Are the TPMS's cloned so the system recognizes the sensors? If they are not, you have to have them reprogrammed every tire swap.

Possibly the others were cloned?

 

The tire pressure sensors are original, on the original wheels, original tires. Tire pressures have been checked, are OK. I do not have tire pressure sensors in the snow tire wheels. Again, I have never had this problem before last year with this Forester.

 

I have a 2018 Forester Limited edition. I have dedicated snow tires on wheels, and have had dedicated snows on wheels since I bought my first Forester in 2013. For the first two years the low tire pressure warning light went out when I changed over. Last year, the damn light stayed on, so I had the dealership fix it when I went in for service.

Today I swapped over to summer tires, and the same thing happened. I drove about three miles and the light is still on. I'm wondering if I could fix it using a car fault reader. Clear the fault, and when the computer comes back online it doesn't see the fault. I asked the service advisor what the problem was and he didn't know.

Anyone have a clue?

My household has three cars, all with dedicated snow tires on wheels. This 2018 Forester is the only car that has ever had this problem.

Ya I believe you need to drive more than 3 miles like the other post said. I think you also have to go above a certain speed too, probably above 25 mph. If sensors are still good, the light should go off automatically.

 

Ok, that clears it up. You need to drive about 10 miles to get the light to clear assuming the sensors are still good and the pressure is correct.

I did the same with my 2010 Impreza. Had the light during the summer, and no light in the winter. I had sensors in the winter tires programmed to the car, since it was more of a winter use than summer.

 

Mine have always gone off pretty quick after the changeover.

When DOT did the TPMS rulemaking, the cost/benefit analysis did not include the winter tire situation and it lowballed the other costs such as sensor replacement when batteries expire.

 

Forgot to mention, when I had problems with needed a couple P:SI extra pressure to keep the light off, dealer response (under warranty) was that they are all that way.

 

It's also possible a sensor went bad.
If the problem doesn't go away on its own, have a tire store check that the sensors are transmitting..
Some of the better shops will do that for free.

 

Your original post wasn't all that clear. You lived with the light on all winter while driving with the winter tire package that did NOT have sensors. In the Spring when you put the OE set back on, the system sync'd back up and the light went out.

Last year it didn't work, and it took dealer intervention to get it working. Same is happening this year.

One of several reasons:

1) As was said, you might not have run the OE set long enough yet. It shouldn't take more than a few miles, but sometimes a sensor is slow to wake up.

2) Have you checked tire pressure on the summer set? Solidly in the safe range?

3) You could have a marginal sensor.

4) The RKE/BIU that receives/processes the TPMS sensor data could have an issue and might be dropping hex ID data or the fault code from the winter is not being deleted allowing the system to process correctly. Cxxxx codes can be difficult to clear without a scan tool with the right access to proprietary systems. Try a tire store. They will usually make an attempt at a nominal cost. Well less then the dealer. They can probably tell you if the sensors have a battery issue or are slow to wake up, or if it is a DTC stored that needs to be cleared.

 

Update: My tires were all up to the correct pressures and I drove far enough for the sensors to connect up with the computer. So, I called the service advisor I deal with at Subaru and asked him what they did last year to get the light to go off. He said they had to reprogram the sensors into the computer, and that's what needs to be done again now. He told me they would do it for free as I bought the car from them and have it serviced regularly with them. The question is why would the data drop out of the computer when it didn't before last year?

 

Driving without a TPMS sender will set an error code in the ECM and that needs to be cleared when you change back to your other tires.

 

That was my guess, but that's now what he said. Question: Will removing the battery connection and then replacing it clear the code? I don't have a code reader.

 

I don't know. I have always cleared mine with a TPMS scanner.

 

Interesting, I never had any issues with my 2010.

Edit: But then I had sensors in the summer tires, just not programmed to the car.

Maybe that's the difference.

 

Normally, running a set of tires for a few months without TPMS sensors just sets a simple code like C2121, indicating that it isn't getting a signal from a sensor. As soon as you put the tires with sensors back on the car that are transmitting, that code erases itself. And as @MJK914 said, that's how it worked for the first few years. Restore the tires with sensors, and the system sync's right back up.

Sometimes a more serious communications error code can be set that will not auto-delete. Rare, but it can happen. It is more likely to occur on a 2019+ system with the full dash display (more complex sensing), but can occur on older models with just the dash light.

