Disconnecting battery deleted custom TPMS setting?

[Jebb]

I purchased my truck with dealer-installed "oversize" 35x12 tires. The dealer re-programmed the TPMS setting to 35 psi. I ALWAYS kept these tires at 35 psi and never had any trouble or warning until they went below 32 or so on cold days. I never even knew the door sticker says 39 because I always THOUGHT it was supposed to be 35!

Recently I disconnected the battery to do some work and now the TPMS warning comes on every time I start my truck saying "inflate tires to 39 psi". It seems that somehow disconnecting the battery reset the TPMS settings back to stock.

How did that happen? I thought ECU programming was "non-volatile"?

 

[04fxdwgi]

That programming isn't in the ECM, it's in the BCM and yes, it "normally" is non-volatile. It can be changed with AlfaOBD.

Have no idea why it would mysteriously change by itself.
Mine is set at 39,39,0,0 from the factory

 

[Jebb]

That programming isn't in the ECM, it's in the BCM and yes, it "normally" is non-volatile. It can be changed with AlfaOBD.

Have no idea why it would mysteriously change by itself.
Mine is set at 39,39,0,0 from the factory

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Been looking into AlphaOBD. In your screenshots here what is the "Light load inflation pressure" and why is it set to zero?

 

[RamDiver]

Been looking into AlphaOBD. In your screenshots here what is the "Light load inflation pressure" and why is it set to zero?

I checked my System ID files and found mine to be set the same.
I haven't tweaked those settings, so they must be the OE default config.

Max Load Inflation Pressure Rear Tire (0-126PSI): 39.000 PSI
Max Load Inflation Pressure Front Tire (0-126PSI): 39.000 PSI
Light Load Inflation Pressure Rear Tire (0-126PSI): 0.000 PSI
Light Load Inflation Pressure Front Tire (0-126PSI): 0.000 PSI

.

 

[Dean2]

You did not have custom settings that reset. At 39 pounds programed in, they alert at 20% pressure loss, so 7.8 lbs. Alerts at 31-32. Once it alerts, you have to pump it back to 39 drive or wait with key on. Once the light goes out, you can reduce to 35 and it will be fine as long as cold doesn't drop the tire to 31-32.

 

[Jebb]

You did not have custom settings that reset. At 39 pounds programed in, they alert at 20% pressure loss, so 7.8 lbs. Alerts at 31-32. Once it alerts, you have to pump it back to 39 drive or wait with key on. Once the light goes out, you can reduce to 35 and it will be fine as long as cold doesn't drop the tire to 31-32.

I raised all 4 tires to 39 PSI yesterday morning and drove on them for about 10 miles. This morning I got the TPMS chime again saying low tire. Showed 2 tires at 37 and the other two at 39. So 37 is still not enough? It's weird that this chime doesn't clear automatically once you get back above that 20% lower limit (31-32). I don't understand the rationale for that but...

OK. Will try raising all to ~40 - see if it clears - then lower back to 35. Thank you for the info.

 

[04fxdwgi]

I did the 40-41 and the *&&^% light is still on. Have no idea why.

 

[Dean2]

If you have a sensor going bad that will set the light too. If you vehicle is 5 or more years old that is very possible.

 

[04fxdwgi]

Sensors test good (bought a tester) and display shows correct pressures.

 

[62Blazer]

You did not have custom settings that reset. At 39 pounds programed in, they alert at 20% pressure loss, so 7.8 lbs. Alerts at 31-32. Once it alerts, you have to pump it back to 39 drive or wait with key on. Once the light goes out, you can reduce to 35 and it will be fine as long as cold doesn't drop the tire to 31-32.

I was going to say the same thing. If you have always got the alert at around 32 psi the target pressure was probably still 39 psi.
To the OP, after you pumped up the tires and drove 10 miles did the alert turn off and then only reset the next day? Or did the alert never turn off? One thing I have found is that the vehicle display rounds everything up. Meaning if you only put 38.5 PSI in the tires the screen rounds up to 39 PSI, but the BCM (computer) is only reading 38.5 and not the full 39 that is required......at least I believe that has happened to me a few times in the past. I've gone back and put just a little bit more air in the tires and they reset.
As another post stated, if the target pressure is 39 psi and the alert doesn't trigger to 32 psi.......once that alert is set you have to pump the tires all the way up to the target pressure to reset the light. Just going back up above the low limit, like 33 psi, does not reset the light. This is because they want you to get back to the target pressure. That seems to be the standard practice for most, if not all, car manufacturers. We have 4 different brands of vehicles at our house with TPMS and all are like that.

 

[04fxdwgi]

Heck, the premium display even states to pump up to 39 PSI (40-41 if you want to make sure its at 39 or above).

I bought the Autel TPMS 501 Pro tester and come to find out, the full size spare does have a sensor in it (mine is testing bad), but if the pressure in it is low, it will NOT alarm, unless the tire is mounted. If in the stored position under the bed, it WILL set off the light if sensor is bad, though, with no other dash indication saying what it is. Just the solid on light after blinking for 75 seconds..

I ordered new sensor and will install after receiving and verify if this is what my problem with the light being on.

 

[04fxdwgi]

Update:

To test my theory:
1. Using AlfaOBD, went into Car Configuration and found "Full Size Spare Present" and showed Yes.
2. Changed full size spare present from YES to "NO"
3. Went into RFHub and got the PIN number
4. Went to Reset RFHub, entered the PIN and did reset.

The TPMS light is now off. WOOHOO.. Definitely the spare tire is causing the TPMS light problem.

