My son has a 2004 Accord V6 with a/t. Recently, his CEL came on so he took the car to Autozone. After reading the codes, they printed out 2 'receipts' that gave the definition of the code and listed probable causes.

The 2 codes that were identified were PO135 and PO155. Both codes indicate a heater system malfunction. However, according to the printed receipts, it appears there may be 2 different sensors involved....sensor 1 (PO135) and sensor 21.

I don't want to throw away money replacing o2 sensors needlessly and I'm not sure which sensor(s) is the culprit...if at all.

I'd really appreciate your thoughts on whether I need to replace 1 or 2 oxygen sensors. Which one? Part # ??? Denso?

In the past, I successfully performed a DIY replacement of an o2 sensor on a 1997 Toyota Avalon which was located near the firewall. Not too bad of a job. How difficult will the job be on my '04 Accord???

P.S. I tried to do a search of this forum typing in oxygen sensor and PO135 and PO155 but it was unsuccessful saying nothing was found. Sorry if I'm breaking any forum rules but I am trying to be compliant. Thanks very much for your help!!!!!!

 

Check for blown fuse(s) and connections first. It can be the fuse(s), poor connection or loose terminals.

The V6 has 2 air fuel ratio sensors and 2 secondary oxygen sensors.

P0155, Bank 2, Sensor 1; looking from the front of the car, is the A/F ratio sensor is in FRONT (radiator side).

P0135 is Bank 1, Sensor 1; looking from front of car, is the A/F ratio sensor in BACK.

The front A/F ratio sensor is Honda part # 36531-RCA-A02.
The rear A/F ratio sensor is Honda part # 36531-RDV-004.

The Denso cross reference number for both are the same part # 234-5010.

From what I heard from a Honda mechanic, the two A/F sensors are the same.
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This is an excerpt of Honda troubleshooting procedures:

DTC P0135: Rear A/F Sensor (Bank 1, Sensor 1) Heater Circuit Malfunction

NOTE:
Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information.
Information marked with an asterisk (*) applies to the front bank (Bank 2).
Turn the ignition switch ON (II).
Clear the DTC with the HDS.
Start the engine.
Check for Temporary DTCs or DTCs with the HDS. Is DTC P0135 and/or P0155* indicated? YES - Go to step 5. NO - Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the A/F sensor (Sensor 1), the A/F sensor relay (LAF), and the PCM.
Turn the ignition switch OFF.
Check these fuses:
No. 19 OPTION (40 A) fuse in the under-hood fuse/relay box.
No. 4 A/F SENSOR (15 A) fuse in the under-dash fuse/relay box.
No. 23 IGP (7.5 A) fuse in the under-dash fuse/relay box.
Are any of the fuses blown?

YES - Repair short in the wire between the A/F sensors, the A/F sensor relay (LAF), and the fuses, then go to step 24.

NO - Go to step 7.

 

Search again - the code numbers are P0135 & P0155. Second digit is ZERO not the letter "O".

Since they both come up, the first thing I'd do is rule out a common problem like the fuse that powers the heater circuits.

Each cylinder bank of the V-6 has it's own exhaust catalyst. These sensors are ABOVE the catalyst, one in front & one back to the firewall.

Unplug each one and look at the sensor-side of the wires. Two wires will be the same color (black?) and you can measure resistance between them. (Got a multi-meter?) I think it should be 2.1 to 2.9 ohms. If those are OK then the problem can be in the car's wiring.

Look for dirty/loose/corroded pins where you unplugged them. Look for pinched or torn wires going back into the car's wiring harness. Stuff like that...

 

Aftter researching the questions and the answers for
accordian 04 I see that both men have hit the nail on the head as usual..
Thank You Jimblake and Redbull1 for the good answers for his questions..

To the poster..use the OEM o2's when replaceing yours..they will then have the same values...

WheelBrokerAng

 

It can also be the air/fuel ratio sensor relay, see attached pic. for location. The A/F ratio sensor relay can be tested, I included the instructions for testing 4-terminal type relays.

 

Thank y'all so very much. It really helps knowing the difference between a zero and the letter "O" when searching. I had no idea...so thanks for pointing that out. Sorry for my mistake!

Apparently, an air/fuel ratio sensor and an OXYGEN sensor (as I refer to it) are ONE in the SAME???

I'm not the sharpest tool in the box (obviously) ...but I'll re-read all of your posts and try to follow the troubleshooting guide (although I'm not sure what all your acronyms stand for). Hopefully I'll get through it.

