Stolen cat ... damaged ECU?

Hey all,

The cat from our 2005 Prius Gen 2 was recently stolen, and after our mechanic replaced it with a genuine Toyota exhaust the check engine light stayed on. They tried a second CO2 sensor which didn't fix things.

We just brought it to a Toyota dealer and they said the ECU was damaged when the exhaust was stolen and needs replacement. They are quoting $1,600 for the repair.

Does this diagnosis sound right? I can't find ay other reports of the ECU being damaged by catalytic theft. I'd also love to hear a POV on whether that dealer repair estimate is way off ... the part itself seems inexpensive.

Thanks all!

Niall

PS ECU codes are P0038 P0037

 

Hey folks,

First off, thanks everyone for your initial responses in this thread. I had not resolved this fault since the theft, but have a little more time on my hands these days, and decided to tackle the diagnostics steps in the Toyota manual.

After dutifully following procedure, it seems there's a short between the power to the O2 sensor and the chassis. My Fluke is measuring 140ohms from H13-2 (+B) to the chassis whereas it should be >10Kohm.

Turning to the more educated and experienced members again for advice on how to proceed! I'm guessing the previous O2 sensor was tugged hard during the theft, thus fraying insulation somewhere further up in the harness. My plan, absent better advice, was to open more of the instrument panel to inspect the cable, and try and find intermediate points junction boxes to check the harness. Does this sound like I'm on the right track?

I need to test all of this again tomorrow with fresh eyes but I may be narrowing in on the problem ... though resolving it may get a lot tricker than plugging in a new ECU :-/

Niall

 

Actually, now I am royally confused. If there was a short on the EFI M circuit, presumably there would be a whole lot of trouble, not just this one code. I've attached the procedure I'm working off ... will come back to this tomorrow after sleep!

 

Update: I disconnected the downstream oxygen sensor connector from the EFI M relay via connector IJ1, and confirmed there's continuity and no short in that segment of the harness (i.e., H13 pin 2 to IJ1 pin 4). I'm guessing the 140ohms to ground that I measured when it's all connected up is due to some other circuit downstream of the EFI M relay, and is not actually a fault. That seems to mean there's an error in the Toyota repair manual, so I'm not exactly confident in that either

Anyhoo. I've gone ahead and ordered a new ECM from All Computer Resources. Fingers crossed.

 

I've only tested the EFI fuse, but will reference the wiring diagram and see if I can find others feeding the ECM.

When you say "check the harness for shorts", do you mean testing all pins on all four of the ECM connectors? That seems overkill, but I definitely don't want to blow the replacement ECM, so if that's what I need to do ...

 

Well, I had the battery disconnected when ohming H13-2 (+B) to the chassis (measured @ 170ohms). That pin is fed from the EFI M relay, but there's a bunch of other circuits branching off the same feed via junction connector J1 (ECU, Mass Air Flow Meter, C/OPN Relay, Fuel-Vapor Containment Valve, Canister Pump Module, VSV, Air/Fuel Ratio Sensor) so I was suspecting the 170ohms is through one of those components, versus being a short in the harness. For what it's worth, I disconnected connector IJ (downstream of J1) and confirmed that IJ1-4 to H13-2 has no short, which is where I would expect to find wiring damage if the O2 sensor was forcibly pulled out.

That said, do you think I should go down the rabbit hole and find exactly where that 170ohms continuity is happening ... might be a red herring, but could lead me to a related or different fault?

Niall

 

Update: it was straightforward to disconnect the components downstream of the EFI M relay (by unplugging the ECM, MAF, connector IN1) which let me triple-check there was no short in the harness before installing the new ECM. I also confirmed the engine would start with the new ECM by just flipping the connectors to plug it in (thanks @mr_guy_mann for the tip above).

The official repair manual instructs you to remove the instrument panel to gain access to the ECM, but I first tried a shortcut method posted on YouTube. Unfortunately I dead ended as the instructions weren't totally clear, and ended up taking off the instrument panel anyway, for which I found another video. That was definitely type 2 fun.

Long story short, the new ECM works, and I have no check engine light for the first time since Nov 2020 I took the opportunity to fix the issue with he shifter binding, which had been bugging me for years. Now that I've got my hands dirty and built some confidence, there's a bunch of other preventative maintenance stuff I might tackle

Thanks to everyone in the thread for the pointers and advice!!

PS some photos for anyone else tackling the job: Gen 2 ECM Replacement | PriusChat

 

@Kasra I ordered from All Computer Resources, and it was just plug-and-play.