Now.. P1636 - HV ECU Malfunction

Last month a driver hit the rear driver's side corner of my 2002 Gen 1 (148,000 miles) . The car was only lightly hit, just pushing in he bumper wrap on the rear drivers side corner.

During the one mile drive home the Prius threw a code.

• My hand held Toyota tester confirmed a module voltage was low.
• The module was replaced
  
• I emoved the bumper wrap and heated it to pop out the dent, restoring the shape of the bumper wrap.

II left the area for a couple of days. During that time it rained cats and dogs. When I went to drive the car I discovered I'd mistakenly left the front passenger door's window down 3". The whole passenger side of the car was wet on the inside. The rear foot-well had about 1 1/2" of water pooling in it.

I cleaned up the water and attempted to dry out the car over the next three warm days.

Everything worked for about three weeks.

Two days ago the Prius threw a P1636 code... and then the scanner could not detect the car, then this repeated itself. I searched the forum and the problem points to the Engine ECU on the passenger side firewall, under the glove compartment.

So, my question is:

Has the Engine ECU been destroyed by the moisture? I've got the carpet pulled down and I'm about to pull the Engine ECU and start to dry it out while examining the connector pins to try to recover the ECU.

Before I start, does anyone have any thoughts? I only want to do this once. I'm not excited to buy a used ECU and go through possible reprogramming.

Thanks in advance.

 

Thanks for the help, Brian. I think it may be OK, as I can clear the codes and have the car run... for a while. So, I'll dry it out, makes sure the carpets and connectors are dried out and see what happens!

 

I'm an hour west of Chehalis on Hw6 and Hw101. I can remember may times that I-5 would flood and close down for a couple of days. Yep, if you live here you'd best like rain.

I'm reconsidering the problem with the Engine ECU because of two thoughts that popped into my mind last night;

• 1) When I connect a Bluetooth scanner to the OBD port a brake light is set, and often the scanner won't report to my android or Apple devices, and;
• Every once in a while, and it's becoming more often, that when I tried to start the Prius the engine lamp would be set and the engine would not start. By simply restarting the Prius, the problem went away. I never considered that a problem, until now.

So, I'm beginning to think that the Engine ECU was starting to fail long ago and the moisture may have been the last straw.

I'll still dry out the ECU and interior and see how it goes while I'm waiting for a used ECU.

 

Well, today I went out and took out the Engine ECU and was surprised to see how much moisture there was around the ECU. I removed the cover to the ECU and applied a heat gun to the metal case to cook off any moisture inside and then reinstalled the cover.

When I went to put the ECU back into the car I noticed a moisture dripping down from the up above on the firewall. I wiped that down and dried the area off as best as I could.

I half expected the vehicle to not start after seeing all the moisture. But, it started like a charm. Now I'll see tomorrow if it will run a few miles without a hitch.

The part number on the ECU is: 89981-47061

Here's hoping I don't have to buy a new/used one.

 

In early October I had repaired the traction battery. I then left for a couple of days with the Prius sitting outside my garage. While I was gone there was a huge wind and rainstorm. I came home and a couple of days later decided to take the Prius out for a drive. I opened the drivers door and sat in the drivers seat and looked to my right to see the passenger side front window was down four inches. That made my heart skip a beat!

The whole passenger side interior of the car was soaked to the bone There was 2" of water in the rear passenger side footwell. The front carpet was soaked, but no pooling water, that had all flowed under the front seat to the rear footwell.

Today I was quite surprised to see water still up in the dash area. I'll be keeping an eye on it and trying to dry it out.

 

Confident is such a big word. But yes, I do think that this area is the a place where the last bit of moisture is hanging on. During the days it was "drying out" in the sun the inside of the windows (with all the windows down a couple of inches) were very fogged up.

I suspect that there's still some water up in that dash in nooks and crannies under the glove compartment. If I continue to have problems I'll drop the glove-box and see if I can spot more moisture.

I have a heat gun and I'm not afraid to use it.

 

Yep, we had a good storm a couple of days ago. There were 80mph winds and 25ft seas. It damaged my neighbors roof (His house buffers the wind around my home. I pray his house never burns down.). The rain was constant for a couple of days, and yes, it was almost sideways. But, hey, I don't have to shovel it like I did in Wisconsin! Yay for rain!

Well, I took the Prius out for a drive today. 2.5 miles into the drive the problem occurred again. The area was dry this morning, and still is. Now I'm sadly convinced that the problem is the ECU. Parts Market is going to make another $50 out of me this month.

 

Early this morning I was thinking back to my career as an IT guy. In the early 2000's I was replacing motherboards of computers for problems with bad capacitors. I thought: "I wonder if that could be happening with my ECU?"... and did a Google search on "Gen 1 Prius ECU capacitors." I was rewarded with lots of sites with horror stories about ECU's and bad capacitors. I'm now wending my way through these sites. I'll likely pull the ECU and remove the PCB to see if there's any physical damage I can see with the board.

I found this an interesting read:

Lexus and Bad Caps

If Lexus was having problems with bad caps, then I suspect the Prius would for the same years production. Toyota likely would likely source the ECU from the same company. If that's true then the same problem carries over to the Gen 1 Prius.

My next steps will be:

• Inspect the ECU for physically damaged capacitors
  
• If any of the ECU capacitors are bad/marginal it would be more cost effective to replace the PCB
• Then, repair the original with new capacitors,
  
  • test and
  • put it on the shelf for a backup.

Now, this problem had just officially become very, very interesting.

 

I took out the ECU and look at the caps. There's no "obvious" damage such as leaking or domed caps. However I did look at some of the caps that are raised up off the circuit board. Some have the rubber bottoms coming down below the lip of the body of the cap, as if the cap is ejecting them. But, I'm truthfully not sure they're bad. Here's a picture looking at one end of the PCB:

 

Thanks Brian, that is the conclusion I came to.. no obvious damage. The wrecking yard sent me the wrong ECU saying it was a direct swap. We both know better, esp since the one plug would not fit. Oh well, now to buy another one from a yard that won't sub parts.