Tire pressure light on

sorry, no. is there a tpms switch under the steering wheel?

 

I suggest that paying a dealer a "diagnostic fee" might be a very good investment in a case like this.
YOu could spend a LOT of money on wrong guesses.
And it is possible that your test equipment isn't working right either.

 

You've got Techstream and a J2534 cable, so you clearly see the value of preparing yourself well to work on the car. The other piece of good preparation that I'd encourage is to get familiar with the information available to you from Toyota, including the Repair Manual and Electrical Wiring Diagram. Elektroingenieur built a very helpful wiki page about that, here.

Is Techstream in fact showing you that it cannot establish communication with the tire warning ECU? When you do a Health Check, you should get a result page showing every ECU in the car, with coloring to indicate whether Techstream was able to reach it.

For the location of the ECU, see L4 in this screenshot from the Electrical Wiring Diagram:



You may be able to see it by removing the lower glove box, which is easy. It will be an upward reach from there, above the lower tier of slots in the ECU hotel back there.

If Techstream really isn't able to communicate with it, I would suggest turning directly to what the Repair Manual says about that situation and how to troubleshoot it; it's a pretty uncommon situation, so there won't likely be many PriusChat members saying "oh yeah, that happened to me, it was ...".

 

Maybe a dumb question, but have you attempted to do the TPMS calibration procedure? Air up the tires to proper* inflation, press the power button twice without foot on the pedal, press and hold the TPMS button until the dashboard icon flashed 3x slowly, let it sit like that for 3-4 minutes, then power off.

*Based on your definition, the owners manual's, that of hypermilers, etc.

 

Honestly, if the OP has already connected Techstream and as reported it wasn't able to connect, that already confirms something is amiss beyond adjusting the setpoint (which is all that button is for).

 

So.....how is it that you were able to obtain the engineering spec's for that module so that you KNOW that is all the button is for ??
Hint: You don't know that at all.

 

have you tried resetting the pressures?

 

could be a chance that batteries in all the sensors have ran out of charge.

 

how is the 12v health?

did you have to hook tech stream up to the obd to register the fob?

 

i wonder if the tpms ecu connector might have some corrosion.

 

Hmm. If you think that might be the case, you may want to review this TSB and do some very careful proactive investigation of the car, as outlined there, to get as informed an idea as possible what has been replaced already and what future surprises may await.

 

I should note that my 2012 Prius has experienced several episodes of spurious TPMS alerts (a tire gauge shows good pressures) over the past several years. It may alert a half dozen times on a long trip, for ten minutes at a time before extinguishing for a while, then alerting again. This may happen on several different days over a few weeks, then not repeat for nine months, then re-appear again. It has not re-occurred since the initial Pandemic restrictions, possibly due to reduced overall driving providing fewer opportunities.

When it initially suffered several episodes, it happened on both my summer and winter wheel sets (separate wheels and TPMS sensors) in the same month, straddling the seasonal tire swap. Linear Logic was then offering a free firmware update for ScanGauge-IIs, to display individual tire pressures, so I took the offer. No more TPMS alerts happened for the next six months.

When the alert finally did reoccur, I was able to figure out that is was a single sensor not being detected and read for longer than the maximum time limit, then clearing when that sensor would suddenly reappear. When turning the car Off then back On, this sensor would appear as -14.5 psi (i.e. no reading, so stuck at the power-on default value of 0.0 absolute, minus sea level 14.5 to get 'gauge' pressure) while the others would show a reasonable value 35-42 psi. If it was triggered while driving continuously on the highway, the car gave the ScanGauge the last read value. That means the fault wasn't flagged on the ScanGauge, only as the car's TPMS light being lit up, except that the faulty location was showing an unchanging pressure, while the other three locations were showing slightly changed pressures as ambient/road temperatures changed.

I should be tracking this over multiple tire swaps and rotations, to see if the "bad" sensor is always a specific sensor (per seasonal tire set) or a single wheel location. I'm thinking that it has been different sensor codes, but these episodes are sparse and I haven't kept the necessary data.

Sorry to not yet have a solution, but my experience might provide some directions to further investigate.