TPMS sensitivity

[MikeM.]

The biggest reason for nitrogen on street cars (excluding track/race cars) is because compressed air has moisture which increases the chance of rotting on the inside surface of the tire and wheel.

The biggest issue with high humidity in the tire is that moisture laden air has a much higher rate of expansion than dry nitrogen. Dry air will work almost as well as dry nitrogen. The problem is that many compressors are poorly maintained and will fill your tires with too much moisture.

This is another factor that could cause a false TPMS alert. Say one of your tires was topped up with a compressor that had condensed water in the fill hose and the other tires have relatively dry air. When the vehicle is driven the moisture laden tire will increase in pressure substantially more than the tires filled with dry air and cause a TPMS alert.

Sometimes it's necessary to put on a thinking cap to figure out what your car is telling you.

 

[iced_theater]

I've never had my TPMS light come on and I've adjusted pressures down to 32 psi up to 45 psi, rotated tires, and different pressures front and rear.

 

[Chas]

Interestingly, and this may have been posted before, all other cars I had been familiar with that had the 2009 mandatory TPMS system uses direct pressure monitoring sensors...the valve stem is connected to a battery powered pressure monitor that sends telemetry to the car. The TPMS is tripped when the pressures go below a pre-programmed threshold, generally 25% below the pressure recommended on the driver side door frame.

The Mazda CX-5 is the first new car I have come across that uses indirect tire pressure sensing. It has the advantage that you can set the minimum thresholds. It has the disadvantage that you cannot take real time readings of the tire pressure (which is really kind of useless) that shows you starting out in the morning at 34/32 FR climbing 37/35 when the tires get hot.

The CX-5 manual says:

"The system monitors the tire pressures indirectly using the data sent from the ABS wheel speed sensors, which explains the manual reset procedure discussed above."

 

[MikeM.]

The Mazda CX-5 is the first new car I have come across that uses indirect tire pressure sensing.

The indirect method is becoming much more common recently and plenty of newer models have it. It has the advantages of using existing hardware (ABS, stability and traction control wheel speed sensors), doesn't add extra weight or batteries inside the tires and doesn't require the owner to purchase additional hardware if they choose to run winter wheels (just press a button on the dash and it learns the new tires/wheels).

Even with systems that measure the actual pressure it is best to set the pressures manually using one pressure gauge instead of assuming that all four pressure gauges inside the wheels are calibrated identically (and their accuracies have drifted by the same amount over time). Point being that I agree, it's mostly useless to have the individual pressures reported instead of simply being alerted when there is a problem.

 

[CX-SV]

The Mazda CX-5 is the first new car I have come across that uses indirect tire pressure sensing. It has the advantage that you can set the minimum thresholds. It has the disadvantage that you cannot take real time readings of the tire pressure (which is really kind of useless) that shows you starting out in the morning at 34/32 FR climbing 37/35 when the tires get hot.

The CX-5 manual says:

"The system monitors the tire pressures indirectly using the data sent from the ABS wheel speed sensors, which explains the manual reset procedure discussed above."

Yes, I had a 2006 Mercedes ML350 with similar TPMS system.

 

[sxa]

I have noticed that the TPMS will go off during normal fluctuations in pressure due to temperature/altitude. For example, a few weeks ago I drove up to Heber, AZ and the tire light came on, I checked my pressure and considering that I was at 7,000 feet the small change in pressure was to be expected, I left it as it was and checked the tires when I got back from the mountains after they cooled and they were fine.

 

[alex1706]

Mine has flagged up today, says Service Attention Required, I have a drop in Tyre pressure. What it fails to tell me though is which tyre.

So, with an electronic pressure gauge I checked all 4. Front, both are at 34 psi & rear were both at 44 psi. Where am I supposed to go with that?

Out comes my compressor (not the one as supplied by Mazda) and I top up all four by 2 pounds and double check the readings, then I followed to the letter the regime regards the resetting of the sensors. Made no difference at all! Still shows a warning that I need to deal with a low tyre pressure situation.

