SSM 49811 - A/C inoperative - Heater Inoperative - Ambient Temperature Reads -4 Degrees

[breeves002]

SSM 49811 - 2021 Mustang Mach-E - 21 May 2021 - A/C inoperative - Heater Inoperative - Ambient Temperature Reads -4 Degrees

Some 2021 Mustang Mach-E vehicles may exhibit a concern of the air conditioning(A/C) and heater being inoperative with the ambient temperature reading -4 degrees. To correct this condition, the vehicle needs to be driven at speeds above 20 mph (32 km/h) for at least 90 seconds. If the concern persists, refer to Workshop Manual Section 413-01 for further diagnostics.

END SSM

Odd, has anyone had this problem? I haven't read about it on here. Really weird issue - sounds like it needs a software fix.

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[benk016]

I wonder what is going on that driving for 20mph for 90 seconds fixes it? Does that do some kind of reset? Seems very odd.

 

[Blanked]

I wonder what is going on that driving for 20mph for 90 seconds fixes it? Does that do some kind of reset? Seems very odd.

maybe it's Similar to the Tire Pressure Sensors and resetting the Dash Alert by driving over 20mph for 90 seconds...

 

[Corsair234]

I haven't had this exact issue, but I'm definitely having problems with the HVAC that seem to be related to the ambient air temperature. At first I thought the AC was broken, but it works when you set it to max. I think it's misreading the ambient air temp (usually it's about 20-30 degrees lower than what Google says on Android Auto) and using what it thinks is cold air from outside to cool the cabin, rather than activating the AC compressor.

 

[benk016]

I haven't had this exact issue, but I'm definitely having problems with the HVAC that seem to be related to the ambient air temperature. At first I thought the AC was broken, but it works when you set it to max. I think it's misreading the ambient air temp (usually it's about 20-30 degrees lower than what Google says on Android Auto) and using what it thinks is cold air from outside to cool the cabin, rather than activating the AC compressor.

I have noticed the car temp and the android auto temp can vary wildly. However, Every time I've realized it, I wasn't home. And android auto was still showing the outside temp at home and not my current location.

 

[breeves002]

I have noticed the car temp and the android auto temp can vary wildly. However, Every time I've realized it, I wasn't home. And android auto was still showing the outside temp at home and not my current location.

I have noticed mine will change 10+ degrees once I start driving after the car has been sitting but I have noticed this in other cars. It is the -4º which confuses me. It really sounds like a software bug that is triggered back into normal operating mode once the temperature changes more than a few degrees or something.

 

[BMT1071]

I wonder what is going on that driving for 20mph for 90 seconds fixes it? Does that do some kind of reset? Seems very odd.

The GM software routine went something like this:

• Save the ambient temp from when you shut the car off.
• Check ambient at next ignition on.
• If new temp is higher, show last temp and wait for ~90 seconds of driving to show new.
• If new temp is lower, show new temp immediately, update as temp increases.

The thinking is that a higher temp may be heat coming off of the radiator. Waiting ~90 seconds allows for airflow across the sensor to balance that out.
It seems the MME wants the drive time regardless of whether the temp is higher or lower. No idea where it would be getting the idea that it's -4 though.
Have you ever noticed what taking your car through a car wash does to the temp display and performance of automatic climate control?

 

[BMT1071]

I have noticed the car temp and the android auto temp can vary wildly. However, Every time I've realized it, I wasn't home. And android auto was still showing the outside temp at home and not my current location.

Glad to know I'm not the only one seeing that with AA. Really freaks me out for a minute when I'm seeing Phoenix temps when I'm in the PNW. ?

 

[AFVolt]

I was just going to post something about this today. Not the -4 part, but the rest applies.

A couple times leaving work in the afternoon I’ve seen it display the ambient temp when I turned the car off in the morning , and it takes awhile for it to update. I watch it quickly climb to the correct ambient temperature during the drive home.

It’s very irksome as it’s cool in the morning and hot later in the day. With the A/C set to automatic it won’t ramp up until it “thinks” it’s hot out.

90+ degree ambient temps are not fun in Florida with the A/C not kicking on because it was 65 in the morning.

 

[Cnote]

I haven't had this exact issue, but I'm definitely having problems with the HVAC that seem to be related to the ambient air temperature. At first I thought the AC was broken, but it works when you set it to max. I think it's misreading the ambient air temp (usually it's about 20-30 degrees lower than what Google says on Android Auto) and using what it thinks is cold air from outside to cool the cabin, rather than activating the AC compressor.

I had a similar issue when I first test drove my car back in mid-March. I was about to turn right back around to the dealership because it was warm in the car. It wasn't until I went in the settings and turned on max ac that things started working correctly. No issues since.

 

[Carsinmyblood]

It's understandable if you think about cars being parked in garages in the winter or blazing heat of summer. Neither represents the weather outside. Same goes for parking garages at malls, airports, etc.

We have the ability to start the car and warm or cool before getting in and driving.

Perhaps the delay allows time to get the car into an actual driving environment before doing anything with the HVAC.....?

 

[sockmeister]

Driving at speeds above 20 mph for at least 90 seconds probably forces/triggers a temperature reading update. They probably do this to avoid skewed temperatures when the car sits in a hot area, for instance.
The -4 degrees thing probably is a default temperature or "missing value" which is definitely a bug, but which will update when the car is driven.

Like others, I have noticed the temperature updating only once I drive the car for a bit.

 

[Luke]

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