The Cruise Control Seems to Have Problem!?

[cow]

Hi,

We've brought a 2009 Tarago. My wife just told me that the cruise control seems to have problem.

For example, when she turned on the cruise control and set the speed at 80km/hr. It worked fine until the car went down a slope in Melbourne East Link Tunnel (which is just a small slope). The car kept accelerating and when she noted that, the car was driving at 100km/hr inside a 80km/hr limit tunnel. She was scared. Similar issues have happened several times in different places.

We have been driving Toyota for more than 10 years and this is my third Toyota car. This problem didn't happen in my previous Carmy Sportivo. I am not sure if this is normal or not, but I do think it's very dangerous. Because of this, she need to keep her eye on the speedometer when using the cruise control, which is quite disappointed.

Besides, the speedometer doesn't display speed correctly. For example, it displays 100km/hr, but my actual speed is about 90km/hr. I told the dealer when I had my first service. They said it was normal and they wouldn't fix it because the different was less than 10%.

There are two problem seems to cause safety issue:

1) The speedometer is not accurate.

2) The cruise control fails to control car speed.

Do you have similar issues?

Thanks.

[Blind Kid Seeks]

what was Toyota's response to your concerns?

[Ascendant Rice]

speedos are never 100% accurate.

cruise control doesnt brake for you.

[DJKOR]

speedos are never 100% accurate.

cruise control doesnt brake for you.

Pretty much what I was going to say. With the speedo, it's common for manufacturers to have speedos that read higher than your actual speed. As there is always going to be some error when it comes to speedos, it is better to be biased towards the safer side just in case. It also helps them in away because they then can't really get any blame for any speeding tickets due to a inaccurate speedo.

As for the cruise control, without driving the slope myself, I can't make a comment but going down a slope and the vehicle gaining speed isn't anything out of the ordinary. Especially when you are talking about a larger vehicle like the Tarago. Due to the systems involved, cruise control only takes care of the throttle and has nothing to do with the brakes.

[Silver-Aurion]

We used to have an old holden station wagon that was fitted with an aftermarket CC. When the car was set at a speed and we started to go downhill and the speedo was going higher, the car's engine would be used to slow down the car to reduce speed. Like engine breaking.

You never needed to look at your speedo because downhill or uphill the car would slow down and speed up again.

But now with new cars, cruise control seems to do jack **** other then keep a constant speed, and the tiniest slope on the road the speedo starts shooting up.

To the OP, the dealer can't do anything, because thats actually normal operation of the vehicle, if it did anything else besides what you mentioned something would be odd.

[Milgram]

You are unlikely to get much support from Toyota because your Tarago is functioning as designed.

I am familiar with the Eastlink tunnels and have driven both new and old vehicles fitted with cruise control through them. As others have stated, OEM cruise control systems will not brake for you, they will just cut the throttle on downhill sections because they sense the speed rising. Those tunnels do have a steep descent and I find it is better to control the speed myself (i.e. not use cruise control) given there are speed cameras as you reach the bottom.

I have spoken to Engineers in the past about cruise control and many recommend using it on flat sections of road only. The reasoning behind this is on uphill sections, the cruise control can make the engine work harder than necessary to keep it at the set speed (and subsequently use more fuel) and on downhill sections, it is better to control speed yourself incase the cruise becomes stuck on.

Edited February 11, 2010 by JMacca53

[peregrine]

We've brought a 2009 Tarago. My wife just told me that the cruise control seems to have problem.

1) The speedometer is not accurate.

Do you have similar issues?

The difference to speed you quoted ie doing 90KPH and reading 100KPH shows an error of over ten percent so if 10 percent is the criteria then it should be fixed. However, are the tyres and wheels, as supplied by the maker? You could overcome the speedo error to some degree by fitting slightly larger wheels or Tyres or higher profile tyres. Tyre shops should be able to calculate a right mix. Be careful not to exceed regulations. As has been well covered here cruise controls don't supply stopping power but I believe there is the possibility of gaining some engine retardation if taken out of overdrive. not sure if this works with cruise control on though.

[cow]

Thank you for all your reply.

