2009 Gen 2 Prius (NHW20) – Red Triangle After Water Intrusion, Corroded Rear Connector, P0AC0/P0AFA

Thank you in advance for taking the time to read all of this and for any help you can provide.

Hi everyone,
My apologies in advance for the long post, but I really need some help, advice, and feedback, and I wanted to provide as many details as possible about what has happened and what I have done so far.

I have a 2009 Toyota Prius Hybrid Gen 2 (NHW20) and I am trying to troubleshoot a problem that appears to be related to water intrusion in the rear passenger-side area of the vehicle.

Previous issue about a month ago

I should mention that about a month or so ago I had a very similar issue with the red triangle and warning lights.

At that time, I did not scan the vehicle or receive any diagnostic trouble codes. I replaced the 12V battery, and the problem went away, so I thought the 12V battery had been the cause.

However, after the most recent heavy rain, the same warning-light problem returned.

Current issue after heavy rain

This time, I received the red triangle of death, check engine light, and multiple other warning lights.

I used a Bluetooth OBD scanner with the Torque app and received the following codes:
· P0AC0
· P0AFA
Torque identified them as powertrain codes but showed them as unidentified and did not provide much Toyota-specific information.

I also discovered standing water in the compartment that holds the 12V battery on the passenger side of the rear cargo area.

So far, I have:

· Disconnected and removed the 12V battery.
· Removed the drain plug and drained the standing water.
· Dried the 12V battery compartment and surrounding areas.
· Had the 12V battery tested. It tested good and was approximately 90% charged.
· Removed the rear passenger-side interior panel to inspect for additional water.
· Found a large white multi-pin electrical connector in the passenger-side rear quarter area near the hybrid battery cooling fan/duct.
· Found corrosion inside several terminal cavities of this connector. The affected wires are purple, yellow, black, and brown.
· Disconnected both white mating halves of the connector.
· Cleaned the corrosion as well as I could using CRC QD Electronic Cleaner and small interdental brushes.
· Allowed everything to dry and reconnected the connector.

Unfortunately, after reconnecting everything, I still received the same warning lights and had the same problem.

One strange thing I noticed: when I initially turned the car on and received the red triangle and all the warning lights, I pressed the POWER button to turn the car off. Instead of shutting off, the gasoline engine started. I pressed POWER again, and the car then shut off.

Because the problem returned after the recent heavy rain, and because I found water in the 12V battery compartment, I decided to remove the rear passenger-side interior panel and inspect the area more closely. That is how I discovered the corrosion inside the large white electrical connector.

Replacement connector from Pick-a-Part

I then went to Pick-a-Part and found what appears to be the same white multi-pin electrical connector on another Gen 2 Prius.

I cut off both mating connector halves with several inches of wire attached.

The donor connectors were in much better condition than mine. I cleaned both donor connector halves with CRC QD Electronic Cleaner, and they cleaned up very well.

My next step is to cut the corroded connector sections out of my Prius and splice in the donor connector halves.

I am using adhesive-lined/water-resistant heat-shrink butt connectors, with one butt connector for each individual wire.

My plan is to:

1. Replace one wire at a time so I do not mix up the wire positions.
2. Crimp each side of each butt connector.
3. Perform a tug test on every crimp.
4. Use a heat gun to shrink and seal each butt connector.
5. Apply a light amount of dielectric grease to the replacement connector terminals and mating surfaces before reconnecting the two white connector halves.

For safety, while I am doing this repair, I have the 12V battery disconnected and the orange hybrid battery service/maintenance plug removed.

The car has been sitting disconnected while I work on it.

Water leak

I believe the original water leak may be coming from the rear roof/body seams, which I still need to locate and reseal properly.

For now, I bought a waterproof car cover so additional rain does not get inside until I can permanently repair the leak.

Questions about the corroded connector

Has anyone dealt with this specific large white connector corroding because of water intrusion in the passenger-side rear area of a Gen 2 Prius/NHW20?

Does anyone know the official name or connector identification number for this connector in the Toyota electrical wiring diagrams?

Does replacing both sides with clean donor connector pigtails and using properly crimped adhesive-lined heat-shrink butt connectors sound like the correct approach?

Is there anything else I should inspect in this area because of the P0AC0 and P0AFA codes before reconnecting the hybrid battery service plug and 12V battery?

Does anyone know whether this particular connector or any of the purple, yellow, black, or brown wire circuits passing through it could be related to either of these codes?

2009 wiring diagram question

Does anyone know where I can find the complete electrical wiring diagram for a 2009 Toyota Prius Gen 2 (NHW20)?

I found a 2006 Prius wiring diagram, and I know the 2006 and 2009 are both second-generation NHW20 Prius models, but I do not know whether the wiring diagrams, connector locations, cavity numbers, and wire colors are exactly the same.

Can I reliably use the 2006 wiring diagram for my 2009, or are there enough differences that I should locate the 2009-specific diagram?

Separate issue – Multifunction Display (MFD)

Assuming I can get the current red-triangle/water-intrusion issue resolved, my next project is the multifunction display (MFD).

At this point, I cannot see anything on the MFD screen.

The previous owner told me that they had previously sent the MFD out for repair, and that repair lasted approximately 10 years, so it seems like the previous repair held up for quite a long time.

For my 2009 Prius, would you recommend:
· Removing my original MFD and sending it out for professional repair again, or
· Finding a replacement MFD at Pick-a-Part?

I am leaning toward checking Pick-a-Part because they provide a 90-day warranty on the part, so if I install the MFD and it does not work, I should be able to return it for a refund.

If I get one from a salvage yard, what exactly do I need to match?