Fixed! Rear Hatch Leak and related problems. A journey!

Telling this story as a way to say 'thanks' to the PC community as this has been a great resource to help with troubleshooting the above issue. Hopefully may help someone in future with a similar Gen 2 problem?

2008 Prius (reg Jan 2009). 125K miles. I've owned it for 110K/10 years.

Never had any major issues other than a wheel bearing replacement and the rest have been age related corrosion underneath (brake pipes mainly), sticking brake pads (every couple of years) and then just consumables like tyres.

Driving along motorway (UK) about 70mph on a dry evening and the VSC and Brake System warning lights pop up in amber. Red triangle of doom comes up too. Plus the 'Car with Exclamation' in the LED display. Car seems to drive as normal. I carefully drive the remaining 12 miles home without incident.

Car would not go into 'EV Only' mode and Park Assist light flashed on the button when selected. Car revved unevenly and hesitated when pressing accelerator when parked. HV battery seemed to charge all way into green from engine, which it does not normally do. Otherwise the Hybrid system seemed to function pretty much as usual.

Next day - I didn't have an ODB scanner and *suspected* that it could be the infamous Inverter Water Cooler Pump failed (P0A93). Checked the cooler reservoir and there was not to no movement. Checked the pump and it was running (sound/vibration). Checked for any air in the system causing the circulation to be poor - bled it (no air) - squeezed all pipes while pump running and flow did (very very marginally) improve but I still suspect the pump may be running slow due to old age (I believe it was replaced under recall about 9 years ago).

I decided to get a code reader (Veepak OBDCheck BLE+) and tried various iPhone apps. Settled on Dr Prius, Car Scanner + ODB Fusion. I found Car Scanner was just about good enough for my needs this time - but probably need something a bit more comprehensive in future. Still more testing and learning to do on apps for future reference/use.

Scan did NOT show P0A93, so I counted out the cooler pump as the source of the problem. By this time I'd already ordered a new Toyota pump and coolant (at good prices). So I will replace the pump anyway in Spring.

Scan showed a 'Historical' POA 85 (Hybrid Batt Pack Cooling Fan 1) code. I figured the fan might be needing a clean or may have a fault. So I stripped out all of the trim from the rear of the car (except for the left side/near side UK). Blower fan was very clean already. Removed and tested fan and relay - both good. refitted fan and ducting and gave up on that as the cause.

Scan showed two other (Confirmed/Present problem) codes:

1. P3000 - HV battery malfunction. No sub codes available to assist. Basic (free) Dr Prius showed battery cells within around 0.1V of each other, running nice and cool and charging/discharging fine. So I counted out major HV battery failure. But could not diagnose any further without better tools.

2. C1641 - Raw Code 5641 - Self Parking System. There was not to nothing to find on the internet/PC about this error. So again I was stumped as these failures seemed unrelated.

I found a tiny amount of water in the 12V battery well, a little in the spare tyre well and a small puddle under the HV battery pack. I found the source of the leak was dripping from the plastic trim above the 12V battery. I started to consider the possibility of corrosion to a wiring harness connector throwing up the random faults - maybe on the HV battery control gear. Could not see where water might have contacted any electricals. However, I still did not remove the left hand rear quarter trim as I thought the leak was only on the right side. Mostly I just didn't want to tear out more clips and bolts unless I really needed to. Big mistake!

Car had been out of service for a few days at this point, so I booked it into the local Toyota dealership for a £95 1 hours diagnosis. They basically removed the left boot/trunk trim, saw a small puddle of water in the left rear quarter well (opposite to the 12V battery) and found a stained water track running down the inner arch of the rear left wheel. The stain was green corrosion dripping down from a wiring connector! That connector was related to (at least) the Self Park/Park Assist system. As with the right side leak, water had been running down the inside of the angled frame from the area around the top of the hatch door/hinges. So basically both sides had been leaking - just a little at this stage. Not enough to slosh around the boot/trunk and alert me. It had been dripping gently down through the sound proofing matt behind the surface trim and finding its way into the base of the car.

They quoted 2 more hours (£195!) to fixed the corroded connector and find (but maybe not fix) the source of the leak. So I dried out the connector myself, scraped off the dried crud, scraped the connector pins clean and checked the resistance across the pins. Reconnected it and started the car. The VBS and Brake lights went out. I wiped the codes using the app and the Triangle and Display errors vanished. Test drove the car - all problems had cleared up.

So I only had to find the source of the leaks and it turns out that it's a very well known problem of ageing Gen 2's. They crack along the panel joints running from the rear roof gutters, where they meet with the plates for the hatch surround. Once I removed the removed the (snap on) roof gutter trims and cleaned out the crud, it was evident that cracking had started but it was very minor compared with some examples found on YouTube etc.

