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Yaris - Fluctuating Alternator Output


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I have a very strange problem with my 2009 Yaris T2 1.0 (without aircon). After driving for 5 - 10 minutes, the heater blower will suddenly slow down on it's own, thereafter if I lift my foot off the accelerator, after a 1-2 seconds delay, the fan will return to it's normal speed. If I press my foot on the accelerator the fan speed will slow down again. It does it on all fan speeds but is most noticeable on number '4'

If I have the lights turned on the fan stays at a constant speed and the problem does not occur.

The dealer has replaced the blower motor and rheostat, but it has not cured it. Iam currently waiting for a Toyota field engineer to look at it.

Dealer has had the car for 6 days and still can't fix it. Has anyone else had this problem? If so what was the cause?

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You noticed any other faults on your car? If you put the interior light on and try it do you notice if the light dims in sync with the blower motor speed?

No if I put the interior light on it does not dim in sync with the heater blower speed. However, when the blower slows down and I then turn the sidelights or headlights on the blower speeds up to it's correct speed. If I turn the lights off it slows down again!

With the lights turned on the blower stays constantly at it's correct speed.

The fluctuating blower speed only occurs when the lights are turned off, this is when the blower speed increases if foot is taken off the accelerator and slows if I press the accelerator.

None of the dashboard lights dim in sync with the fluctuating blower speed either.

There are no other faults with the car.

The dealer has changed the blower motor & rheostat, so really all that is left as suspect is the relay, alternator voltage regulator or a wiring harness fault.

The field engineer from Toyota G.B. is going to look at the car next Tuesday and run some tests on the electrical system.

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  • 2 weeks later...

Will be interested to see the outcome of this.

The Toyota field tech narrowed it down to the alternator..also the interior light does dim in sync with the blower speed - I couldn't see it doing it but apparently it did - new alternator fitted today and the dealer has just phoned me to tell me it has NOT cured the problem! :angry:

Will update as soon as I hear from them.

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Had a phone call from Toyota dealer today. Apparently they have found a bad earth.

They have today fitted an auxillary earth strap from the blower motor to the car.

The reason being that they now think there is a fault with the earth wire in the car's multiplex wiring harness and by doing this is it will prove whether this is the case.

(They have changed every other component in the system)

I have to run the car for a few weeks and see if this has cured the problem.

Everything is checking out o.k. now with the voltage.

If this turns out to be the problem they are going to fit a complete new wiring harness.

The temporary earth strap has not cured the fault. It is doing it as bad as ever - on top of this I noticed a kind of 'plasticy' burning smell when I first started the car this morning.

The fluctuating heater blower speed is a symptom of a seemingly untraceable fault with the car's electrical system.

Iam a very unhappy Toyota customer.

Back to the dealer on Monday - They have had my car on 4 occasions for a total of 10 days and made 5 attempts to repair it - my patience has just run out!

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Car is back in to Toyota for the 5th time in 5 weeks! They have assured me it will definitely be solved this time and I will not get the car back until it is.

The tech that has been assigned to deal with it suspects the car's ECU is faulty.

Hopefully my next post about this will be the final one.

UPDATE: 8-10-10 They have had the car all week and phoned me tonight to say they have still not been able to fix it they need to speak with Toyota G.B. on Monday :ffs:

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Having a problem with my 09 Yaris (at least the Toyota dealer is)

I first noticed my heater blower speed slowing down & speeding up on it's own- the interior light also dims in sync.

None of the above happens when I have the exterior lights turned on though.

Took it in to Toyota and to cut a long story short the problem is not with the blower, but with the car's electrical system. A Toyota field tech diagnosed the alternator, as it was fluctuating output in sync with the blower fan speed slowing/speeding up.

They fitted a new alternator & it did not cure it.

Needless to say the car is now back with them.

Has anyone else had this problem and if so what did it turn out to be?

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Car is back in to Toyota for the 5th time in 5 weeks! They have assured me it will definitely be solved this time and I will not get the car back until it is.

The tech that has been assigned to deal with it suspects the car's ECU is faulty.

Hopefully my next post about this will be the final one.

UPDATE: 8-10-10 They have had the car all week and phoned me tonight to say they have still not been able to fix it they need to speak with Toyota G.B. on Monday :ffs:

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I hope you get it fixed soon as I can imagine it must be driving you mad.

I had a problem with a Toyota some years ago that was only fixed by trading in for something else ...and it wasn't Toyota. I had no faith in the Toyota field tech who didn't want to fix the problem.

Sounds like yours might take a while to sort, replacing the wiring loom sounds extreme but might be the only answer.

Best of luck

Peter

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I would assume that the dealer had checked for tightness of the battery terminals and other earth points :eek:

Maybe you should ask them!

Hi - Yes they have checked the Battery terminals and all the other leads, wires etc, they have tried new Battery, Alternator, they have had the car for 14 days in total. The service manager suspects there is a fault within the wiring loom and the tech suspects a fault with the ECU. Whichever it is, it will mean it has to be replaced.

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  • 3 years later...
  • 4 weeks later...

Just reading this thread.

A few months ago I had a volt meter plugged into the cigarette socket and monitor the charge voltage. Strangely I noted the voltage could be anywhere between 12.6 to 14.5v. Seems odd.

I later checked the Yaris electrical manual and confirmed that the behaviour is because the alternator only provide an output when the ecu demands it. So Toyota has started to use the Smart alternator.

In my case there was no fault it is normal behaviour.

In your case the fault is likely to be the alternator or the ECU.

The ECU controls the demand of the alternator how much output to the Battery and load.

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I have been checking my fluctuations and only seems to happen when the heater blower is set on the second to last setting, but not on full setting. I can only assume therefore it must be an hr connection for that setting, wear and tear I assume as this was probably the preferred setting for previous owners.

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I just read the entire thread. The guy said he smell some plastic burning when he started the car in the morning. I think this is the clue. It's more likely it's the wiring loom have a fault.

If the problem doesn't bother you too much leave it alone, as it will be very expensive job to fix.

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