I think I might have a bad tpms antenna. The right rear sensor will program ok, reads correctly for a bit and then drop off, triggering the dic to display an issue.

I've already replaced a new sensor with another new sensor, and have the same problem. I can reprogram it and its ok for a bit, but then drops off. I've also reassigned the sensors to verify, starting the relearn procedure at the right rear, which will then read as left front, and it will drop after some time driving. The sensors are good in my view, and the next cheapest place to look is the antenna for that side.

Does anyone know a good way to test the antenna?

eta: The car was last shutoff with the tpms error, and I just now unplugged and plugged the antenna back in. Viola! The sensor is back. It's only a short drive away from dropping off again....I hate electrical problems!

 

ummmm? So where was the "antenna'?

 

Behind the carpet, underneath the truck locking mechanism. I found a corvette salvage place that had antennas for 4.99 each. Cheap place to start I guess.

 

I don't believe that antenna is for the TPMS. My understanding is that it is used to verify a FOB in in the vicinity when the button to open the hatch is depressed. Since there doesn't appear to be a counterpart antenna near the front of the car for the front wheels, that tends to support that understanding.
Furthermore, if there were individual antennae for front and rear wheels, it would have been logical to have separate ones for each wheel and therefore eliminate the need to index the sensors in a specific order to match their locations to the DIC readout.

I'm guessing your act of unplugging and reconnecting that antenna, merely reset the DCDLR. To verify that, try unplugging it and operating the car. If you still get DIC pressure readings, you know it's not part of the TPMS. If you can't open the hatch with the button, you know it's just the antenna for the FOB.

 

Correct, but from what I've been seeing, its an antenna used for both key fobs and tpms sensors. There are 3 antennas (#4 in the diagram) that plug into a 315 MHz receiver module (gm25938511, #1 in the diagram) located in the dash.



Since its an intermittent problem, starting with replacing the antenna is the cheapest way to go. If its not the antenna, it the wiring for the antenna, or the channel in the receiver for the location affected. The receivers are expensive compared to an antenna replacement.

Does anyone have some info from the service manual?

 

There are actually 4 antennas that tie into the RCDLR. One for each door, one for the hatch, and one for the ignition switch. There are no other antennas tied to the RCDLR. Each of those antennas relay a low power signal from the FOB to the RCDLR in the same manner as a proximity switch. The RCDLR communicates directly with the tire sensors in the order that they were initially learned with a higher power signal.

I was basing my previous post from memory and asking you to confirm it by doing your own test. Since you still have concerns, I looked in my service manual, but there is no additional information regarding antennas than I've already mentioned.

The problem that you have is with an interruption in the signal between the RCDLR and that individual tire pressure sensor. It may be caused by a weak battery if the sensor has had a lot of time in service, and/or because of external RF interference. It's also possible that you have a non-OEM part blocking a direct signal. There are too many sources of interference to list, but the most common are cellphones and their chargers.

 

I'm on my second, or is it third or fourth new sensor? Whatever, 100% its not the sensor.

its always after an hour or so of driving that the problem occurs. GM should have built in a way to turn the stupid thing off so this wouldnt be a problem.

Spending $425 on a LG trackbox isn't the most inviting thing either.

 

After installing more than one new sensor and still having the same problem is an indication that you have an interference issue that you're not able to identify. Now it appears that rather than trying to find the source, you're willing to turn it off, which is actually simple.

Take one of your new sensors that has been in a wheel and worked correctly for at least more than 2 minutes, and relearn it to position 3 of the sequence while bypassing the right rear wheel. Then put it in a sealed chamber with a valve stem installed. Air up that chamber to 35 psi and you're done. You can put the chamber in the glovebox, under or behind the seat, or anywhere else in the car. The RCDRL will read that sensor and report the pressure as RR on the DIC. Of course, you'll have to manually check tire pressure in the RR, since that wheel sensor is no longer in the sequence. The reason for 35 psi, is that'll always be an odd number to show on the DIC, you'll be able to spot chamber leakage, and it won't set off a high or low pressure warning.
You can make the chamber from a section of white PVC pipe that the sensor will fit into and then glue on end caps. Be sure to drill and install a rubber valve stem (not the stem of the sensor) before you seal it.

 

No idea just one sensor would get interference. Would love to figure it out, but im afraid that would take more time an $ than its worth.

 

Rode around with no cell phone, an hour or so of driving, the one sensor drops off again. Any other ideas?

The only other non stock item I have in the car is is the Kawal aux in module.

At this point, its either replace the fob/tpms module or drop $425 on a LG track box.

 

I would check all of the ground connections near that area. I had a similar issue with one of my front sensors, and I shielded the 12V power wires to both outlets (under the center console) and it solved my problem.