I have already sent email to Toyota but haven't heard from them so far.

I tried to hear advices from different sources so that I could have a better understanding of it.

hmmm, it looks like the cruise control doesn't like uphill and downhill. They should have a warning message somewhere on their website or user manual.

This is a new car without any external modification. I drove on freeway at 100km/hr (according to the speedo), the other cars kept overtaking me. I checked my GPS speed, it show about ~90km/hr. I needed to drive to 110km/hr (the GPS show ~100km/hr) before I can keep up with all the cars. The situation also happens when I drive in city at 60km/hr. I need to drive above 60km/hr (~65km/hr according to the speedo). I think you know what will happen if you drive too slow in the city road. I think it's biased towards the safer side too much.

I will let you know once I got any feedback from Toyota.

Thank you

[danja]

Some luxury vehicles (eg Lexus) have braking incorporated into their cruise control, but generally speaking it's true that most CC systems simply control the throttle to keep the car at the minimum set speed.

The logic is very simple:

- if actual speed < desired speed, open throttle and speed up;

- if actual speed > desired speed, close throttle (which might cause you to slow down depending on what gear you're in, current speed, and the gradient of the road);

- if actual speed = desired speed, maintain slight throttle opening to keep constant speed.

Think about it this way, if you were just driving along without CC enabled, and came to a downward slope - if you took your foot off the accelerator, would the car speed up or slow down? You'll experience the same thing with CC.

Regarding your speedo - how are you establishing that 100 indicated km/h = 90 actual km/h? Factory speedos always understate slightly, 10km/h is extreme, but 2-3 km/h is common. Tyre wear will affect this slightly too, to the tune of 1-2% - and if you've fitted aftermarket wheels, it could be much more.

[cow]

After reading all your comments, I think i know what's happening of the cruise control.

It looks like this is normal. The car is new (new car runs smooth) and much bigger when comparing with my old Carmy Sportivo, which make the accelerating effect more noticeable.

For the speedo issue, I use my TomTom and Nokia 6110 to check the speed. I also compare my speed with the other cars on the road. This is what I can do. I know it's not accurate, but it's consistent.

Thanks.

[httttt]

I don't want to repeat what everyone else has already said but you still have to look at the speedo when using cruise control and failing to do so on the basis that that the car should "know better" is silly.

I have noticed in my Aurion that going down hill I will often need to use the break to regular speeds where the speedo switches its self off, by the time the CC needs down gear to slow the car it is already going much too fast. They have a thresh hold of around 5kmph, if the car goes above or below that thresh hold the CC will switch off.

Gearing down to slow the car down at speeds of over 100kmph will usually result in slowing the car down too much. It is very rare that my Aurion gears down.

[danja]

For the speedo issue, I use my TomTom and Nokia 6110 to check the speed. I also compare my speed with the other cars on the road. This is what I can do. I know it's not accurate, but it's consistent.

I'm inclined to think your speedo is probably working fine. GPS units are not 100% accurate as some people think, the system is in fact designed with a margin of deliberate error. They are "close enough", but don't take them as gospel. Again, judging by other traffic is no exact science either, as most cars will be going a little over or a little under the limit.

If you think it's really serious, and bothers you that much, see if you local traffic authority or mechanic can recommend a mob who do speedo calibrations.

[DJKOR]

Also, I wouldn't be comparing your speed with others on the road. I've done a fair bit of driving and have realised that speeding is so much more common than you think. There are so many drivers out there that exceed the speed limit by 1-10km/h because everyone these days is always in a hurry.

[cow]

Just got the reply from Toyota:

==========================================

"The speedometer in your vehicle is produced and calibrated according to Australian Design Rule (ADR) 18/03, which states:

- Vehicle speedometers to indicate a speed equal to or higher than actual vehicle speed and no more than 10% + 6 km/h higher than actual speed.

For example: If the actual vehicle speed was 100km/h, the vehicle speedometer must indicate no less than 100km/h and no greater than 116km/h.

==========================================

So, my speedo is normal and still within the limit.

Not very happy with their Answer, but not much I can do.