NOT Normal P Lock Malfunction - ONLY Happens Over 80 Degrees. Never When Cooler

The P lock error from that freeze frame happened 1 second after I'd backed out of the driveway, put it into Drive, and started driving. That was after the car had gotten the error earlier, and I let it cool down for 90 minutes or so and cleared the code, so I suppose whatever causes the error was still fairly hot from the earlier drive.

Do you have any insight into where I could look for that periodically lousy connection? Is it likely to be in the cable to the shift actuator?

Do you think it's likely to show different readings if it were to go into error mode while driving on the highway, as it often does?

 

When the P lock error is on, something apparently remains engaged and powered, because it will sometimes drain the battery down to 12.2V in 90 minutes. When the voltage is that low, it won't eve n go into gear. And when I shut off the power, it seems like it stays on because the loud beep stays on even after shutting off the power.

I've attached two images of what it looks like when the P lock error is engaged and the battery has drained to 12.2v~. The hybrid battery shows completely empty, even though it isn't. And the gear indicator just shows empty squares and no letters.

If the voltage is around 12.3V then it shows the drive letters, but it won't shift into them. It seems to need 12.5V to shift into gear.

Maybe these are clues, I don't know.

 

I bought it in Northern California in 2013 and was there until 2017. I road-tripped throughout the West and was in 100+ heat several times during that time and never had the issue.

In 2017 I went to Southern Indiana. It's way more humid in Indiana throughout most of the year compared to California. The heat is no worse here though. Rodents eating wires and things happened while in Indiana, so it could be that. But I can't find any damaged wires that I haven't already repaired. They ate off the wire to the oxygen sensor and one wire to the M9 plug on the front of the transmission, and six wires to the right headlight assembly. I repaired those. The P lock errors started 2 years before the squirrels at those wires so I don't think that's the issue. I have blown the hair dryer on those wires and plugs for minutes and the error never happened.

I can't see or feel any damage to the wires coming out the back of the inverter, but you can't see them very well. I blew the hair dryer on them for a few minutes and didn't get the error. You'd think that if it was a wire in the engine compartment, it would get plenty hot while driving and error even in cooler weather. Maybe not though.

You're saying to check continuity when I have the P lock error. But wouldn't pulling out the HV safety plug to check it delete the error?

You said "under" the inverter, so are those different cables that the ones I see coming out the back? I guess they'd be the orange ones?

 

RE: the transmission ECU

I have put the car heat on full blast and blew the 140 degree hair dryer on it for a few minutes and didn't get the error.

And for the reverse temperature test, I ran the AC on high for 10 minutes in the driveway. Then kept it on full blast while driving. I got the P lock error.

So I don't think it's the ECU getting too hot that's causing the issue. I also did the volt and resistance tests on the wires as outlined in the Toyota repair guide, and they checked out fine.

Maybe the ECU could still be the problem. I don't know enough about what it does and how it does it to speculate.

 

RE: something in the shift actuator circuit. Many people say that the shift actuator rarely goes bad, but that doesn't mean that mine hasn't.

But the heat causing it is what has me stumped. If 85 degrees for instance makes the error happen, surely in normal driving conditions even in the winter, the transmission would get hotter than that and should make the p lock error happen. But it doesn't. So that makes me think it's not the actuator itself.

Same thing with the wires coming out of it--surely they'd get hotter than that from the engine and transmission running regardless of what the air temperature is (but maybe not?) As for the parts of those wires that come into the car, temperature doesn't seem to cause the error either, as I outlined in message #48 above.

So this leads me to think it's some wires further from the engine compartment and not inside the car, since the error still happens with the AC on full blast. It's possible that there's too much heat somewhere near the hybrid or 12v battery that the AC doesn't get to, but I've ran the hair dryer on all of the wires that I can see back there and never get the error.

So that leaves the wires in the back under the car. I ran the hair dryer on all of them that I can see, three separate times, but it never happens. Maybe there are some wires back there that I can't see, like above the fuel tank. I speculated that there may be some in the frame hidden from both underneath and inside the car. Maybe I need to take off the interior trim and put the air dryer on any wire that I can find. I don't know if there are any related wires around there so it might be a wild goose chase.

There's the orange wire that runs below the left side under the car. It's covered by a white plastic guard. I took off the very back piece and put the hair dryer to it and didn't get the error. I blew hot air on the full length of it, but didn't take the white plastic guard off. Maybe because of that it didn't get hot enough. Someone commented earlier that that wire is not likely to be the issue because heat would be disappointed along its length. Not sure if that's the case or not. Maybe I should take off the plastic guard and try it again.

If not these things, then maybe the hybrid battery is the issue. I've heard that corrosion on the internal wires and plates could cause these issues. I'll have a new OBD sensor tomorrow so I can run the Dr Prius battery health tests. Not sure if they'll pick that up though. Maybe removing the battery and taking it apart is the only way to know.

