Hi, I changed a clutch and while reconnecting the oxygen sensors above the transmission I accidentally plugged in the harness to the harness (one O2 sensor harness plug is male, and one female, same plug type), and plugged a senrsor to the other sensor. I had originally received two codes, P0135 and P0141, which makes sense given the ECU could not read either sensor. After figuring out my error and plugging everything in correctly, the P0135 code went away and the P0141 remains. I checked fuses 6, 10, and 15 under the dash, which I thought may have been the issue, and just today replaced the secondary O2 sensor (given P0141 is the "O2 Heater Sensor Malfunction (Bank 1 Sensor 2)").

I've seen one thread that suggested that the ECU may need to be replaced, however given my ECU situation I would rather not. The ECU is tuned via Flashpro and had been sent to Hondata to receive the modification to accept flexfuel and output boost control. Any other things to try to troubleshoot? Thanks!

 

I'm following up on this issue: it turns out it was my ECU. Plugging in the harness to the harness (where the primary and secondary oxygen sensors connect) can fry something in the ECU that pops a persistent, unclearable check engine light. The new ECU resolved the issue. I learned my lesson to not do it again; it's also opened my eyes that just because a plug is in the correct location and plugs right in doesn't mean that it should be plugged in. Consider this a PSA!

 

Unfortunately that's a sensitive set of connectors and it's imperative that you plug them in exactly where they should go as you discovered in your case...
Frying an ECU is no joke. I can only imagine.
Your PSA should help others

 

Yikes, how much did that cost? Thanks for the tip!

 

Another spot where connections can easily be plugged into the wrong spot is the center console. On cars with roof, hazard, and defrost, two connections are identical. Rule of thumb for center console is do not plug grey to grey.

 

Thanks for the tip; in general I'll need to be more careful about any situation where I disconnect/reconnect plugs.

The used ECU was about $200 on ebay, and I paid a local guy with the tool to come by my house and pair it to the car. I didn't need to reprogram keys or anything, but the ECU wasn't recognized until he did his thing, at which point I could re-flash the ECU with Hondata and start it up.

 

And how much did he charge for that?

 

He came by after he got off work and asked me to pay whatever I thought was reasonable. Since he made the trip I gave him $100, which I thought was fair for his time but cheaper than what it would have cost to have a dealer do it (plus at a dealer I wouldn't have been able to unpair/pair the ECU to Hondata and reflash). So a $300 mistake....

 

That's fair indeed

So how's your tune? Conservative, balanced or max power?

 

Relatively conservative, but with the 1,000cc injectors it wouldn't even start up without the flash. I had considered taking the time to put the fuel system back to stock and run no boost to take it to a shop, but this was a big time saver. with 93 octane the car makes 440whp at 15psi on a dynodynamics dyno.