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Vampire TPMS light on at night


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Hi guys, hope someone here can provide some insight.

 

About a month ago, my 2013 Subaru Legacy 3.6R Limited TPMS light start to comes on at night (after sundown). TPMS light comes on at around 8-10 minutes mark.

In the morning, the light will stay lit for about 3-5 minutes and TPMS light will go off.

 

Action taken:

OBD scan shows no code. I scanned it when the light is on at night , and scanned it again when it's off.

 

Took it to dealer on 10/18/16, show them the video of the issue. They did a diagnostic but return no codes. They reprogrammed the sensors and told to come back when the light comes on. On 10/18, light comes on at night. Took a video of it and back to the dealer.

 

On 10/20, dealer said, they can't do anything because there is no codes. They told me to call Subaru of America and open a case. That's what I just did. Hope for the best.

 

Have anyone encountered this before?

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What are your tire pressures?

 

So you're saying that when the car is off, the light comes on?

 

Also, moved this to the 5th Gen section.

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My guess is the tire pressure (in at least one of the tires) being right on the edge of triggering the sensor. As it cools down at night, the pressure drops, and the sensor is triggered.

 

Every 10F = 1 psi

 

Just to rule that out, go drive the car on the highway a bit, then check your tire pressures. They should all be about 4 psi higher than the number on the door sill when "hot". In other words, when the tire is "hot", the pressures should be about 37-38 in the front and 36 in the rear. Since some [better] tires dissipate heat better than the OEM tires, they tend to stay cooler resulting in less dynamic pressure increase, resulting in chronic underinflation.

 

If you still have issues then maybe you just have 1 or more bad TPMS sensors. I doubt that would throw a code.

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I have a bad tpms sensor, or dying battery in one. Usually it stays off until I drive a long distance 25 min or so then it comes on, sometimes it will come on and flash slowly for a while and then stay on. Sometimes it goes back off after a little while. My tires are all inflated well above the limit to turn the warning light on. One day I will replace them all.
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What are your tire pressures?

 

So you're saying that when the car is off, the light comes on?

 

Also, moved this to the 5th Gen section.

 

 

Tire pressures are 33 and 34psi.

 

This happens when I am driving. When the lights come on, I pulled over and took the pressure ~ 36 psi.

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My guess is the tire pressure (in at least one of the tires) being right on the edge of triggering the sensor. As it cools down at night, the pressure drops, and the sensor is triggered.

 

Every 10F = 1 psi

 

Just to rule that out, go drive the car on the highway a bit, then check your tire pressures. They should all be about 4 psi higher than the number on the door sill when "hot". In other words, when the tire is "hot", the pressures should be about 37-38 in the front and 36 in the rear. Since some [better] tires dissipate heat better than the OEM tires, they tend to stay cooler resulting in less dynamic pressure increase, resulting in chronic underinflation.

 

If you still have issues then maybe you just have 1 or more bad TPMS sensors. I doubt that would throw a code.

 

I check the tire pressure when cold = 33 psi and 34 psi. My commute is 40 miles each way, so when I get home, check again ~36 psi.

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I have a bad tpms sensor, or dying battery in one. Usually it stays off until I drive a long distance 25 min or so then it comes on, sometimes it will come on and flash slowly for a while and then stay on. Sometimes it goes back off after a little while. My tires are all inflated well above the limit to turn the warning light on. One day I will replace them all.

 

If sensor battery is the issue, then how come it does not happen during day time.

 

TPMS sensor only come on at night. :spin::confused::confused:

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They only come on when driving, and its not instant that the ecu will light up the warning all the time. It may just be a coincidence it is coming on at night, or maybe something to do with the ambient temp affecting a connection on the circuit board of the sensor.
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They only come on when driving, and its not instant that the ecu will light up the warning all the time. It may just be a coincidence it is coming on at night, or maybe something to do with the ambient temp affecting a connection on the circuit board of the sensor.

 

It comes on at night no matter what the temperature is? I was in Brentwood temp in 80's, or Pacifica 40's.

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Sounds like an electrical issue. When you say at night, I think of headlights and cluster. The circuit board in the cluster could be faulty. If it does not come on during the day, turn on your headlights and see if the light comes on. That would be a really quick way of isolating the problem.
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Sounds like an electrical issue. When you say at night, I think of headlights and cluster. The circuit board in the cluster could be faulty. If it does not come on during the day, turn on your headlights and see if the light comes on. That would be a really quick way of isolating the problem.

 

I tried that earlier in the day..driving with my headlight, foglight on..NO TPMS light

 

I also did the opposite, driving at night with no light on in the parking lot...TPMS light comes on around 9 minutes. :spin::spin::spin::spin:

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If sensor battery is the issue, then how come it does not happen during day time.

 

TPMS sensor only come on at night. :spin::confused::confused:

 

The TPMS sensors are using radio so if you have something that goes on causing RFI (Radio Frequency Interference) under some conditions then that may cause it. Any strong radio station in the neighborhood - or ham radio operator that is active during the nights? TPMS sensors come in two frequencies: 315MHz and 433MHz - and 433MHz is in the UHF ham band.

 

And if you have a spare with a TPMS sensor that may be the culprit.

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The TPMS sensors are using radio so if you have something that goes on causing RFI (Radio Frequency Interference) under some conditions then that may cause it. Any strong radio station in the neighborhood - or ham radio operator that is active during the nights? TPMS sensors come in two frequencies: 315MHz and 433MHz - and 433MHz is in the UHF ham band.

 

And if you have a spare with a TPMS sensor that may be the culprit.

 

It happens everywhere. Tahoe, Sacremento, San, Jose, Disneyland. Always no issue on day time. Always issue at night. It's been going on since 9/15/2016.

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Ok.. so the question is... Is there a relationship between time of day and the behavior, or light conditions.

 

Try taking the car some place dark in the middle of the day. Do you have a dark garage?

 

I can cover up the garage, but CO2 is another problem.

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In that case I'd start to suspect that you have a bad TPMS sensor that is temperature sensitive - or that the receiver is temperature sensitive since it's usually colder at night.

 

It can actually be that it's the ventilation system that heats the receiver when it's starting to turn on heat because it's cold outside - so try to run full heat during day and see what happens. Try different fan settings too.

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The receiver is on the rear deck, no?

 

Regarding the comment about CO2. I assume you actually meant carbon MONoxide. Does the car have to be running to experience this? Just key on no?

 

Try this: During the day, put black electrical tape over the sun-load/auto-headlight sensor. Confirm its reading darkness by putting your headlights to auto, then turn them off.

 

If this triggers the problem, then either someone crossed some wires while fixing something electrical (sun-load sensor "fixed" recently?) or... There is logic in the BIU to check and report on bad TPMS sensors only when it gets dark, or your BIU is going nuts.

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