Cold weather cruise control and unexpected engine ON

EXECUTIVE SUMMARY

In specific conditions, cruise control can enable the engine to come on and cycle while showing "EV Mode":

	CC-Set	CC-On @35 mph	CC-On @45 mph
1	CC-Set @35 mph	engine stays off	engine stays off
2	CC-Set @45 mph	engine stays off	engine comes ON​

Example:

Use "," and "." to space through the video one frame at a time.

Testing with my 2017 Prius Prime Plus shows it requires cold-soaking the car at or below 48F (8C) with battery SOC 96-100%. The heater was off and the engine cycling did not change it. In contrast, "Front Defrost" turns on the engine and heater controls. Temperatures under 32F (0C) may inhibit the effect. We know the engine comes on at 14F (-10C).

METHODOLGY

The best approach uses two parts: (1) conduct a test and then; (2) reach ~45 mph and cycle the cruise control to verify the engine comes ON. This two part scenario ensures nothing else inhibited the symptom.

We don't know all of the limits:

• lowest temperature - @john1701a and @Lee Jay testing suggest there is a lower limit
• SOC limits - the tested range <80% and >=96% suggests the limit is within 81-95%.
• lowest speed limit - lies somewhere between 35 and 45 mph
• how to stop engine - power cycling the car may stop the cycle and leave the engine off

Use a cell phone, dash cam or video recorder to monitor the test to avoid distracting the driver. Testing after sun set or before sun rise works best because the instruments can be easily read as well as the front view. Video recording can be done during the day with careful setup but test the video setup before testing the car.

SUMMARY

Once started, the engine cycle burns gas and reduces MPG. However, it can easily be defeated by turning cruise control ON when the car is first started.

Thanks to @priuscatprimeguy and the thread he started, ICE comes on anyway | PriusChat who first identified the bug. There were some early driving notes but I can find no effect for stops, speeds, or maximum accelerations.

Bob Wilson

 

because my car didn't charge last night. It was at 52% when I left for work and I typically use 55% getting to work.

The battery ran out on that 6% uphill grade at 55mph just before I got to work. I was on cruise the entire time. ICE didn't kick in until 0.0 miles remaining. The car was in a 53°F garage all night, and the temperature outside on my way to work was 33°F.​

The engine ON we're tracking requires SOC greater than 80% and cold-soak temperature under 48F. What you've described is the normal engine ON when SOC is exhausted.

Bob Wilson

 

I'm not sure I understand:

Perhaps you might use Google Earth and share a graph of the hill and/or route?

Bob Wilson

 

I went back and reviewed YouTube cold morning commute to work (see after signature.) It looks like after the right-turn at the first stop sign, you can reach 44 mph with 98% SOC. Could you wait until reaching 44 mph before turning your cruise control ON and SET?

That would match the protocol that leads to turning the engine ON.

A minor technical point, it would help if the instrument display could include a couple of inches to the right that includes the cruise control icons. I notice the edge of some icons at seconds 0:06. I would not want to lose what you have already on the left, just I'd like to see the cruise control icons too ... if possible. It may be impossible to get the camera back far enough to see the full instrument display.

I ran into a similar problem so this is how I mount my dash cam to get both the windshield and at night, the instruments. Daylight wipes it out.


It appears to be a time-lapse video. It would help if we could get some time stamps and/or give an idea of the frame sampling rate. Know the true times makes it easier to see if there might be a time component.

Thanks,
Bob Wilson

ps.

 

Let me suggest following the protocol in the first post so you can experience the symptom. Once you understand what happens, we can use experiments to measure the limits and add details.

We've not really dug into OBD data and if you'd like to start, go for it. The key is to find any OBD metrics associated with the symptom.

Bob Wilson

 

I replicated the symptom at 42 mph earlier today. This is a critical threshold speed in the earlier Prius between hybrid-mode with engine OFF and engine must run.

Bob Wilson

 

So today I tried:

• Cruise control ON while stopped, right after READY
• Cruise control SET at 44 mph -> engine came ON!

