Piston Slap: Indirect Answers on Direct TPMS Questions

Hagerty Community Member DUB6 writes:

Dear Sajeev,

I have three vehicles with a tire pressure monitoring system (TPMS) as standard equipment. All three (2002, 2004, and 2008 models) have the dash light on all the time, regardless of actual tire pressures. I know that the sending units are battery-powered and that they can be changed out, but I have several reasons to not do that.

1. I never trusted when the light came on even when the vehicles were new—often I’d turn the car off and back on again and the light would go out, and of course, cold tires sometimes caused a light that would go out in a mile or two as they warmed up. Other times, I’d actually check the pressure with very accurate gauges and find that the light was lying to me!
2. It’s a bit expensive to have a tire shop dismount all the tires, replace batteries, and then remount and balance everything just to give what I consider to be an unreliable system new life. And honestly, I had a tire guy tell me that about half of the sensors that they try to re-power are faulty and it isn’t the battery at issue anyway.
3. Since I’m diligent at checking my pressures, it just seems to me to be a waste anyway—I really think I know more about my tire pressures than TPMS does.

So the question is: Can I disconnect the TPM Systems and do away with the light altogether?

Yes, I know, put a piece of electrician’s tape over it, right? But seriously, can/should it be done?

Sajeev answers:

Before we proceed, let’s level-set on the two different types of TPMS designs out there on the roads. The first is what you are discussing, with a sensor mounted inside the wheel (or within the valve stem). That’s called a Direct TPMS system, but there’s also an Indirect TPMS system that utilizes a vehicle’s ABS brakes to see if one wheel is spinning faster because of a decrease in circumference.

The Indirect TPMS system is less accurate, as it does not measure air pressure inside the tire: It cannot spot an issue if all four tires lose air at the same time, like when there’s a rapid decrease in outside temperature. But this setup is better for long-term ownership, because there are fewer parts to maintain, and there will be less E-waste to wind up in a landfill.

So let’s actually answer your question, as you likely have a Direct TPMS. You need to pick one of the following:

1. Spend $200-500 on replacement wheel sensors, programming, and tire removal/installation.
2. Put a “piece of electrician’s tape over it” as you wisely suggested.
3. Try some form of wiring harness mod to the TPMS to trick the system into thinking everything is working correctly. If I found this particular hack for Toyota products, odds are others have figured out a decent hack for your application.
4. Theoretically, the TPMS system is controlled by a modern vehicle’s Body Control Module (BCM), so finding a shop that re-programs BCMs might be in your best interest. It might be the same or more money than just replacing the sensors, but it will be a permanent fix. It never hurts to find these shops with an Internet search and drop them a line!

For those with Indirect TPMS, I recommend you do nothing aside from cleaning the ABS wheel sensor/tone ring at each corner. But if you have battery-powered, Direct TPMS, look around locally and find a tire shop to install new sensors at the lowest price. I recommend cross-shopping the big-name tire stores against independent shops in areas where the big guys fear to reside. Full-on replacement still requires legit sums of money, and it’s far from a one-time expense. (Remember that tire sensors often have a 10-year lifespan.) You can save a few dollars by avoiding a dismount/remount if you perform the TPMS install when you need new tires.

And the merit in replacing these sensors depends on each individual case. It often depends on the passion/performance/complexity associated with the vehicle (is it a 2006 Porsche 911 Turbo, or a 2006 Dodge Caliber?), the zip code where it resides (a growing area with a lot of construction and/or poor quality roads?) and the level of interest from its current owner.

Electrical tape is cheap, and wiring harnesses aren’t necessarily scary. The only wrong answer here is not keeping an eye on your tire pressure, be it with a gauge or within your gauge cluster. What say you, Hagerty Community?

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