I bought some clear silicone sealant, cleaned the area with meths and ran a small bead of silicone along the length of the crack. I'm now waiting for it to fully cure before testing for leaks tomorrow. I hear that the hatch door dampers' mounts can leak in a similar way through the bold holes - so maybe this is not the final fix yet? I will update on the results.

Just thought it might be useful for readers with 'error light' problems to see the full journey I went through and perhaps skip the time and extra costs! For example - knowing what I do now, I would have still first checked the inverter coolant pump - which takes about 60 seconds. But then also check for cracks in the rear roof as water ingress here has been the cause of so many similar 'random' error codes for others. Plus - always consider that water in other parts of the car may be the source of strange problems suddenly appearing.

I will post pictures in a couple of hours.

 

Pictures to accompany my OP. First time posting pics - hopefully works as intended!

Circle around a drop on edge of plastic trim, above 12V battery.

Where the drip lands (cooler duct) when trim is removed.

Water gathered under HV battery pack after it rained with rear trim removed.

Signs of water in spare wheel well.

Rear left (from rear view) wheel arch inner skin - see green stain below where connector is mounted.

Conn. corrosion. Wiring from Park Assist system (plus other system?)

Conn. corrosion.

Conn. corrosion.

Fine crack with arrows showing each end of the crack. Worn paint shows worst areas.

Fine crack with arrows showing each end of the crack.

 

Thankyou glad it was useful. I’m not sure off top of my head whether your error code is related to same area of problem (rear water leak). BUT if you do find cracks in that area then you’d really need to fix them regardless imho in order to avoid future issues anyway. The cracks were not very obvious in my case and took a good clean and a close look to confirm they existed.

To answer your question: Yes the problem has gone and not returned. The next few days I doused the back of the car with water and did not find any signs of water ingress. I also took the precaution of wrapping the problem electrical connector in plastic to avoid possible future leaks.

I shoukd (but have not yet) check, after these few weeks since the repair, whether there are signs of water leaks for conclusive proof of a fix. I will do soon and post results.

So it seems the tailgate cracks and leakage is ‘a common thing’ and one solution is cleaning + silicone sealant to fix it.

Happy to answer any other related questions if you have any.

cheers, Tony.

 

Hi Tom and many thanks for your thanks.

Sorry to hear of your troubles. Car electrical faults can be difficult and frustrating and perhaps mores on Hybrids due to their added complexities. I first didn't want a hybrid because (as a mech engineer myself) I thought increased complexity meant decreased reliability. I must say tho that the Toyotas are amazingly reliable.

I think the first port of call for you would be to fix the leak that's letting water into the compartments either side of the spare tyre (UK!) well. And to fix that, the first and easiest port of call (on an aging Gen 2) would be to at least check (and probably seal as. matter of course) those roof areas I mention in my post. The cracks can be difficult to see, even after cleaning up the area, so adding some silicone is possibly a good idea anyway. Dry out the back of the car and wait for the next rain storm (or take a garden hose to the area) and see what happens in terms of new drips.

It helps to remove the two side trim panels at the rear compartment (boot/trunk) too to spot whether any electrical connectors have been exposed to water - they will likely show traces green corrosion on the connectors if so and they may well be contributing to your problem. Clean up any you find - but there are only one or two connectors in there anyway. Water also can find its way into the area of the High Voltage (HV) battery case (mine had a large puddle underneath and this depends on the tilt/angle the car is parked when the leaking happens) and cause corrosion to the major connectors in that area, but that's more likely to throw up major HV battery/hybrid system fault codes. Having said that, it's possible to misdiagnose low voltage (12V 'starter battery') faults as a result of problems elsewhere in the hybrid electrical system. So it's probably worth taking off the trim from around the HV battery pack and taking a look for signs of water ingress. You'd have to take the lid off the battery case to see the connectors inside and that's a bit of a larger job, which I didn't do.

It's also worth checking that water ingress has not been dripping onto the connectors of your 12V battery as there is quite a complex set of connectors there and could easily create all sorts of errors/problems if they short. The water from a roof leak can/does drip down directly into that area.

Other than that, you might try getting a Toyota dealership to do a fault diagnosis as it may be worth the (not cheap!) cost/trip to help save you having to buy a new car. But definitely fix any leaking problems and dry out the interior of the car as a first step (to see if the problem fixes itself) before doing that.

Of course there are a number of other ways the 12V battery can have problems and leaving the car for an extended period with (for example) an interior light on or (as you say) the car left unlocked or not properly locked are known issues that will flatten the 12V battery and you need to trickle recharge them gently once they are flat, if you want to preserve their life.

Indeed, best not (re)charge a battery with an external charger with the battery electrically connected to the car system . . .

I've just had to replace the whole exhaust system (inc cat) on mine as it had rusted out in at least three places and the system broke into four pieces . . . But it did last 14 years in the UK weather and winter road salting . . .

Best of luck, Tony.