I was not expecting this.

Next cold soak, I'll try cruise control ON and SET at 35 mph. If the engine remains off, I'll use the stalk to increase the speed to 44 mph to see if the engine comes on.

I really want to find ways to use cruise control in cold weather without risking engine ON.

Bob Wilson

 

I’ll add it to my list.

BTW, testing dynamic cruise control ON and SET at 35 mph did not start the engine. Using the stalk to increase speed to 45 mph did not trigger an engine ON event. Shortly I'll try the 35 mph ON+SET and then accelerate to 45 mph and try SET again.

Bob Wilson

 

I'll try again but ON+SET at 35 mph didn't force engine ON this morning. But I was already using the heater to help defrost the windshield.

Bob Wilson

 

With temperatures in the 28F (-2C) range, the engine ON happened at 33 mph and lasted much longer, 5-6 miles vs 2-3. My past tests were warmer and often intermittent.

• Use "," to backup one frame and "." to go forward.
• "Use on Expressway Only" signals cruise control is ON
• The graphic lane with three bars, car, and speed signals cruise control is SET

The only known workaround is to NOT use dynamic cruise control in cold weather. However, probability goes down as the temperature rises up to 50F (10C). Another factor, it is less likely as the battery SOC decreases from 100% and seen as low as 96%.

Bob Wilson

 

EXECUTIVE SUMMARY (V1.01)

In specific conditions, cruise control can enable the engine to come on and cycle while showing "EV Mode":

	CC-Set	CC-On @33 mph	CC-On @47 mph
1	CC-Set @33 mph	engine ON​	engine stays off
2	CC-Set @47 mph	engine stays off	engine ON​

Examples:

Use "," and "." to space through the video one frame at a time.

With temperatures in the 28F (-2C) range, the engine ON happened at 33 mph and lasted much longer, 5-6 miles vs 2-3. My past tests were warmer and often intermittent.

• Use "," to backup one frame and "." to go forward.
• "Use on Expressway Only" signals cruise control is ON
• The graphic lane with three bars, car, and speed signals cruise control is SET

With temperatures in the 28F (-2C) range, the engine ON happened at 33 mph and lasted much longer, 5-6 miles vs 2-3. My past tests were warmer and often intermittent.

My first video with a GS63H dash cam:

It happens at 1:54 into the video.

Testing with my 2017 Prius Prime Plus shows it requires cold-soaking the car at or below 48F (8C) with battery SOC 96-100%. The heater was off and the engine cycling did not change it. In contrast, "Front Defrost" turns on the engine and heater controls. Temperatures under 32F (0C) may inhibit the effect. We know the engine comes on at 14F (-10C).

METHODOLGY

The best approach uses two parts: (1) conduct a test and then; (2) reach ~45 mph and cycle the cruise control to verify the engine comes ON. This two part scenario ensures nothing else inhibited the symptom.

We don't know all of the limits:

• lowest temperature - @john1701a and @Lee Jay testing suggest there is a lower limit
• SOC limits - the tested range <80% and >=96% suggests the limit is within 81-95%.
• lowest speed limit - lies somewhere between 35 and 45 mph
• how to stop engine - power cycling the car may stop the cycle and leave the engine off

Use a cell phone, dash cam or video recorder to monitor the test to avoid distracting the driver. Testing after sun set or before sun rise works best because the instruments can be easily read as well as the front view. Video recording can be done during the day with careful setup but test the video setup before testing the car.

SUMMARY

Once started, the engine cycle burns gas and reduces MPG. However, it can easily be defeated by turning cruise control ON when the car is first started. The only known workaround is to NOT use dynamic cruise control in cold weather. The probability goes down as the temperature rises up to 50F (10C) when it stops. Another factor, it is less likely as the battery SOC decreases from 100% and seen as low as 96%.

Thanks to @priuscatprimeguy and the thread he started, ICE comes on anyway | PriusChat who first identified the bug. There were some early driving notes but I can find no effect for stops, speeds, or maximum accelerations.

Bob Wilson