 

Yes, I read that thread and I did check pin 13. It had 13.88V. I said that I tested it in post #1, but I didn't say if I tested it when the P lock error had engaged or not. At this point, I can't remember. It's worth checking again though and I'll make sure the error is engaged while checking.

I also had the jumper wire from the left side of the Pcon fuse to the blue wire in that connector at the top of the fuse block for three years and it didn't stop the issue from happening. I don't know if that's the same blue wire that runs to pin 13 at the TCU. If it is, it very well could be that the wire is bad between the fuse block and the TCU so the jumper in the fuse block didn't help.

I wonder if I should just run a jumper between a good 12V wire like the guy did in post #11 there? He said that means the p con circuit doesn't have a fuse protecting it anymore which doesn't sound good. If that fixed the issue, I assume I could add a 7.5V fuse to that jumper wire. Not sure if it would be in the proper place to prevent whatever damage the original P con fuse does.

 

I THINK I MAY HAVE FIGURED SOMETHING OUT!

First, I checked pin 13 without the P lock error and the voltage was fine--13.88V with the power on. Then I went for a drive. 88 Degrees outside. Less than two minutes later the P lock error happened, so I went back home and checked pin 13 again. Still at 13.88V so that's not the issue.

The P lock error wouldn't delete, probably because it was still too hot. So I left my multimeter attached, drove, and watched the voltage. It only varied by a few hundredth of a volt--13.78-13.84 depending on how much I was accelerating and/or the hybrid battery was working.

Then I decided to do the error code P3102 diagnostic procedure (attached) again. I did it when it was about 78 degrees several days ago and got nothing. So I decided to do it again today when I had the P lock error and it was 88 degrees.

I think I found the issue. Section F, "standard (Check for short)". It's supposed to be 10,000 ohms or higher. The PCON and PPOS wires on the T4 connector tested 0 ohms. The PCON and PPOS wires on the H17 connector both were 350 ohms. All WAY out of range so it appears that there are shorts on both wires that only happen when something gets in the mid-80s or higher.

The suggested fix is "REPAIR OR REPLACE HARNESS OR CONNECTOR" The connectors are probably fine since I tested the wires inside the connectors. So that leaves replacing the harness. That seems like a major PITA since it seems that the wires go to multiple connectors.

Could I just cut all four wires an inch or two outside the connectors and run the same gauge wire between them or is it more complicated than that? I don't know if it's just the wire between the connectors or if there are other components in between or wires coming off of them and going other places or not. If that's the case then I assume the simple jumper connection fix wouldn't work.

 

Do you think I tested wrong?

I followed the repair manual:

(f) Check the resistance between the wire harness side connectors.

Standard (Check for open):
Tester Connection Specified Condition
PCON (H17–9) – PCON (T4–7) Below 1 Ohm
PPOS (H17–10) – PPOS (T4–8) Below 1 Ohm

Standard (Check for short):
Tester Connection Specified Condition
PCON (H17–9) or PCON (T4–7) – Body ground 10 kOhm or higher
PPOS (H17–10) or PPOS (T4–8) – Body ground 10 kOhm or higher

I used one of the silver bolts to the right of the H17 connector for a ground. It was attached to other metal. Maybe into the body.

But maybe I need to use one of the "official" grounds as shown in the manual? "IK" is near there. Don't know if it's marked or I just need to look for some bare metal in that area.

I don't see damaged wires anywhere. Given that heat causes the error and that having the AC cranked up doesn't keep it from happening; I think it must be outside of the cabin or perhaps where it goes through the firewall. But again, I can't see or feel any wire damage from above or below the car.

I'd unwrap the tape from the wire bundle coming out of the firewall and check, but I don't think you can even get a hand on it without removing a bunch of components.

I have the wiring manual and I'm doing my best to decipher it. On page 262 I see H17-9 going directly to T4-7. There's nothing shown in between it so I think that means it's just a straight connection and so my jump wire might work.

But on page 86 it shows H17-10 going to "junction connector J14" and other places and ending at P6-5. Then on page 106 it shows H17-10 going through "junction connector J14" and ending at T4-10. Same on page 228. So that's a more complicated wire.

I'll look for that Junction connector and around the firewall tomorrow. Thanks for the help!

 

Gotcha. I didn't mean for that to come across like I was threatened by it. I was just asking to learn if I should do it differently.

The J14 is in several places in the diagrams and seems like several wires run into it so I don't know if my jumper idea would work and just bypass the J14 by connecting the two connectors. Clearly, that wire is going through J14 for a reason and probably other wires in those circuits need the signals that go between PPOS (H17–10) or PPOS (T4–8), so me breaking that connection might cause more trouble.

I'm fairly mechanical and can fix a lot of stuff, but that's probably beyond what I should be messing with. I'll try to find J14 but I'm not sure what I'm looking for. Maybe I'll be able to cut the tape off the wire bundles and follow the wire from the H17.