TPMS Management with Techstream

About 5 years ago I was studying the various messages that the TPMS ECU sent and received. One of the things I discovered was that the Prius ECU supports 5 sensors, just like a few other Toyota vehicles. I bought a sensor, had it installed, and set the ECU for 5 sensors. It all worked, and I've been able to read the spare tire pressure with Techstream instead of digging the tire out of the trunk. Everybody else was complaining about even having TPMS, so it didn't seem worth mentioning that you could add another sensor.

The program I used was a one-off test, and doesn't even exist anymore. But if someone wants to write a program to enable TPMS on the spare, here's the GEN2 protocol from my records:

82 2A F0 21 06 ......... Query # sensors registered
84 F0 2A 61 06 x0 y0 ... Reply: x=main set, y=2nd set
........................ x:8= 4 sensors, x:A= 5 sensors (high 3 bits of Each byte)

84 2a f0 3b 06 x0 y0 ....Set # sensors that can be registered.
.........................x=main set, y=2nd set
.........................x:8= 4 sensors, x:A= 5 sensors (high 3 bits of Each byte)
82 f0 2a 7b 06 ..........Reply

Specifically, the 3rd message is the one that sets the number of active sensors. "84" specifies 4 data bytes, "2a" is the address of the TPMS ECU, "f0" is the address of the interface, "3b" is the set command, "06" is the function number, and "x0 y0" are the new values. The high order 3 bits of x and y represent the number of active sensors, with the 3 bit values of 4 and 5 being the only ones tested. Perhaps values 0, 1, 2 & 3 would also work.

You must use a Drewtech or MiniVCI interface - the ELM doesn't support the protocol used (forget about using Torque). The Drewtech website documents the API.

Note also that the "y" field determines the number of sensors in the second set. There is probably a pin on the ECU which, if grounded, selects a second set of TPMS sensors. Comparison of TPMS ECUS between the Prius and some other Toyota vehicle that supports the second set might reveal where the signal is controlled. Several Lexus vehicles have a selector switch in the glove compartment.

 

5 sensors probably because full size spares might be used?

 

Thanks for putting forth all this information! It was helpful.

 

I'm in the same boat with a sensor that is going out then has a good streak for a while but wanted to ask are you just doing this as an experiment instead of having the one bad sensor replaced? I have a new sensor and am looking at new tires so was going to use TechStream with your tutorial to narrow down which TPMS sensor is bad once it's light comes back on then swap it when I get new tires since they'll have access to the TPMS. Writing down the TPMS ID before of course.

 

So did you install a new denso one in the spare and the old spare one into the messed up tpms sensor? A bit confused where the sensor that you put the fake out method goes.

 

Any reason why you didn't change the trmp on the front right tire like you did in #3? Guessing you're just waiting for the tire to need to be replaced first?

 

Each time I get the TPMS error and hook the car up to my computer to open Tech Stream it clears every time on it's own. This does not help in determining which is bad. Any suggestions on keeping the error up so Tech Stream can read it?

 

TPMS error seems to only happen on a 40F and above day when I'm eating my lunch in my car so it's running for at least 30 minutes. Shows on the dash while I have my OBD2 USB connected hooked up but as soon as Tech Stream starts it clears. I'll have to lower the pressure in one and see what tech stream does with a "real" tire issue.

 

I had TIS 10.10.018 on my 2006 (built 11/05) last night, have had the light for months. After running a full Health Check, including entering the info for TPMS (current temp, expected low temp, expected pressures fr/rr, IIRC), it showed 3 reading pressure, one NULL.

Today, if I have the energy (dealing with DTCs on BOTH the 06 and 04), I plan on setting the tire pressures to 50, 40, 30, and 20 to track down which one is dead. I have 4 sensors from a boneyard 08 that I will test one by one by tossing their IDs into TIS to see if they read with a binder clip or finger pressure. They were only $10, so if just one works, I should be golden. Then I'll see if I can use bar clamps to compress the tire bead enough to swap it out, get the bead popped back, and the tire filled, so I don't have to pay a shop to do it.

My MIL's 06 also has the light, so this is a test run to see if I can track down which of hers are shot and if I can replace them in their garage in a quick visit.

 

Does Florida require operational TPMS, would failure put your car off the road?

 

One way to identify which TPMS is which is to park the car one side to the sun. After that side has baked a few hours, use Techstream to read the temperatures in the tires. The two on the sun side will be higher. Then turn the car 90 degrees with the sun at the front or back. Bake another few hours and you'll see which are front and back.