When I get the new TPMS sensor, will switch back to yes, then reset to see if TPMS light comes back on. I bet Yes. Will replace sensor, reprogram TPMS system with the tool and see if it goes away again, Bet it will.

 

[Jebb]

I was going to say the same thing. If you have always got the alert at around 32 psi the target pressure was probably still 39 psi.
To the OP, after you pumped up the tires and drove 10 miles did the alert turn off and then only reset the next day? Or did the alert never turn off? One thing I have found is that the vehicle display rounds everything up. Meaning if you only put 38.5 PSI in the tires the screen rounds up to 39 PSI, but the BCM (computer) is only reading 38.5 and not the full 39 that is required......at least I believe that has happened to me a few times in the past. I've gone back and put just a little bit more air in the tires and they reset.
As another post stated, if the target pressure is 39 psi and the alert doesn't trigger to 32 psi.......once that alert is set you have to pump the tires all the way up to the target pressure to reset the light. Just going back up above the low limit, like 33 psi, does not reset the light. This is because they want you to get back to the target pressure. That seems to be the standard practice for most, if not all, car manufacturers. We have 4 different brands of vehicles at our house with TPMS and all are like that.

That is not how it worked here in the past. Any time my tires got to 32 or so the tire light and chime came on. Upon raising them back up the 35 the light and chime went OFF. I did not raise them to 39+ psi EVER. It worked that way for YEARS and that's why it's what I always assumed it was supposed to be 35. Now the indicator only clears at 39 or more.

So, IMO, something changed. It is still my belief that the custom shop at my dealership reprogrammed the settings for these dealer-installed oversize tires and disconnecting the battery - or something else - somehow erased it. The shop is not there any more so I can't ask.

 

[Jebb]

Update:

To test my theory:
1. Using AlfaOBD, went into Car Configuration and found "Full Size Spare Present" and showed Yes.
2. Changed full size spare present from YES to "NO"
3. Went into RFHub and got the PIN number
4. Went to Reset RFHub, entered the PIN and did reset.

The TPMS light is now off. WOOHOO.. Definitely the spare tire is causing the TPMS light problem.

When I get the new TPMS sensor, will switch back to yes, then reset to see if TPMS light comes back on. I bet Yes. Will replace sensor, reprogram TPMS system with the tool and see if it goes away again, Bet it will.

So you think the light can be being triggered by a low SPARE tire? I thought the TPMS sensors were read by pickups in the wheel hub/brake assemblies. Didn't know they were "RF". Will check my spare...

 

[04fxdwgi]

So you think the light can be being triggered by a low SPARE tire? I thought the TPMS sensors were read by pickups in the wheel hub/brake assemblies. Didn't know they were "RF". Will check my spare...

Spare low pressure will NOT trigger the light unless the spare is mounted on an axle and driven.

It will trigger the light while in the spare cradle under the bed IF the TPMS sensor goes dead.

Just proved it...

 

[04fxdwgi]

That is not how it worked here in the past. Any time my tires got to 32 or so the tire light and chime came on. Upon raising them back up the 35 the light and chime went OFF. I did not raise them to 39+ psi EVER. It worked that way for YEARS and that's why it's what I always assumed it was supposed to be 35. Now the indicator only clears at 39 or more.

So, IMO, something changed. It is still my belief that the custom shop at my dealership reprogrammed the settings for these dealer-installed oversize tires and disconnecting the battery - or something else - somehow erased it. The shop is not there any more so I can't ask.

Mine hasn't been changed in the 3 years I have owned it, even after replacing my battery. Always been that way.

 

[Jebb]

Spare low pressure will NOT trigger the light unless the spare is mounted on an axle and driven.

It will trigger the light while in the spare cradle under the bed IF the TPMS sensor goes dead.

Just proved it...

Not sure this makes sense. What if there is no spare? How does it "know" the difference between a dead TPMS sensor vs. NO spare? AFAIK, the tire/wheel has to be on an axle for the computer to read it. If you've seen (proven) otherwise maybe it's a coincidence? On the other hand, if the system detects that the spare is flat or dead that WOULD be a good thing - but where would it show it, ie., should be a 5th tire in the display? IDK

 

[RamDiver]

Not sure this makes sense. What if there is no spare? How does it "know" the difference between a dead TPMS sensor vs. NO spare? AFAIK, the tire/wheel has to be on an axle for the computer to read it. If you've seen (proven) otherwise maybe it's a coincidence? On the other hand, if the system detects that the spare is flat or dead that WOULD be a good thing - but where would it show it, ie., should be a 5th tire in the display? IDK

Read post #12.

.

 

[Wild one]

Reading the spare must be something they implemented after 14,as my trucks spare has been in my shed since the truck was brand new.
Anybody looking for a brand new temporary spare in the Calgary area can have mine for a box of Pepsi,if they want to come get it

 

[04fxdwgi]

OK, new sensor came in yesterday. Went into AlfaOBD and reset car config to "Full Size Spare Present : YES". Went to RF Hub and reset. Powered off truck and turned on ignition. TPMS light back on.

Broke spare tire down and installed new sensor. Programmed sensor with TPMS tool and updated the truck with the tool through the OBD port.

Reset the RF Hub again, since there is a new sensor.

Voila, the light is now gone.

Let air out of spare and it DID NOT set off the light. Removed spare from truck and moved spare way out of garage. Tuned ignition on, now TPMS light blinks for 75 seconds (searching for the spare sensor). TPMS light goes on solid after the 75 seconds. Remounted spare in truck and verified 39 PSI air and TPMS light is now off.

All is good now and works as manual showed.