Accuracy of In-Dash Tire Pressure Monitor?

[marka5083]

I wonder if others have experienced a discrepancy between the in-dash tire pressure monitor and actual tire pressures. I find that the monitor is consistently off by 3-5 PSI even after resetting the monitor several times. However, it may be that this is within normal operating parameters as the monitor may not be designed to be precise, but to only be a backup/failsafe to accurate manual monitoring. Would be interested in other opinions. Thanks.

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[Dooty]

2011 BlueTec. I've filled the tires to recommendations. Shortly after leaving the garage, 3 are the same as the tire gauge. One is always one pound low. Pressure builds quickly after one mile but the readings are consistent. I think mine is very accurate!

[peeta123]

i cant even get a reading in my car

it just says that the tire pressure is ok

[RSIKR]

Originally Posted by marka5083

I wonder if others have experienced a discrepancy between the in-dash tire pressure monitor and actual tire pressures.

I find that the monitor is consistently off by 3-5 PSI even after resetting the monitor several times.

However, it may be that this is within normal operating parameters as the monitor may not be designed to be precise, but to only be a backup/failsafe to accurate manual monitoring.

Would be interested in other opinions.

Thanks.

If you adjust the tire pressure you have to drive the car for a while before the TPMS can read the pressure. By this time the pressure can increase from heat, both from the outside temperature, brake friction, flexing of tires etc.

Another consideration is the accuracy of your tire gauge. Some of the old style pencil gauges can be questionable. A good dial or digital gauge is an asset. When the TPMS achieves a reading stop the car and compare it to your accurate gauge.

I believe my TPMS is very accurate.

[hyperion667]

I think mine is accurate too......and it's less than a mile for the numbers to display....

[BenzMan369]

Some additional info:

While the TPMS should provide a reasonably accurate reading of actual tire pressures, it's my understanding that's not its primary function. It exists to warn you of a significant drop in tire pressure - based upon the "normal" tire pressures you have set it for.

If you adjust your tire pressures, you must do a TPMS Reset immediately thereafter. When the tires heat up with driving, the TPMS will then use the Reset values as "normal" to evaluate any significant drop. If you don't do a Reset, the warning system will be inaccurate.

Further, the TPMS system is calibrated to be accurate at sea level. If you live in a high altitude location, the system again may not be accurate.

MB recommends not relying on the TPMS alone for accurate pressure readings. They should be verified with a reliable manual gauge.

As RSIKR notes, many things can affect pressures. I have found that persistent driving with the sun beating down on one side of the car on a hot day raises the pressures on that side in comparison to the other.

[BenzMan369]

That is one gorgeous hunk of metal Hyperion!

Happy motoring.

[dfordham]

Originally Posted by BenzMan369

Further, the TPMS system is calibrated to be accurate at sea level. If you live in a high altitude location, the system again may not be accurate.

I live in southern New Mexico at almost 4,000 ft. elevation. I just used my TPMS for the first time this morning (just got the car) and it is within 1 psi of my tire gauge. So it seems that elevation doesn't have much effect, at least the elevations where most people live and drive.

Don

[MBTAZ]

I checked & reset my Complete TPMS (factory SDS, TPMS tool & certified Tire Pressure Gauge) at sea level & 68 f found 1 PSI off..
If your not using a certified tire pressure gauge you can be off even more..
As previously stated & MB / US law it's for safety not accuracy almost like depending on your outside temperature display for accuracy when it's only to check for frozen temperature & ice..

[RSIKR]

The TPMS is a great investigative tool. For example you hit the edge of a pothole, concerned about a pressure loss, check the TPMS before the low pressure warning alerts you. The most important factor is consistency. If there is a substantial difference from right to left side after they were inflated to the same pressure I would be concerned. As discussed the pressure increases when you drive and is related to ambient temperature. As BenzMan 369 pointed out, the sunny side of the car on a hot day can be a pound or two higher.

[YYZ-E55]

Originally Posted by peeta123

i cant even get a reading in my car

it just says that the tire pressure is ok

Most Canadian MBs use a passive tire pressure monitoring system (code 477) which uses the wheel speed sensors to determine if a tire is low. A low tire means increased rolling resistance, which is interpreted by the wheel speed sensor.

The active system (code 475) is mandated in USA and has a wireless pressure sensor in each wheel (as part of the valve stem). This is why you don't see an actual pressure value displayed in the instrument cluster.

[rovermark]

Originally Posted by YYZ-E55

Most Canadian MBs use a passive tire pressure monitoring system (code 477) which uses the wheel speed sensors to determine if a tire is low. The active system (code 475) is mandated in USA and has a wireless sensor in each wheel. This is why you don't see an actual pressure value.

