Everything you need to know about TPMS for the C5

Through little to no fault of my own, over the past decade I’ve either adopted or purchased several vehicles that were equipped with modern, legislated TPMS. As such, being a die-hard do-it-yourselfer, the technology has necessarily become quite familiar to me.

It wasn’t until I recently acquired a C5 that I would realize how many more vehicle owners the technology effected, for good or bad. To this end I’ve set out to share what I’ve learned so as to hopefully help someone suffering from the dreaded “service tire monitor” light.

In a (quite protracted and complex) nutshell, here’s what you need to know about TPMS for the C5 Corvette (subsequent generations are very similar). For the record, when I decided to finish this document for posting on the forum I consulted one of the moderators who shall remain nameless. His advice was to include as many pictures as possible. I chose to ignore his advice, because pictures are too specific. I’m not here to endorse any specific brand or type of sensor but to educate you on the technology so you can make educated purchases and decisions. While a picture can be worth a thousand words, sometimes the knowledge gained from reading a thousand words can arm you with the priceless talent of being able to ask the right questions. I promise, I’ll make it as short as possible. Alternatively, if you “need” an answer in less than 5 minutes you’d better go to YouTube and prepare to be disappointed.

Assuming you havent defected to YouTube - as I’m sure you’re at least vaguely aware, the technology consists of a set of transmitters connected to the tire valve stem that directly measure the tire’s internal pressure and transmit this telemetry periodically. On the other end of the transaction, the RFA module receives and decodes this telemetry data and sends it along to the BCM so that the driver can press the ‘gauges’ button on their DIC interface and see the pressures for each of the four tires while sitting still or blasting down the road at speed. Wonderful, until it stops working…

To skip the excruciating details of how the system works, here are the important parts.

Part 1 - Receiver Module

The RFA or remote function adapter module in the C5 is responsible for receiving telemetry packets from the four tires sensors, keeping track of the sensor’s learned unique identifiers, as well as performing similar tasks for the vehicle’s remote entry fobs. When data is received from any of these inputs it then transmits data on the class 2 serial bus (aka ALDL) to other modules.

I’ll try to come back and provide some part numbers, but to summarize the early model C5 RFA modules were configured to accept a certain frequency and encoding of data. I can’t elaborate on the keyfob side of things as I’ve little knowledge here, but on the TPMS side of things, the domestic RFA modules for the 97-00 Corvettes were configured to decode transmissions on 315mhz using ASK or amplitude shift keying modulation. This modulation would be synonymous with how AM broadcast radio modulates the analog audio signal. Starting with 01, the remaining model years of the C5 switched to FSK or frequency shift keying modulation, also on the 315mhz center frequency. It should surprise no-one that FSK modulation is likewise synonymous with FM broadcast radio where changes in frequency around a center frequency is used to modulate / encode the analog (in our case digital) signal.

This all may sound extremely complicated, and at the technical level it is. But for those of us just wanting to make the ‘service tire monitor’ warning go away, it doesn’t need to be!

“Domestic” Disclaimer:

If you took notice of the word “domestic” in the 2nd previous paragraph, here’s its relevance. In most production years, GM produced a substantial number of C5s that were destined for export to foreign markets. I’m not entirely clear on all the details, but one of importance to us is that at the time 315mhz was a regulated frequency in Europe, and possibly Japan, and those vehicles would have been equipped with RFA modules set to receive TPMS telemetry on the 433mhz frequency, as well as being equipped with similarly capable tire sensors. This detail becomes important if you’re trying to replace sensors in a car that was built for export to these markets, as the North American 315mhz sensors simply won’t get you anywhere.

RFA Module Swaps

I’ll go into detail about sensors later in another topic. But while we’re discussing the RFA module it would be wise to bring up the subject of module swaps– as the older ASK modulation sensors and key fobs began to become more difficult (and expensive) to source, some owners opted to swap the RFA module from a 01-04 C5 into their early model C5. One would have to research the part #s further to be certain, but this is something to consider if you’re working on a vehicle with an unknown past. As I’m writing this article in March of 2024, the last C5 rolled off the assembly line no less than 19 years and 10 months ago. If the “car facts” report on your C5 shows more than 2 owners, you can bet there’ve been a boatload of modifications (both good an bad) performed on your car, not all of which will be readily apparent without extensive disassembly and research. Just something to consider…

Part 2 – Programming, Training or Relearn – WTF?

Let’s clear up the differences.

