LLY Duramax Low Oil Pressure

[Jorgy]

Been looking at forums all morning trying to pinpoint what the exact issue is. Symptom is the pressure gauge jumping back and forth erotically and when come to a stop (once vehicle is warmed up) it will show low oil pressure in the DIC and gauge. As soon as I accelerate it goes away. Last year I replaced the oil pressure sending unit in the block and appeared to solve the problem, except it would come on when stopped once in a while. Did some research which showed it’s the stepper motor so I continued to run it this year after working all summer. Ran it 10,000km this year with no issues until this morning when going to take for an oil change. Washed the truck at the car wash and sprayed under the hood. Stated the truck up and the light was on all the way to get an oil change.

I stopped at CT and bought a can of sea foam and put it in the oil tank to maybe clear up any blockage, seemed to maybe help, but tough to tell. Changed oil and still going off as I parked in garage. The gauge jumps around at idle or even steady throttle, which makes me believe it is a bad ground on the unit. Any idea where to look for this bad ground?

 

[Legend14]

Do you get any DTC codes? If not probably a bad stepper motor in cluster.

 

[sirkdev]

Tex78 is your guy..

 

[brian h]

Instrument cluster is common. Why not put a pressure gauge on and see what oil pressure is?

 

[1200]

I wouldn't trust the cluster. I would check it off the motor i bet its fine .

 

[JMCX]

Get a test gauge on there to see what's really going on.

 

[ABMax24]

My bet is on a bad wiring/wiring harness to the sender, LLY's are known for having electrical issues. Otherwise it could be a bad sensor.

It isn't a bad stepper motor, a bad stepper motor won't trigger the low oil pressure light, these are 2 independent functions controlled by the ECM. The only reason it shows low oil pressure on the gauge and the warning light is because the ECM is actually seeing a low pressure signal.

If it's none of these options it's actually low oil pressure, IIRC the motor needs to be pulled to replace the oil pump.


Best diagnostic test is a to hook up a mechanical gauge, if the mechanical gauge reads normal oil pressure it's electrical, if not you're pulling the motor...

 

[Jorgy]

Do you get any DTC codes? If not probably a bad stepper motor in cluster.

No DTC codes on my reader/tuner

 

[Jorgy]

Instrument cluster is common. Why not put a pressure gauge on and see what oil pressure is?

I would have to track one down, I don’t have access to a pressure gauge for this application yet!

 

[Jorgy]

My bet is on a bad wiring/wiring harness to the sender, LLY's are known for having electrical issues. Otherwise it could be a bad sensor.

It isn't a bad stepper motor, a bad stepper motor won't trigger the low oil pressure light, these are 2 independent functions controlled by the ECM. The only reason it shows low oil pressure on the gauge and the warning light is because the ECM is actually seeing a low pressure signal.

If it's none of these options it's actually low oil pressure, IIRC the motor needs to be pulled to replace the oil pump.


Best diagnostic test is a to hook up a mechanical gauge, if the mechanical gauge reads normal oil pressure it's electrical, if not you're pulling the motor...

Through lots of forum reading today I found this to be very common. Check the electrical shorts, grounds, clean all connections first to check that off the list. I did that today and replaced the pressure switch/sending unit last year. The craziness of the gauge is what’s tells me it’s electrical, otherwise how would the oil pump work so intermittently

 

[rsaint]

I have a LLY and it will be your cluster went thru same crap with temp gauge changed tstats and same reading found a rebuilt cluster and all good now. Truck is a 05 gmc.

 

[Legend14]

You can get the stepper motors off eBay but my sodering skills suck so I got the guy on Kijiji to fix it. You can still drive without cluster too if you need to

 

[Jorgy]

You can get the stepper motors off eBay but my sodering skills suck so I got the guy on Kijiji to fix it. You can still drive without cluster too if you need to

I watched YouTube videos on soldering to replace the stepper, it doesn’t look too bad but also a lot of things to take apart and carefully put back together. Would prefer to do a whole new cluster once something else fails, if that’s the issue

 

[kenvb]

im retired licenced mechanic.but a old school mechanic.dont know or want to know much about computorized vehicles.i would put a mechanical gauge in the truck.under dash or somewhere.

 

[MK4TDI]

No DTC codes on my reader/tuner

Can you plug your tuner into a computer ?

If so you might be able to see what the sensor is seeing.

Or perhaps your tuner can see what oil pressure the ECM is seeing.

 

[tex78]

Been looking at forums all morning trying to pinpoint what the exact issue is. Symptom is the pressure gauge jumping back and forth erotically and when come to a stop (once vehicle is warmed up) it will show low oil pressure in the DIC and gauge. As soon as I accelerate it goes away. Last year I replaced the oil pressure sending unit in the block and appeared to solve the problem, except it would come on when stopped once in a while. Did some research which showed it’s the stepper motor so I continued to run it this year after working all summer. Ran it 10,000km this year with no issues until this morning when going to take for an oil change. Washed the truck at the car wash and sprayed under the hood. Stated the truck up and the light was on all the way to get an oil change.

I stopped at CT and bought a can of sea foam and put it in the oil tank to maybe clear up any blockage, seemed to maybe help, but tough to tell. Changed oil and still going off as I parked in garage. The gauge jumps around at idle or even steady throttle, which makes me believe it is a bad ground on the unit. Any idea where to look for this bad ground?

99% it's the cluster

Would have to either do a manual oil psi test, or watch live oil psi data to confirm

 

[Cableguy]

tex would a edge cts 3 give accurate oil pressure my dash is always low on idle but fine when driving

 

[tex78]

tex would a edge cts 3 give accurate oil pressure my dash is always low on idle but fine when driving

Just looking for the live eop sensor data


Now you mean low, so less than 1/4 on the gauge right

You realize that 200 kpa or the 1/4 tick, is 30 psi oil psi, and is a normal thing

 

[Jorgy]

99% it's the cluster

Would have to either do a manual oil psi test, or watch live oil psi data to confirm

How would I go about a manual test, where does it get hooked up? Type of gauge and where to buy?

The weirdest thing is it’s been fine all winter, I go one day to the car wash and actually spray underneath the hood, comes on immediately...

 

[Jorgy]

Can you plug your tuner into a computer ?

If so you might be able to see what the sensor is seeing.

Or perhaps your tuner can see what oil pressure the ECM is seeing.

I can’t plug my tuner in, it’s an older style Hypertech. I’ll look and double check. I’ve been considering a cts tuning and doing EFI live which would show it