[Taxman]

So if I subscribe to GDS and flash my 2016 and 2017, will they start running 5th down the freeway in the winter on humid days?

 

[Barry Allen]

So if I subscribe to GDS and flash my 2016 and 2017, will they start running 5th down the freeway in the winter on humid days?

I had wondered about that, and it's certainly possible. From the TSB, this appears to be something added to the gasoline engines for model years 2018-2019. It would not surprise me if a couple lines of code were added to updated versions for ECUs in 2016-2017 model years and it gets loaded on there if you flash to the latest version.

 

[Barry Allen]

So if I subscribe to GDS and flash my 2016 and 2017, will they start running 5th down the freeway in the winter on humid days?

Though, now I'm second-guessing that. The TSB references only model years 2018-2019, and if GM were to add that code to ECU updates for 2016-2017 model years it would create a nightmare where a tech might be trying to diagnose a problem that the TSB doesn't reference for that model year. GM would have to update the TSB to specify this is added to prior model year vehicles if the ECU is updated to or past a certain version of firmware, and then technicians would have to take the step of checking the ECU firmware to determine if it was added to a prior model year vehicle.

Maybe GM leaves it out of the updates and all the owners of 2016-2017 Cruze vehicles just have to deal with water condensing and freezing in the intake.

 

[Ma v e n]

So if I subscribe to GDS and flash my 2016 and 2017, will they start running 5th down the freeway in the winter on humid days?

My guess is no. Just like an ECM flash doesn't change your autostop temperatures to 18-19 spec.

 

[Eric.landwehr]

I have a 2019 and notied my fuel MPG dropped a lot.. Then i noticed it is not shifting to 6th. But if i drive 80 mph the 6th gear kicks in.. But below 80 mph it drops to 5th. I have lower rpm above 80 then 65..
And yes its about 20°F here. But after and hour of driving it should be hot..

Also if i manually shift it still does not shift to 6th.. Frustrated now

 

[Barry Allen]

But after and hour of driving it should be hot..

This is nothing to do with the temperature of the engine. It's 100% the temperature and humidity of the ambient air.

 

[Eric.landwehr]

This is nothing to do with the temperature of the engine. It's 100% the temperature and humidity of the ambient air.

Thanks..anything i can do before spend money and going to the dealer?

 

[Ma v e n]

I have a 2019 and notied my fuel MPG dropped a lot.. Then i noticed it is not shifting to 6th. But if i drive 80 mph the 6th gear kicks in.. But below 80 mph it drops to 5th. I have lower rpm above 80 then 65..
And yes its about 20°F here. But after and hour of driving it should be hot..

Also if i manually shift it still does not shift to 6th.. Frustrated now

This is normal operation. If it's below 30F my car will shift from 6th to 5th after probably a half hour of 50-60mph driving. And won't shift to 6th again during that trip (I don't exceed 70mph typically) this happens everyday on my commute to work (64miles) no trouble codes, no indicators. As mentioned multiple times, there's a TSB (18NA035) that addresses this

 

[Ma v e n]

Thanks..anything i can do before spend money and going to the dealer?

Yeah, you can stop worrying about 8t LOL.

Or you can go annoy your dealer and spend money to attempt to fix a design feature

 

[Eric.landwehr]

This is normal operation. If it's below 30F my car will shift from 6th to 5th after probably a half hour of 50-60mph driving. And won't shift to 6th again during that trip (I don't exceed 70mph typically) this happens everyday on my commute to work (64miles) no trouble codes, no indicators. As mentioned multiple times, there's a TSB (18NA035) that addresses this

Thanks I just read the TSB.. I feel better that its nothing major.. Thanks again

 

[Ma v e n]

It's not only "nothing major" it's normal operation.

 

[Barry Allen]

But if i drive 80 mph the 6th gear kicks in.. But below 80 mph it drops to 5th. I have lower rpm above 80 then 65..

I do not know what sensors exist for the ECU to sense humidity in the ambient air, but certainly there are one or more temperature sensors in different points of the air intake system.

If you have air containing high humidity and the temperature is below freezing, you can end up with that moisture in the air freezing up in the intercooler. The air will go through the turbocharger and if it's not compressed to a high enough pressure, it is possible for the air to flow through the intercooler and be chilled to a point where the moisture freezes inside the intercooler. This is obviously a problem.

The solution is to have the ECU operate the engine as best as it can to make sure the temperature of the air going through the intercooler is kept above freezing if there is lots of moisture in the air. This can be done by keeping boost pressure high enough, so the ECU drops down a gear to make sure this happens.

 

[Eric.landwehr]

Wow.. Thank you for clearing that up.. great explanation..

 

[Ma v e n]

The "MAF" sensor on these cars is actually a multifunction air intake sensor. It integrates a humidity sensor.

 

[Barry Allen]

The alternative could be to block off the intercooler in cold weather. Like the semi tractors and school buses that have a "winter front" on the grill to stop or reduce airflow through the radiators in cold weather, this might keep air flowing through the intake above freezing and the ECU might then allow 6th gear to be used.

But this sounds like a lot of work to find something that you can get under the car and zip-tie to the intercooler.

 

[TDCruze]

Guess this is only in the gas models. The 9 spd holds 8 for a bit when very cold, then always goes to 9th and never looks back. Doesn't matter how cold the ambient temperature is.

Making a winter front on the grill may be worth a try to prevent this shift issue. It definitely helps the engine warm up faster in very cold weather.

 

[Barry Allen]

Guess this is only in the gas models. The 9 spd holds 8 for a bit when very cold, then always goes to 9th and never looks back. Doesn't matter how cold the ambient temperature is.

It's possible the Diesel models use the variable vanes on the turbo to run higher boost levels, keeping the air flowing through the intercooler above freezing. Diesel engines can run higher amounts of air and keep the same amount of fueling because they always run lean. I have no knowledge this is what happens, but it's possible.

 

[TDCruze]

It's possible the Diesel models use the variable vanes on the turbo to run higher boost levels, keeping the air flowing through the intercooler above freezing. Diesel engines can run higher amounts of air and keep the same amount of fueling because they always run lean. I have no knowledge this is what happens, but it's possible.

Very true that is possible. I will have to watch the boost on a cold startup drive.

 

[Ma v e n]

I don't know if a grille cover will resolve the issue, as I don't believe it takes post cooled air temp into account, only ambient, intake and humidity.

 

[Barry Allen]

Very true that is possible. I will have to watch the boost on a cold startup drive.

Not must a cold startup drive. It's a drive at highway speeds through climate that is both below freezing (so maybe high 20s F) AND has high humidity. We get that a lot around here: Foggy winter days.