Hello, I have a 2001 Honda Accord, 2.3L, 4 cyl, LX, 260,000 miles. It is running great, and if not for the check engine light I would not have thought there was an issue with it.

The P1166 and P1167 codes point to the o2 sensors, and I have already replaced both the upstream and downstream o2 sensors in hopes that would fix the CE light, but each time I clear the codes, when I start the engine again the CE light comes back on instantly, without any driving and without the engine idling for any amount of time at all. I was told by one person that this means it is a "hard code", since the CE light comes back on before the engine even has time to calculate any values of the running conditions (such as the fuel/air ratio at the o2 sensors, etc)...and the recommendation I got was to send the ECU in for testing since it may be a bad ECU.

I'm really hoping to avoid that, partly because of the cost, but also because I can't be without a car during that time. Again, the car runs great, so I have been continuing to drive it for the past week or so while I'm trying to diagnose it.

I was also told it could be a vacuum leak or a bad MAP sensor, but I could not find a vacuum leak, and after putting in a new MAP sensor and clearing the codes, the CE light came back on instantly the moment I started the engine. I also cleaned out the throttle bore about a month or two ago, so that should still be pretty clean (that was another suggestion I got).

I would greatly appreciate any suggestions for other things I could check or repair to possibly solve this issue!

 

Code reader? Need to put a scan tool on it.

 

Yes, the codes are P1166 and P1167. If I clear the codes and then start the engine, the CE light will come back on the instant the car is started, without driving or even letting it idle.

 

My point was you need to put a scan tool on it and see what's going on. You could check the integrity of the wiring.

 

I only have a basic code reader, but I have considered getting something more advanced, but not too expensive, like a ThinkDiag or something along those lines in the $100 range that can still do some advanced tasks and bi-directional functions, etc. It seems that going with a unit that connects to your phone or tablet (and therefore has no screen), gets you a lot more bang for your buck. Do you have any recommendations for a scan tool in that range?

 

The DTC P1166 and P1167 are codes for heater circuit of the upstream O2 sensor (air/fuel ratio O2 sensor).
The meaning is that the ECU sees a problem with the circuit.
You should check to see if there is continuity from the ECU to the O2 sensor
Also, check the fuse to O2 sensor. If the fuse is blown will also set code.

 

The fuse for that circuit is good, so I will check continuity from the ECU to the o2 sensor, but could you advise me on the steps to doing that? I have checked for the reference voltage at the o2 sensor, which was about 4 volts, but not sure how to check continuity from the ECU to the o2 sensor.