Training / Relearn

Overwhelmingly in the context of replacing sensors, we will be training or relearning. The process by which this happens can be initiated from the DIC with the following (condensed) sequence:

1) with key on, engine off clear any DIC messages with the ‘reset’ button
2) press the ‘options’ button repeatedly until the DIC display goes blank
3) press and hold the ‘reset’ button until ‘FOB TRAINING’ diplays on the DIC
4) press the ‘options’ button again until ‘TIRE TRAINING’ displays on the DIC
5) press the ‘reset’ button – if vehicle is so equipped / configured ‘LEARN L FRONT TIRE’ will display along with the horn sounding
6) trigger the sensor in each tire with a suitable trigger device in a clockwise manner… (yada yada)
7) the horn honks twice signaling the process is complete

Sensor relearn can also be initiated by a scan tool via the class 2 serial bus (aka ALDL) with a device such as a Tech 2 or similar.

Both scenarios trigger the same condition. What’s important is what happens next.

Once the RFA module receives the proper sequence of instructions from the class 2 serial bus, it switches into relearn mode. This can be for a new / replacement / additional key fob, or a new set of tire sensors or a new arrangement of sensors (for instance after having rotated tire locations).

When the relearn mode requested is for tire sensors, the RFA is instructed to listen for transmissions from tire sensors on it’s allocated frequency, modulation and encoding configuration. When it decodes a valid unique transmission it hasn’t already heard during the current relearn session, it assigns that sensor’s unique identifier to a location in RAM (temporary memory) in the order of driver’s front, passenger’s front, passenger’s rear, and finally driver’s rear. Each time a location is “learned” it sends a message to the BCM to honk the horn to alert the user that a valid sensor was learned, and to move to the next location. When all four locations have been relearned it stores the sensor identifiers semi-permanently in eeprom and instructs the BCM to honk the horn twice to signify a successful relearning sequence.

This may be the most important bit of information to take in here - during the relearn sequence the technician (you) must somehow instruct the sensors attached to the valve stems to wake up and transmit their telemetry packet.

How this is done is fairly inconsequential, but in my observations it has become apparent that the prevailing wisdom is that for all C5 Corvettes this must be initiated by placing a magnet in close proximity to the tire pressure sensor. This assumption is completely inaccurate, and depends entirely on what type of sensor is installed in each wheel (the subtext here is there are four, and there could be several different types of sensors installed at each location).

You might ask, how do I know what type of sensors are installed? The answer is you can either find out via trial-and-error, have the tire beads broken down and inspect the sensors, or you can do what I would strongly recommend for a vehicle this old and simply have them all replaced with sensors of known origin and compatibility.

Programming

Unfortunately, a lot of online documentation incorrectly refers to the process of training / relearning as “programming”. To further complicate the matter, most modern sensors can be programmed with different configuration options, such as changing the unique ID, the type of telemetry data transmitted, and even the frequency and modulation techniques. In fact it is possible to purchase universal, programmable sensors that are shipped without any configuration which must be programmed with a configuration before they will do anything.

I could go on for several pages about programming, but instead will stick to what’s important to our scenario – programming method. Most programmable sensors are capable of being programmed wirelessly using the same 120khz signal that’s used to trigger them. Some however are also capable of being programmed in a cradle using physical electrical contacts that talk to the sensor’s processor over a serial protocol / UART (universal asychronous receiver / transmitter). These type of sensors are in my opinion highly preferable over ones only wirelessly programmable. The reason for this is because the programming device can also provide power to the sensor during programming, whereas the wireless variety must use power from the internal battery for said process. As these batteries are typically not easily replaced, this is detrimental because this programming process comes at the potential cost of several years worth of battery life to complete.

Part 3 – Trigger Sources

You might ask what causes a tire pressure sensor to wake up and transmit it’s telemetry data?

Early models such as the ones our cars were originally equipped with had two possible trigger sources. During normal driving conditions an inertia switch was responsible for triggering the sensor’s internal processor to wake and transmit it’s telemetry periodically. They were also equipped with a reed switch which is a type of switch that closes it’s contacts when in close proximity to a strong magnetic field.

As the technology evolved, sensors sometimes included logic and / or receivers that would wake the processor if the measured tire pressure changed rapidly, or if a low-frequency radio signal was received (typically 120khz).

As of 2024, almost all tire pressure sensors designed for current technology standards respond solely to the 120khz radio frequency signal and inertia. These120khz trigger devices are widely available from all the usual internet selling sites. A quick search for “tpms tool” on several of them show a device that looks entirely identical for as little as $3.00 and as much as $39.00. The colors and item descriptions may vary with manufacturer compatibility and nonsense like "2024 Edition" which may be confusing, but specific part #s such as "OEC-T5", "EL-50448" and "GL50448" all do the exact same thing. If all you're wanting is a simple trigger tool, pay no attention to your specific vehicle being listed in the compatibility matrix. The tool doesn't communicate with the car, it communicates only with the sensor. Also, anything more expensive will likely have other capabilities that are generally not needed for GM TPMS work.