YYZ-E55:

It says that it is monitoring Run Flat tires, but as far as I know, Canadian models are not equipped with Run Flats. Correct?

Also, if I change a tire myself (lets say a flat tire), will I have to go back to the dealer to have the system readjusted? Does it work through a remote wireless sensor in the wheel?

Thanks

[YYZ-E55]

Originally Posted by rovermark

It says that it is monitoring Run Flat tires, but as far as I know, Canadian models are not equipped with Run Flats. Correct?

None of the Canadian 212 E's have run-flats installed from the factory. I'm not sure where it indicates the tires are run-flat?

Originally Posted by rovermark

Also, if I change a tire myself (lets say a flat tire), will I have to go back to the dealer to have the system readjusted? Does it work through a remote wireless sensor in the wheel?

You do not need to visit the dealer. You can reset the system from the instrument cluster and it will re-calibrate automatically. There is no sensor in the wheel on Canadian models.

[EmE247]

Originally Posted by RSIKR

The TPMS is a great investigative tool. For example you hit the edge of a pothole, concerned about a pressure loss, check the TPMS before the low pressure warning alerts you. The most important factor is consistency. If there is a substantial difference from right to left side after they were inflated to the same pressure I would be concerned. As discussed the pressure increases when you drive and is related to ambient temperature. As BenzMan 369 pointed out, the sunny side of the car on a hot day can be a pound or two higher.

My TPMS monitor is on at all times in my car. Because of the crappy potholes + 19's/less rubber + somewhat crappy suspension in the W212, it's the first thing I look at when something doesn't feel right.

Not really sure what other functions might be useful in its place anyways. Need 2 read da manual someday.

[rovermark]

Originally Posted by YYZ-E55

None of the Canadian 212 E's have run-flats installed from the factory. I'm not sure where it indicates the tires are run-flat?

The message when checking the gauge screen states "Run Flat Indicator Active" (the same gauge that shows you the car info and allows you to reset it).

[YYZ-E55]

Originally Posted by rovermark

The message when checking the gauge screen states "Run Flat Indicator Active" (the same gauge that shows you the car info and allows you to reset it).

Ahhh - yes, as in "flat tire indicator". Good old genglish

[peeta123]

thats a good thing since i dont have to deal with the sensor batteries later

[Live Oak]

Originally Posted by peeta123

thats a good thing since i dont have to deal with the sensor batteries later

Sensor batteries?? I thought they were powered by the motion of the wheels.

????????????????

[marka5083]

OK, so after purchasing a better air pressure gauge, it turns out the the TPMS is very accurate. Those gas station gauges are for s#$t as well, I have learned. From now on I'll trust the MB and my better gauge.

On a different note, just drove ~350 miles on the highway between southern and northern CA and I have to say, driving the E350 really brings a sense of pleasure to driving long distances. Wow.

[K-A]

Indeed, this car is the king of long distances. It's truly an art! I've driven many long distance miles in this baby and I couldn't think of a better car engineered for such drives.

[220S]

Originally Posted by K-A

Indeed, this car is the king of long distances. It's truly an art! I've driven many long distance miles in this baby and I couldn't think of a better car engineered for such drives.

Seriously? There's no better car out there engineered for long distance driving? The E Class is the only one?

[El Cid]

Mine is about a pound different from tire gauge I use. Sometimes, some tires will match gauge and a couple won't. Have two gauges and they usually match each other. Interestingly, if leave TPMS on, TP's will change more in some tires than others and then maybe be same for all four again later.

[K-A]

Originally Posted by 220S

Seriously? There's no better car out there engineered for long distance driving? The E Class is the only one?

Where did I say that it's the only one? Lol. All I'm saying is that this car is engineered for long distance drives, and I can't really think of many that I'd rather be in on said long distance drives. This is taking into account safety, comfort, stability, interior ambiance, features, etc., etc.

[220S]

Originally Posted by K-A

Indeed, this car is the king of long distances. It's truly an art! I've driven many long distance miles in this baby and I couldn't think of a better car engineered for such drives.

"...and I couldn't think of a better car...."

Originally Posted by K-A

Where did I say that it's the only one? Lol. All I'm saying is that this car is engineered for long distance drives, and I can't really think of many that I'd rather be in on said long distance drives. This is taking into account safety, comfort, stability, interior ambiance, features, etc., etc.

"...and I can't really think of many that I'd rather be in......"

That's better. Sometimes I think you're getting too drunk off the MB KoolAid, so I have to step in to keep you in line once in a while.

[hyperion667]

haha!