Any loose connection can potentially cause RF interference, and it does not take much to mess with the C6 TPMS system.... That's why I would start with grounds first.

 

The antennas pictured in the diagram are the antennas used to signal the fob when attempting to open a door/trunk or start/stop the car.

The only receive antenna for the TPMS is part of RCDLR located in the dash above the radio. The TPMS sensors (and the fob, of course) send their signal to this antenna.

The RCDLR is not impervious to failure and there have been threads posted about replacement and disassembling the unit to re-solder some bad internal connections.

 

I'm thinking you should just spend the $425 so you can sleep at night.
It's far more expensive than the solution I offered, so according to some people it must be the superior method. It'll allow you the opportunity to manually check tire pressure on all 4 tires every morning instead of just one. If you happen to get a flat during the day, simply call AAA and wait for them to arrive.

Of course, a trial disconnect of the Kawal, costs nothing, so logically it can't possibly cause the problem.

One other solution that is cheap, is a piece of black tape placed over whatever light or DIC message annoys you the most.

A new RCDLR is in the $120-160 range plus $$$ ? installation, but has no guarantee to fix the problem, so you could be back to square one.

I hope you recognize the sarcasm, but they really are options.

 

I jinxed myself, I'm now getting it again on mine. I'll mess with it this weekend (check the TPMS voltages with my tool, check the grounds, make sure nothing is plugged in causing interference, etc.) and report back.

The only thing that changed was we had a torrential rain, and I SLOWLY ran thru about 6 inch deep water for about 100 feet, as I started my car in a parking spot to move to higher ground.

Could be coincidence, but will check all connections near the wheel well areas this weekend.....

Mine goes away after 2 or 3 car starts, and it eventually says "SERVICE TIRE MONITOR SYSTEM", even though it appears only only my left front is acting up.

 

To close out from my comment above, my latest TPMS issue appeared to be caused by me using my iPhone 6 with Waze near my radio area AC vents (I have a cell phone mount that clips into the CD slot).

Mine only acts up intermittently when doing this, so I'm assuming the cell interference is overpowering the RCDLR system (which is directly behind it).....

 

Thanks for posting the update.

I-Phones seem to be more problematic than androids when it comes to interfering with the C6's. Go figure.

I mount my LG phone near the same location as you and run Waze with no issues.

 

This information is incorrect. The antennas in question both send and receive signals. (taken directly from the factory service manual).

The introductory paragraph incorrectly states the RCDLR internal antenna is the only receive antenna. It goes on to incorrectly state that "Japan" is the only country with the remote mounted antennas. If you read further on in the break down of the complete system you'll discover that the four antennas both receive and send signals.

 

I'll stand by my interpretation of the Service Manual and testing using an RF Spectrum Analyzer.

 

Pretty hard to interpret this any other way. (From the 2006, 2007, and 2008 factory service manuals that I checked)

Keyless Entry Antennas
The keyless entry antennas are used to transmit and receive RF communication with the keyless entry transmitters when accessing the vehicles doors or rear compartment.

The antennas are controlled by the remote control door lock receiver (RCDLR). When an exterior door handle switch or exterior rear compartment lid release switch is pressed, the respective antenna sends out a challenge to the transmitter, which begins the passive entry communications.

The keyless entry antenna backup is located in the glove box area. It has a small pocket next to it where the key fob can be inserted if the key fobs battery is dead, weak or the radio frequency (RF) signal is being jammed.

The purpose of the keyless entry antenna backup is to send a low frequency RF challenge to a programmed key fob, inside the interior of the vehicle, when the start button is pressed. The keyless entry antenna backup is controlled by the RCDLR.

Also noted in this description of the fobs.

Keyless Entry Transmitters
The keyless entry transmitters are used to passively or actively lock and unlock the vehicle. When any one of the 4 allowable programmed key fobs are challenged by a keyless entry antenna by depressing either of the exterior door open switches, the transmitters will passively send an RF signal to the remote control door lock receiver (RCDLR) via the door antennas. The RCDLR will then interpret this communication and either allow entry into the vehicle, or deny it.

 

I re-visited my Service Manuals and found the description you quoted.

I stand corrected on the door opening sequence of events.

When we tested this stuff 10+ years ago, we shielded the RCDLR (and its' internal antenna) with a sheet of vinyl encapsulated lead and could not get the door to passively unlock.

The TPMS diagram description in the Manual shows only the RCDLR antenna and the sensors in the wheels. So I think we can safely assume that the door antennas have nothing to do with the TPMS, the OP's original topic.

Thanks for getting me off the couch.