Hello! This is my first post on a forum. I've repaired my own vehicles for many years. I have come across a CEL code I can't figure out. I'll do my best to describe what I've done over the last month. I own a 2001 Honda Accord 4-Cylinder 2.3L ULEV (ultra low emission vehicle). The emission system conforms to California standards. I've had three different codes over the past two months (P1164, P1166 & P1167) . I will concentrate on the recent prevalent code P1167. The best I can tell, this code refers to the upstream, Air Fuel Sensor heater element. I replaced the sensor with a Denso 234-9014 and still get the code within a couple of minutes at idle. Tested the four wires connecting the A/F sensor to the ECM. Disconnected the A/F sensor and the ECM wiring. Checked continuity of all four wires and verified no short exist between them or to ground. Check the heater resistance of the original A/F sensor and it measured 20.5K ohms. Searching online, it appears the resistance for a LEV is 10-40 ohms and a ULEV is 2-20 ohms. The new A/F sensor measured 1.2 ohm. Thought this was low, purchased another from a different source and it was also 1.2 ohms. Does this sound normal? Ran the car with the A/F sensor connected but not installed (another one was installed) and the sensor got warm to the touch until the code popped up and there was no voltage/power to the heater element. To test the heater element drive circuitry, I modified a sensor by cutting the two black heater wires and replace the heater element with a 1156 auto light in series with a 10 ohm resistor (~11ohms). Started the car, reset the CEL code and the 1156 light illuminated and cycled on/off very quickly. This should have been a good representation of the heater element. Guess what, after a few minutes the code returned. Purchased and installed a replacement ECM with the same exact part number along with the immobilizer circuitry. Started the car and tested with the new 234-9014 sensor, it's back, the code returned. Tested with the original A/F sensor... the code returned.

Read elsewhere online it could be the Mass Air Flow Sensor. This doesn't seem to make sense to me, so here I am asking for your help.
I have run out of ideas and spent way to much time into this vehicle (my son's college commuter vehicle). Any response or suggestions would be appreciated.
Thanks in advance.

 

I neglected to mention that the fuses (drivers side and passengers side) have been checked, once by my son and once by me. All are good. Would having a real time OBDII reader help diagnose this issue? If so, any recommendations, maybe an Actron CP9680 autoscanner?

 

The "new member" area is mostly for welcome & introductions, so I'll move this to General Tech. More people will notice it there.

I don't think I would worry a lot about 1.2 vs 2 ohms. When the resistance is that low, a normal handheld multimeter isn't the most accurate.

 

Whenever a code comes up for a "sensor", the root cause can be the sensor, the wiring/electrical, or the PCM. Since the sensor and PCM didn't fix the problem, the next step is wiring.

Did your new A/F sensor come with an electrical connector, or did you have to wire it yourself?

 

Both A/F sensors that I have tested, Denso 234-9014, were purchased with the electrical connector pre-wired.

 

You almost narrowed down the problem to the wire harness based on replacing the sensor and PCM. Plus the other electrical codes for the A/F sensor you've had in the past.

Did anything happen to the car (accident, repair, maintenance work, etc.) right before you started getting this code?

As for tools, the best purchase you can make for diagnostics is the OEM shop manual. You can get a pdf for the 98-02 accords for $22 at automanualsource.com. It is definitely money well spent.

 

Thanks for the reply. Now that you mention other work done... About 2 months ago, we replaced the front bumper and the codes started right about then. The bumper was change due to a very slow (5mph) minor accident of hitting a trailer hitch and cracking the bumper. The replacement didn't require any rewiring or disconnection of lights/connectors. At the time, I thought it may have something to do with the code, so we did reinspect our work, although couldn't find anything wrong.

Is there any additional measurement that could shed some light on why the PCM is throwing the code? Would a diagnostic tool show the live data causing the code to be set? How about the current to the A/F heater, is it too much/ too little? I have tried different resistors (2, 10, 12, 30 ohms) to simulate the heater element to no avail.

I just purchased the OEM shop manual. Thanks!

 

I have downloaded the OEM shop manual. There's lot of valuable information in there although I haven't located a wiring diagram/schematic for the emission system including the A/F sensor. Am I just overlooking that information?

 

Go to the "Fuel & Emmissions" section.
If it's the same manual I have, the circuit diagram is titled as the "ECM/PCM Circuit" but it really includes all the sensors connected back to the PCM. It looks like it's in 2 different pieces; one starts about page 11-13 & the other about page 11-33 or so.

And there's a table near the beginning of section 11 with each fault code and where to go for it's troubleshooting procedure.

 

Thanks Jim. That's the info I was looking for.

The one item I haven't check is the A/F relay. Do you know how and/or when the A/F relay is used?
If I can locate the relay, I will check the contacts for N/O and N/C as well as the coil for continuity (if same type is available, swap it).
Next on the list is conducting the test for P1167 (again) and P1166. I've run out of other things to try.
Any advice/suggestions?