You might ask “why do I need to know all this nonsense?”

If you’ve owned your C5 since new and have meticulously kept track of what tire pressure sensors have been installed in your wheels, then you probably don’t.

For most others, it’s safe to assume you have no idea what type of pressure sensors are installed in your wheels. As such it’s good to be educated on what the possibilities / requirements are to trigger any type of sensor, lest you end up having to take it to “the guy” and have the tires popped off the rims.

Part 4 - Sensors

Once again, just to be clear I’m not getting any kick-backs for recommending specific brands. I’ve just found what I like, and for me that’s whatever gets the job done with the least amount of hassle and as cheaply as humanly possible. If you don’t care what a set of sensors costs and want to have absolutely no involvement in the process of making them work, my advice to you is to take your car to whatever tire shop you prefer and ask them to replace and retrain the sensors while they’re changing the tires. Then hold them accountable for making them work. Incidentally, one of the motivating factors for my writing this up is because of stories of tire shops installing sensors they recommended, and then not being smart enough to know how to relearn them to the Corvette. Excuses ranged from “the guy that knows this stuff isn’t here today” to “it must me a Corvette specific thing”. I’m writing this to give you the means to call bullsh!t and I encourage you to do so liberally.

On the other side of the coin I personally prefer to know what I’m getting, how it works, and most importantly knowing I didn’t pay a 2.0 or 3.0 markup for the electronic device that was almost certainly manufactured on another continent along with most of the raw materials involved in said manufacturing.

Physical Varieties

Aside from compatibility details relevant to the digital telemetry data, there are generally two different types of physical sensor varieties – ones with clamp-in stems and ones with pop-in rubber stems. There is no real difference – most rims will accept either type. There are even some universal sensors that can be mounted on either type of valve stem. Unless I’m fighting with a problem getting one type of stem to seal in a particular (and usually old and corroded) rim, I simply prefer pop-in stems. My reasoning is they’re always simple to remove. Additionally, aluminum clamp-in stems can sometimes become difficult to remove after years of exposure to corrosive conditions that can cause the clamping nuts to seize to the stems and necessitate removal by drilling.

Technical Compatibility

From a practical standpoint there are generally just three important details – does the sensor transmit the correct telemetry data, on the correct frequency, using the correct modulation. Since that’s not something easily quantifiable without very expensive test equipment I’m going to spare you the technical details and reference some brands and part #s that I have personally tested, or have had other members verify performance for their C5. Once again, I’m not getting any compensation for this, it’s merely my personal experience in the quest to find the cheapest tire pressure sensors for a C5.

My personal #1 is the SmartSensor 17-43041 / 17-43042. These are available in 10 packs for around $23 per sensor. One version comes with clamp-in stems and the other pop-in. The sensors themselves can also be connected to either type of stem. The drawback to these is they are mainly sold un-configured (re-read the section on “programming”) and so require configuration with a semi-proprietary tool that is an additional expense. The reason I’m citing these as my “favorite” is because this one sensor accompanied by the programming tool will work for every car in my fleet. Both early and late model C5s are covered as well as newer models (the C7 is the newest my programming tool lists, though it hasn’t been updated in several years). These sensors are programmable wirelessly, or more importantly with the cradle included with the 17-144 tool package. Can only be triggered via 120khz tool.

My second favorite is the MoreSensor which seems to be exclusively sold pre-programmed through “the big A”. There seem to be numerous part #s depending on early / late and clamp-in versus pop-in stem configurations, and they seem to be very transient in availability. These seem to be by far the cheapest alternative as they were around $62 for a set of 4 when I purchased them for my 2001 back in 2020. Part #s are KX-S028-SN (early pop-in) / NX-S022-4 (late clamp-in) / NX-S022-SN-4 (late pop-in). Can only be triggered via 120khz tool.

Ranking third is the Schrader 29178 (early) / 29179 (late) clamp-in sensor. These are now available through the website that sells “all the parts your car will ever need” for around $22 each. These are in fact universal, programmable sensors that Schrader has finally discovered will sell more readily if they pre-program them for specific applications before bulk packaging. Update: thanks to member LannyL81 I had the opportunity to buy one of each for testing and believe they are as good or better than any O.E. style sensor still available for this application. Though the item description on said company’s website states “Magnet may be required to activate” this is once again patently incorrect information. Once again, these can only be triggered via 120khz tool.

