that it is all software and does not add any mechanical complexity, mass, wiring or potential failure mechanism.

There is considerable safety factor in the GM oil life monitor. Typically, I would say, there is a 2:1 safety factor in the slope of the ZDP depletion curve....in other words, zero percent oil life per the ZDP depletion is not zero ZDP but twice the concentration of ZDP considered critical for THAT engine to operate under all conditions reliably with no wear. This is always a subject of discussion as to just how low do you want the ZDP to get before the oil is "worn out" if this is the deciding factor for oil life. We would tend to be on the conservative side. If the oil life is counting down on a slope that would recommend a 10K change interval then there is probably 20K oil life before the ZDP is catostrophically depleted....not that you would want to go there...but reason why many people are successful in running those change intervals.

Please...NOT ALL ENGINES ARE THE SAME. The example above is an excellent practical justification of why you would want to add EOS and change the 15W40 Delvac in the muscle car at 3000 miles max and yet can run the Northstar to 12500 easily on conventional oil. You must treat each engine and situation differently and what applies to one does not retroactively apply to others. This is where Amsoil falls short in my book by proposing long change intervals in most everything if you use their oil. It just doesn't work that way. You can run the Amsoil to 12500 with no concerns whatsoever in the late model Northstar because even the oil life monitor tells you that for conventional oil off the shelf. Would I do that to the 502 in my 66 Chevelle...NO WAY. Amsoil says I can though. Wrong.

There are entire SAE papers written on the GM oil life monitor and one could write a book on it so it is hard to touch on all aspects of it in a single post. Hopefully we hit the high spots. Realize that a GREAT deal of time, work and energy went into developing the oil life monitor and it has received acclaim from engineering organizations, petroleum organizations, environmental groups all across the board. It is not some widget invented in a week and tacked onto the car.

The oil life monitor is not under the control of a summer intern at GM Powertrain per an earlier post....LOL Not that a summer intern wasn't compiling calibrations or doing a project on it but is under control of the lube group with a variety of engineers directly responsible that have immediate responsibility for the different engine families and engine groups. The idea that a summer intern was responsible for or handling the oil life monitor is ludicrous.....LOL LOL LOL

The following is the response of a GM engine development engineer to a motorcycle forum on extended mileage oil changes. The link to the forum was posted on VV months ago. I found it so interesting I saved a copy. Read with an open mind and form your own opinion about your favorite oil and oil change habits. Only the GM engineer's responses to questions, converted to plain text format, are included. The GM engineers experience and credentials are in the first few sentences of the last paragraph. It's taken special handling to get this long message posted, thanks to vv-help. I've got the entire original in pdf format for those interested...

Animation from GM,

Hey regulars....read this guys posts. You are getting the real story about oil changes here.

Good stuff!

Ian

Thank you Ian.

Is there a way to check the system out besides the bulb check?

Thanks for your tutorial on changing out the intake gasket on the

It really helped!

You know what? I'm not aware of anyone ever complaining about the operation of the oil life monitor at our dealership. So as a result, the idea of checking the system has never crossed my plate. I'll have to check into it.

Hey, no problem. I'm glad it was helpful.

Ian

Thanks for taking the time to explain all of this. Following the indicator can save a lot of wasted money on the 3000 miles changes some people use because the oil change place tell them that.

Good reading. Thanks for posting it.

John

I appreciate your post. I had no idea that they had put so much effort into this system. My "idiot light" comment was an assumption and is apparently unfounded.

One more question: Several have posted that they have not seen many incidences of the system being suspected of not working. But I would also assume that, if one nears the oil change interval recommended in the manual and if the system warning doe not trigger, one should consider the time or mileage interval to override the warning light??

Very interesting post.

If there is an engine failure within in GM's warranty period, do they ever ask for verification of oil changes in a timely manner? Timely manner being the interval listed in the owners manual.

Thanks

GM says in their owners manuals to change the oil and filter within at least a year, no matter what the oil change monitor says. They also say that if you are unable to determine if the oil life monitor is either working, or was reset inadvertantly between oil changes, to revert back to the 3000 mile oil change interval, then confirm that the monitor is reset after that oil change.

Ian

Many thanks, Ian.. There is not a GM in our immediate future, but wife's car has this monitor. At this stage of mileage, warranty is not an issue/

We pick up our new car on Friday.

By the way, one heck of a competition in Malaysia! Kudos to Team McClaren.

It depends. If nothing really stands out to the tech when tearing the engine down, then it just gets repaired. If the engine is seized, and when we drain the oil, all that comes out is jelly, then yes, they may ask for maintenance records.

Ian

This gelled oil problem stands out as a problem for a number of manufacturers.

Paraffinic oils do not normally gel under heat alone. The additives can "go south" but the basic oil molecules are relatively stable. They can gel if water is incorporated into the equation, or if polymerization occurs *, or if additives give up the ghost, or if crosslinking via salts occurs.

Synthetics are not necessarily immune to this either.

If oxygen (read it the same as "air") gets into hydrocarbons or synthetic esters, and heating is applied, then the whole chemistry changes. Acid numbers decrease, often. Viscosity increases. Density increases. Color goes to brown or black. (This phenomenon, plus the decomposition of additives, are the main two causes of varnishing of engine parts IMO.)

If an engine has small oil passages, the problem is aggravated.

I tend to think that the real problem with gelled or sludged oil is well defined, but that the ultimate repositories of this knowledge are protecting the information.

IF you abuse your car, then - I agree - you have no comeback. If however the conditions of design and operation are such that failures occur suddenly and without warning, then the manufacturer needs to belly up to the apology counter.

Maybe someday we will know the facts in these cases.