System level electrical interference can also increase the likelihood of a 'stuck at fault error' that needs to be cleared before it will resolve. Crappy cheap cigarette lighter USB +5V supply plugs can induce this.

 

Thanks for the info. I sometimes use a GPS which plugs into the cigarette lighter for power. That could provide the system level electrical interference you mention. I drove my wife's 2017 Camry yesterday after switching her tires back to summer tires with sensors, and the tire pressure levels came back on line. However, she never uses the GPS unit in her car. My daughter will be up to visit with her 2018 Legacy 3.6 Limited. She also has dedicated snows on wheels. We shall see if she gets the same problem I have.

 

The older pre 2019 TPMS does have individual pressure readings, it's just that Subaru elected not to display them.

With a decent aftermarket HU, and an OBD connection/adapter, you can get the individual pressures on your HU. At least I could on my 2010 Impreza.

So it isn't as basic as Subaru made the display.

 

The older pre 2019 TPMS does have individual pressure readings, it's just that Subaru elected not to display them.

In reality, every single vehicle made with TPMS that has DTC logging capability has this. 2007 +/- to present. In order for the canbus system to operate and monitor operation, the system has to capture the digital output of the 4 sensors and compare the values to the set threshold. So all the data is there.

I used Techstream (like Subaru Select Monitor) on my 2008 and 2015 Toyota Sienna to do live monitoring, even though the Sienna did not get a digital dash display until the 2021 model year.

What was missing, and why many manufactures were hesitant to include a dash display, was which tire was which. Techstream or any OBD port system will typically just say Tire 1 / Tire 2 / Tire 3 / Tire 4. Without PAL to a single antenna or a set of 4 distributed antennas, there is no good way to track where the transmission is coming from.

 

There are a lot of customizable features listed in the chipset designer kits for the car manufactures to select from. Few are chosen. I just can't see too many vehicle owners sitting at an air pump and feeding in quarters for 2 minutes of air while bleeding out, fiddling with a dash menu, and then refilling tire after tire.

The Japanese marks tend to vote as a block. For years, most models came to the USA with just an amber light. Given what you described, I can see why....

 

I have a very nice portable 12 volt compressor I made from an air ride suspension pump.

The ability to see individual tire pressure was just a side benefit to upgrading the audio system.
I wasn't even aware it could do that until I played around with the features.

So depending on circumstance, it can either be not worth the expense, or just making use of what Easter eggs you have lying around.

But I agree most people aren't going to go to the trouble. Or the expense just to see tire pressure.

But my point was the early system was not a simple design. Just the warning method was.

I was surprised GM bothered on a bottom level van.

It was also a matter of toggling through screens to find it. Not too different than what the SK display is now. Maybe just a little more difficult.

 

We get spoiled, don't we? I have a vertical tank compressor with a hose up to a garage ceiling mounted 50 ft retractor reel air hose to support my pneumatic impact tools and tire filling. Of course, 20+ years later most work I do is with a battery impact driver and not by air.....

And because I was just too lazy to run a hard copper line from the garage down to the basement to support my bicycle repair activity, I ended up buying a little pancake compressor to sit next to my repair stand.

As I've said before, TPMS systems are complex and the implementation often leaves a lot to be desired.

 

@MJK914 if there is a store location near you, give them a visit. They will verify sensors are working and can reprogram if necessary at no cost to you.

 

Thanks for the tip on Discount Tire. It's hard to believe anyone would do something for free. I just checked onlline and there are no Discount Tire stores anywhere near me. Oh well.

 

I've never dealt with Discount Tire, but they do seem like standup citizens. Companies do things like this to win you over as future customers. It's a good business practice. Tire Rack (now a Discount Tire subsidiary) and Mavis Tire won me over years ago by offering something for low cost or free when I needed it, and that's where I tend to return to for the next purchase.

That said, many small businesses will do a quick check for you in hopes of future loyalty. Car parts stores lend tools and often will read out a DTC code. They assist you, and you buy the repair parts from them. See if a local tire shop will help you. Many will do a quick TPMS check for free. Remember to give the kid who helps you a generous tip for his time and effort.

 

My local Subaru dealership programmed my winter wheel sensors for a $30 charge, but no promises they would work.

They worked fine though...

 

@Fibber2 thank you for your kind words. Discount Tire has always done R.M.A. approved flat repairs at absolutely no charge for our customers. You might expect to pay more for such conveniences, but with our Low Price Promise, you never would. We appreciate your consideration and look forward to serving you in the future.