Beyond #3 I can only give general advice. There are likely hundreds of different compatible options. What I would recommend over everything else is preferring sensors that have been freshly manufactured over new-old-stock, because the Li-MnO2 (litium ion manganese oxide) chemistry batteries they are equipped with have a finite shelf life. This necessarily eliminates all versions of the O.E. Schrader parts which were magnetically triggered as they have not been produced in well over 10 years.

Edit: One other general warning - beware of sensors found on eBay. It seems there's someone asking for help "programming" the sensors they bought on eBay every other month. Many never get them to work and end up buying something else.

Final Bits of Advice

This is the easiest part for me. If you’re buying sensors on your own and having them installed with (or without) a tire change...

1) Always, always, always attempt to learn the sensors to the car before having them installed. If they can’t be relearned by the RFA investigate the problem with the seller / vendor. I’ve personally never seen a sensor that could be triggered by either magnet or RF that wouldn’t transmit at atmospheric (0 psi).
2) Document what sensors you have purchased, and take a picture of them, preferably before having them installed!
3) Don’t assume the tire jockeys will know more about the technology than you do after reading this

Part 5 – Battery Replacement for Old Sensors

Short story, I’ve done it. Don’t bother. Period.

Longer version, there are numerous reasons not to waste your money and time (or someone else’s time and quite a bit more of your money). When I first started to frequent the C5 tech forum here I somewhat foolishly offered my services to another member wanting the batteries replaced in his O.E. sensors. Having lots of ambition and not wanting to do things half-assed, I bought a tray of batteries and the chemically “correct” two-part potting compound (incidentally this is not what “liquid electrical tape” is). I also went to the trouble of building a jig I could clamp to my workbench to hold the sensor steady while I “chiseled” the old potting compound out of the sensors. Here’s what I learned…

Of the eight sensors the member had me work on, only four were repairable with a battery replacement. Two had signs of internal chemical corrosion on the circuit board from the lithium-manganese batteries leaking after 15+ years of service (yes, they can leak just like alkaline batteries). One showed evidence of having been “beat to death” by the tire bead being incorrectly seated. The last one had an inertia switch that no longer produced a rattling sound when shaken, along with other evidence it had been contaminated with a can of fix-a-flat.

In summary, just don’t bother thinking about battery replacement as a viable option. Even if you’re showing your car at Amelia Island, there’s no way for the judges to know you have aftermarket tire sensors in your tires. Trust me, either have the TPMS function disabled, or go with new “chinese” sensors. It will be best for everyone...

 

Nice overview! Thx for putting this together.

 

I had the RR sensor replaced this past Wednesday on my 2020 Impala. Initially the RR set off the led and in my dic showed 2 dashes. The other three were ok. Using my relearn tool each of the 3 good sensors sounded the horn as it should but not the RR but this time ALL positions in the DIC showed dashes. Took it to the shop and learned as long as that RR sensor was bad, the relearn procedure was not able to complete the 4 sensor circuit. Replaced RR sensor and all is good,

 

That's the one drawback to the way the GM stuff works. I think Ford is similar.

On the other side of the spectrum are ones like Toyota where the only way to change sensor IDs is with dealer level diagnostic software.

 

Great right up for DIY'ers. I having new shoes put on along with other stuff and have new sensors that I will leave to my go-to #1 mechanic to install and get working.

 

Thanks, glad folks are reading it!

This offers a perfect opportunity for a quick Q & A. So it sounds like you've purchased your own sensors. If this is the case, have you followed my #1 piece of general advice in this case?

 

great writeup...should be a sticky

@Vetteman Jack

 

Very good write up. I have added a link to this thread in this already existing sticky https://www.corvetteforum.com/forums...3-19-18-a.html.

 

My TPMS haven't been working for 3-4 years. I now need new tires but have a hard time justifying spending an extra $300 to replace the TPMS. Will tire shops replace tires on a car without replacing non working TPMS?

 

Suggest calling the shop and ask them.

 

The reason I went to all the trouble of writing this was to arm people with information. If you read the first post you should have noticed that it's possible to buy an entire set of sensors and a trigger tool for less than $100.

Most tire shops will install sensors that you bring with you, but some won't. Though I find it somewhat pointless to have tires mounted without replacing the sensors when they're so cheap, I've never heard of a tire shop requiring the TPMS to be in working order. It's not even required on mandated vehicles (2008 and newer) in most states.

