Hey guys, thanks in advance for any help. It's much appreciated. I'm totally at a loss here, so I really do appreciate any help.

I have a 99 Honda Accord. Engine light came on, code P0135, primary O2 sensor. I replaced it thinking it would solve the problem. Cleared the codes, and within 15 seconds, same code came back on. So I figured it was something else and just didn't have time to deal with it right then, so I just kept driving the car (P0135 code had previously been on for about a month, so I didn't think much of continuing to drive the car.) About 4 days later, my car completely shuts down while at a light. Car cranks but won't start. Did a whole bunch of research and it pointed me to the ECU, so I opened that up. Immediately smelt the burnt electrical smell. Sure enough there was one chip that had melted pretty good. I bought a junk yard ECU off eBay with the same numbers and installed it. Also had a matching ignition, put that in along with the new key. Car started up, but again, immediately threw P0135, and within 30 seconds I started to smell the same exact chip burning. I immediately shut the car off, did some more studying and tested things -

New O2 sensor is giving between 18-22 ohms resistance, which I've read is accurate.
I have good voltage coming to the harness feed.
I've checked continuity from harness end to ECU connectors and they all seem good.
When engine is on, Secondary O2 sensor voltage fluctuates up and down and doesn't throw any codes or burn any chips, so I'm guessing it's working totally fine, and I'm also guessing that's how the Primary O2 sensor should function. BUT....
I have the wiring diagram, and the black and white wire from the Primary O2 harness goes directly to C1 on the ECU. I had to cut that wire. Car still has P0135 code, but at least the ECU chip isn't burning up and the car runs. As SOON as I connect that black and white wire, it starts burning the chip in the ECU. I've also tried completely bypassing the stock black and white wire, going harness to harness with my own new wire. Same thing - as soon as it gets hooked up, it immediately starts burning that chip. Weird thing is that unless I'm reading something wrong, it's being bunt up with only approximately 3.5 volts. So I have no idea why or what's happening.

What is that chip and why is my car burning it up? It's not the ECU, cause this is the second ECU with the same exact chip burning, so what's causing THAT chip to burn? What IS that chip? I recall seeing it labeled on an image somewhere online, but haven't been able to find it again. I'm getting no other electrical issues at all that I've seen. I'll check around for that image again, but anything you guys have as recommendations would truly be welcomed.

My ECU number is 37820-PAA-L61

I've attached a picture of the ECU board and highlighted the chip that is being burnt up.

Again, any help or recommendations are welcomed. Thank you!





Close-up of chip that keeps burning out


C1 wire cut completely, error code on but car at least starts and drives. I CAN'T connect this wire, or else the chip will start burning up.


Entire ECU showing chip location

 

Possible cause may be a short at the primary O2 sensor connector wiring (check the other wiring on that harness too) or with the replacement O2 sensor. With Connector C unplugged from the PCM/ECM, measure the voltage of the Blk/Wht wire with the ignition switch in the ON (II) position (not running).

PCM/ECM terminal C1 is O2 sensor heater control, it is duty controlled when the car is fully warmed up and running. Therefore, there is a pulse width modulated signal coming from the PCM/ECM. The chip that is getting burnt up is probably a pulse width modulator chip.

 

Thanks for the response. Ok, here are the measured voltages at the C connector disconnected from the ECM. Test was done with Primary O2 sensor connected to harness, ignition set to (II) ON position, not running.

Pin Number and voltages -
1 - 11.74
2 - 7.32
3 - 0
4 - vacant
5 - 0
6 - 4.43
7 - 0
8 - 0
9 - 0
10 - 0
11 - vacant
12 - vacant
13 - vacant
14 - vacant
15 - vacant
16 - 0
17 - 0
18 - 4.49
19 - 0
20 - 0
21 - 0
22 - vacant
23 - vacant
24 - vacant
25 - 4.48
26 - 4.48
27 - 4.48
28 - 4.48
29 - 0
30 -0
31 - vacant

NEXT TEST - Checking voltages on engine bay harness (NOT Primary O2 Sensor, but the side that plugs into it)
Ignition set to (II) ON position, not running.
Black/Yellow - 11.75
Black/White - 0
Green/Black - 0
White - 0.4

NEXT TEST - Checking voltages after applying power directly (with a jumper) from engine bay harness Black/Yellow to Primary O2 sensor power input...
Here are the voltages on the OUTPUT of the Primary O2 Sensor - (using the adjacent wiring colors since they don't correlate)
Black/Yellow - 11.75
Black/White - 11.75
Green/Black - 0
White - 0

 

I don't notice anything unusual from your results.

 

Hmm... Ok, thank you.... Any ideas for additional troubleshooting, then? It's the same exact chip that's burning up in two different ECMs. So it can't be the ECM causing the issue. Any additional ideas? Anyone?

Do you (or anyone) know where I can find a diagram of my ECU that will show me exactly what that chip is?