I then took it one stage further & put in another 2 pounds per tyre. Looking at the label in the door-shut I'm supposed to have 33 pounds per wheel if max 3 occupants, or 44 if 5 occupants. This top-up gave me 38 front, and 46 rear, No Difference! Even after following the re-set procedure as per the owners manual, still tells me I have an issue and one tyre is under-inflated.

Short of making them like balloons I'm at a loss as to what I am supposed to do. Looks like I'll be ignoring it all.

Unless anyone knows what else I can do?

Alex

 

[milrtime83]

Mine has flagged up today, says Service Attention Required, I have a drop in Tyre pressure. What it fails to tell me though is which tyre.

So, with an electronic pressure gauge I checked all 4. Front, both are at 34 psi & rear were both at 44 psi. Where am I supposed to go with that?

Out comes my compressor (not the one as supplied by Mazda) and I top up all four by 2 pounds and double check the readings, then I followed to the letter the regime regards the resetting of the sensors. Made no difference at all! Still shows a warning that I need to deal with a low tyre pressure situation.

I then took it one stage further & put in another 2 pounds per tyre. Looking at the label in the door-shut I'm supposed to have 33 pounds per wheel if max 3 occupants, or 44 if 5 occupants. This top-up gave me 38 front, and 46 rear, No Difference! Even after following the re-set procedure as per the owners manual, still tells me I have an issue and one tyre is under-inflated.

Short of making them like balloons I'm at a loss as to what I am supposed to do. Looks like I'll be ignoring it all.

Unless anyone knows what else I can do?

Alex

Why are you adding air to all of them if 2 are already 10psi higher than the other 2? Get them all to the same pressure, reset the TPMS and see what happens.

 

[Chas]

Mine has flagged up today, says Service Attention Required, I have a drop in Tyre pressure. What it fails to tell me though is which tyre.

So, with an electronic pressure gauge I checked all 4. Front, both are at 34 psi & rear were both at 44 psi. Where am I supposed to go with that?

Out comes my compressor (not the one as supplied by Mazda) and I top up all four by 2 pounds and double check the readings, then I followed to the letter the regime regards the resetting of the sensors. Made no difference at all! Still shows a warning that I need to deal with a low tyre pressure situation.

I then took it one stage further & put in another 2 pounds per tyre. Looking at the label in the door-shut I'm supposed to have 33 pounds per wheel if max 3 occupants, or 44 if 5 occupants. This top-up gave me 38 front, and 46 rear, No Difference! Even after following the re-set procedure as per the owners manual, still tells me I have an issue and one tyre is under-inflated.

Short of making them like balloons I'm at a loss as to what I am supposed to do. Looks like I'll be ignoring it all.

Unless anyone knows what else I can do?

Alex

Don't know what the tire pressure calls for in your market, but in the US, the label says 34 F and 34 R (17" tires). Based on how the indirect TPMS system works, the differential you describe of 38F and 46R would be enough to set off the system since it measures the difference in rotation speed between all four wheels. The two fronts would be rotating differently enough from the rears to set it off.

 

[alex1706]

Don't know what the tire pressure calls for in your market, but in the US, the label says 34 F and 34 R (17" tires). Based on how the indirect TPMS system works, the differential you describe of 38F and 46R would be enough to set off the system since it measures the difference in rotation speed between all four wheels. The two fronts would be rotating differently enough from the rears to set it off.

Thanks for your answers guys, you sent me off with a different perspective. Rotation speeds between rear/front made sense, yet I couldn't clear the message even before I had moved the car, so ruled that one out I suspect.

Dropped the rear ones to 2 pounds above the front tyre pressures, no difference, then made them all 36-psi, still had the message.

Went into "info" and seems like there is a period where it suggests you check tyre pressures, didn't tell me that in the manual though. So I advanced that to 6 months from now, then carried out the initiation/reset as appropriate. So far seems to be OK.

Alex

 

[CX-5-2013]

It would surprise me that the circumference of the tire varies much if at all with 3 or 4 pounds of pressure. It is not like the tire will stretch like a balloon
If it is that sensitive the load in the car would have an effect on the TPM also.
The distant around the tire must be pretty constant or the speedometer would be inaccurate.

My TPM goes off every couple months. Pressure is less than 2 lbs different.
If the tires lose air at the same speed the monitor would not indicate a problem.