 

If you can get a TPMS for $25, then it will be a Chinese part and will last 3-4 years at most. Then you will be going through the TPMS headache all over again. I know, I've done it and got less than 4 years going the cheap route on my 2003. I have 2 Corvettes (2003 & 2009). Like MOST Corvette owners, these cars are not daily drivers and stay garaged most of the time. Bending down and periodically checking the tire pressure is no big inconvenience and in my trunk I carry a 12v air compressor in all my cars for when I need air or get a flat. I've driven most of my life (probably one million miles) without TPMS and don't see the need or desire to spend $200-$300 on something I never use. It's just "cool" and really not useful to me. Yes, I checked and Discount Tire will install tires without installing new TPMS. By the way, the TPMS in my 2009 is the original ACDelco and now 15 years old and still working --- clearly not a Chinese part.

 

Actually, the cheapest option I mentioned was a Schrader for $22. Are they chinese?

I respect what you're saying, but without knowing what type of sensors you bought (that only lasted < 4 years), you're generalizing an awful lot. I have a set of extremely cheap sensors ($22) in my beater commuter car that I installed in 2017 and they're still going strong. They've currently outlasted two sets of tires.

The sensors that were in my 'summer' rims when I got the C5 were completely dead. When I installed the current set of chinese sensors we found the previous tire shop installed universal Autel sensors that are only programmable wirelessly. As I mentioned, the flash procedure of programming a sensor wirelessly can use half the battery's life in a matter of 30 seconds.

Whatever the case, I'd rather have working sensors because if it saves one rim that makes up for the 'hassle' - not that I feel it is.

 

If you have access to a Tech2 you can turn off the TPMS.
This only works on the 01-04 cars

 

For some reason, when my car battery went dead and I replaced it, now I no longer get any message on my DIC telling me the TPMS are not working ---- so I don't need a TECH2 to kill that message which I used to get every time I started the car up and would have to hit the reset button. I'm happy to be without the TPMS headache on my 2003. TMPS is "COOL" but mostly worthless

 

Just the info I needed. The little amazon device did the trick first time around!

Thx!

 

Great write up. I installed the Schrader sensors on my 2000 about 9 years ago, which I purchased from O'Reilly's and had my chevy dealer install them when I purchased new wheels. I just received the Check Tire Monitoring System on the DIC because the front passenger side sensor apparently stopped working. I need new tires anyway, so I'll probably replace them with the same ones. Actually, after doing some shopping, I'm leaning towards the MoreSensor you mentioned in your post. They are $21.95 each with free prime shipping. Rock Auto has a Schrader sensor for the same price, plus shipping. The More sensor is manufactured in Taiwan and comes with a longer warranty.

 

Thanks for the.. I just replaced the RFA in my 2002 Z06 abs the new (used) unit had TPMS enabled giving me the "service tire monitor" (or something like that) warning each time I start. Is like to just add the sensors and make it useful (not sure how anyone can view tpms as not useful!?). I assume the tire has to be removed from the rim to install the sensor? How much of a pain is this? My tires are good with plenty of life left.

 

Edit: Disregard the next couple paragraphs, I was having a senior moment... :-)

A word of warning on these - as I mentioned in the first post they're shipped un-configured, so you'll either need to buy the 17-144 tool, or know someone who has one. There are other TPMS tools that can flash a configuration on these wirelessly, but only the 17-144 tool can do so while powering the sensor in it's cradle. I would be happy to flash a set, but then there's the postage to get them to you. :-\

As I mentioned, the only reason I like this sensor is b/c I have three other such equipped vehicles and this tool has paid for itself b/c I can configure the universal sensors for just about any vehicle equipped with TPMS. It's also helped me diagnose issues with learning sensors.

If you currently have clamp-in stems (fairly sure they were standard on all C5s), clamp-in sensors can be installed without completely removing the tires if you find a tire shop willing to do this. I've done it at home by breaking the outer bead and then using a quick-grip bar clamp on the tire. Just don't drop the sensor into the tire! I have to warn you that smashing the tread of the tire in this way can sometimes cause the belts to separate - especially with older tires or tires made with harder compounds.

That's an interesting tidbit you brought up - that the TMPS option is in the RFA. I don't have a Tech2 so have never messed with it, but prevailing wisdom seemed to indicate the option for TPMS was in the BCM, not the RFA.

 

I have no idea what type of stems they are. I have aftermarket wheels (Fikse FM10) in stock size. I have some curb rash on one, so maybe I'll get that repaired and these installed at the same time.


the only thing I can say about the RFA, is that my Z had all stock parts. Key fob quit working and wouldn't relearn. So I replaced the RFA with a used one (same part number as mine...10312535) . Fob now works and I get the "service tire monitor" message on start up.