Mystery P3102 Shift Actuator, Gen 2

Over the years, I have used this great site to learn and repair all the quirks associated with owning & driving a Prius, and would like to give back to this community. I recently had a mysterious problem, which stumped (supposedly) the best-of-the-best, and cost me over $1,000 in unnecessary troubleshooting and misdiagnosis work. I would like to share, in case it may help others.

I own a very nice and well maintained 2006 Prius with ~200k miles of mostly long-distance driving.

Last month, after highway driving for ~30-40 minutes: The cruise control disengaged; The car beeped; Numerous warning icons appeared on the dash and MFD (exclamation inside triangle, exclamation inside car icon, VSC, exclamation inside brake icon). There were no operational issues (no limp mode, no loss of power, no loss of braking, no loss of control, etc).

I pulled off the road, placed the transmission in N, and pushed the e-brake switch. The MFD then displayed "Caution - There is a problem with the transmission P lock mechanism. Park your car on a flat surface and fully apply the parking brake." I attempted to put the transmission back into D, it would not engage, and the e-brake switch rapidly flashed blue.

I turned the power/ignition OFF, and after a few minutes turned power/ignition back ON. There were no warning messages or icons displayed, the system had re-set itself! I was able to put the car back into D and continue down the road.

After 30-40 minutes of highway driving, the process repeated itself, only this time I did not pull off the road and stop, I kept driving until I got home (warning lights / messages / icons stayed displayed, but there were no issues driving the car). Again, after turning OFF, the warnings reset and were not displayed the next morning.

I took the car into my local dealer (Reno Toyota), where they pulled the following DTC codes: P3102; U0100; U0111; C1554; C2300; C2318. They kept the car for 4 days, trying to understand the problem, and finally recommended that I replace the 12V aux battery (w/o first checking to see if the battery was actually 'bad' … I had replaced this battery ~1 year ago, but the technician had 'assumed' that it was original). I authorized the repair, and paid $500+. On the way home, after ~30-40 minutes of highway driving, the same identical problems re-occurred.

I contacted Reno Toyota with the unfortunate news, and they said I probably needed a new hybrid battery (without inspection or testing). I responded that I still get combined ~51 MPG, and asked how their analysis made sense (they didn't need to make sense … just make money for the dealership?).

I finally found a great hybrid specialist (Sierra Hybrid, Carson City), who has fantastic information-sharing capabilities (global networking), and after a few days of seeking 'good' information from his peers and eliminating other possibile issues, Gene diagnosed an intermittent problem with my Shift Actuator. He replaced it with a good used unit, and all problems disappeared. The car now drives normally again!

It seems that DTC P3102 (Transmission Control ECU Malfunction) was the most accurate code? Why would Toyota's software engineers program all those other spurious DTCs … to confuse their own "highly trained" technicians?

The takeaway … if you experience similar warning lights, messages, and DTC P3102, suggest to your "highly trained" Toyota tech to first check the Shift Actuator module, before blindly replacing other expensive parts!

 

JC - I am fairly certain the Toyota part number is 35580-47010 for my 2006, but would recommend an internet search if you are planning on obtaining the part.

Chapman - These are the basic DTC explanations:
* P3102 - Transmission Control ECU Malfunction (INF code also needed)
* U0100 - Lost Communication With ECM/PCM A ; Control ECU Communication Error
* U0111 - Lost Communication With Battery Energy Control Module A
* C1554 - Power Supply Relay Failure (power source relay circuit malfunction; power steering ECU)
* C2300 - ATC Actuator System Malfunction
* C2318 - Low Voltage Error (power supply malfunction)

Funny ... all these DTCs for one intermittent Shift Actuator Module failure?

Generally, it is recommended that all ECU wiring connections and harnesses should be checked for fit and continuity when two or more "U" DTC codes out simultaneously, which could take hours and tear the car half apart just to access all these areas.

To add to the confusion, also reference the following Toyota Service Bulletins:
* TSB-0174-12 - Overly sensitive monitoring logic with ABS/VSC system issues
* TSB-0047-09 - IG1 Relay failure
* ZG1 - Brake Actuator Assy triggering various brake system lamps to illuminate

Further, Toyota has a flowchart for its mechanics to start replacing various batteries and ECUs until the problem is solved! VERY expensive!

As you can see ... all over the board, which is why I offered this thread! Toyota's software engineers really need to simplify the self-diagnostic failure codes for all ECUs / modules!

 

JC - Yes, I think it is ~$600+ new, but a "good" used module can be found under $100.

Bisco - My "new-found" mechanic / repair shop in Carson City NV is ACDC-trained (Auto Career Development Center). My understanding is that, besides intensive hybrid training, ACDC offers their tribe (graduates) networking / sharing abilities, so a stumped mechanic can reach out to others to solve unusual issues. Go to ACDC's website to locate their trained mechanics, there might be one in your backyard. Hope this helps.

Wrapping this up, I will state the obvious (but something I just realized): When I was dealing with a Toyota dealer, trying to explain these unusual symptoms and issues, I was forced to deal with a group good-intentioned but basically stupid persons - Service Advisers & Service Managers (their jobs are mostly to SELL SELL SELL). Similar to talking through a translator with ulterior motives? With my new mechanic, a small 2-person shop, I am dealing directly with highly trained / highly motivated / intelligent / experienced technicians. The difference is obvious!

 

Bisco - If you go onto ACAD's website, you'll see they have a "certified / trained" mechanic / shop near your location. I am certainly NOT recommending any repair shop from NV (2,000 miles away), just saying it appears you might have several choices close by? Check it out!

Ray - HA!! I didn't see that coming. I saw the group at Donington in '91, what a crowd, what a party, what a concert ... WOW.

Eric - Diagnostics labor, $210 ; Replace part labor, $190 ; Part (used), $95 . I was very happy to pay for a successful repair!

 

Bisco - sorry, I meant ACDC website. iPhone is hard to hit proper keys!