Just a point of information, about 2 month ago, I was going to change spark plugs and went so far as to remove the plastic engine cover to gain access to the front bank of plugs. After loosening the 2 screws, I tried to remove the cover but something was preving it's removal. While wiggling the loosened cover (using some gentle 'force'), I noticed a plastic clip was prohibiting its complete removal.

During the 'wiggling of the cover', I suppose I could have 'disturbed' or bumped the wiring to the front "oxygen sensor" causing my CEL problem. Perhaps shorted some wiring??? Disturbed the connection??? IN FACT, it was IMMEDIATELY after this aborted attempt to change plugs and the possible disturbance to the front o2 sensor that the car displayed the CEL. Does this information help make your diagnosis a bit more conclusive??? If so, what should I do???

Thank you ALL for your rapid, thorough, and throughtful replies.

 

Yeah, that makes sense. Certainly, you can remove that cover again and look for problems with the wires leading to those sensors.

Say that you pinched the wires, they shorted and blew their fuse. Then both O2 sensors would display those error codes that you got. Change the fuse & it blows again, UNLESS you fix the pinched wire first. Maybe the wire isn't pinched - maybe the insulation is rubbed off or something else. You gotta figure that out.

And...
"Normal" oxygen sensors have a very narrow band - they're kinda like an "on-off" switch. The computer keeps hunting around the point of switching on & off.

Wide-band oxygen sensors have a wider proportional measuring range, so they can be used (by a more sophisticated controller) to give a smoother, more accurate control of air/fuel ratio. Honda calls this a "air/fuel ratio sensor".

So I have a tendency to call them both "oxygen sensors". When buying a replacement, you really have to get the right kind to go along with the programming of your engine controller.

 

Some of Redbull's acronyms...

DTC = diagnostic trouble-code (P0135 or whatever number you get)

HDS = Honda diagnostic system - that's Honda's proprietary scanner that can do a lot more than the scanner you borrow at AutoZone. It can command your car to do other stuff, program the immobilizer for new keys, read error codes for the ABS & ventilation systems in addition to the engine codes.

PCM = powertrain control module - most people call this the ECU - it's the engine & transmission control computer.

 

Just an update on my situation. This past weekend, I looked at fuses #4 (15A) (LAF) which protects the a/f sensor RELAY. It was good!!! I also looked at fuse #23 (7.5A) (fuse name IGP) which protects A/C diode and a/f sensor RELAY. It was good. As I'm sure you know, these fuses are located under dash. However, I did NOT perform an inspection or test of the RELAY itself. To access the relay (under dash), I needed to remove a panel that my tired old eyes could not see how to do. NOTE: It was 105 degrees and the sweat was burning my eyes and clouding my bifocals.

After confirming the two fuses were good and inspecting the wiring related to the a/f sensor (it appeared to be in good shape), I decided to replace the upstream sensor (a/f sensor) itself...the one nearest the radiator which I believe is referred to as Bank 2, Sensor 1. (As I told you, I disturbed the sensor wiring when attempting to change spark plugs leading me to believe I damaged the sensor). FYI...disconnecting the sensor at the plug-in was a TOTAL PITA and I still don't know how I did it.

After installing the new a/f sensor, I started the car and the CEL was still on, so I made a trip to Autozone to clear the codes so the CEL light would 'go-away'. After 2 days of driving the car, the CEL is now back ON. I took it back to Autozone to read the codes. NEW CODES ARE P0134 and P2237. WHAT SHOULD BE MY NEXT STEPS??? I'm beginning to feel as though I needlessly spent $130 on the new a/f sensor bought at the Honda dealer.

Another point of info...I mentioned this nightmare of the CEL coming on began about 1 month ago. It all began immediately after starting the car following my aborted attempt at changing the spark plugs. I mentioned how I gently disturbed the wiring to the a/f sensor trying to remove the plastic access cover to the front 3 spark plugs (I didn't realize the a/f sensor wires were clipped to the cover). WHAT I DIDN'T MENTION is the battery was dead when trying to start the car (my son left the interior light ON overnight and into the following day). So, I connected a battery charger to the battery for a short time (15 minutes) in order to get the car started. This is when the CEL 1st appeared. I'm NOW beginning to wonder if these codes I'm experiencing (first the P0135 & P0155 and NOW the P0134 and P2237) are the result of using the battery charger???

HELP!!!!!!!!!!!!!! Thanks for your input.

 

The P2237 and the P0134 point towards Bank 1, sensor 1. So we should be looking at the rear O2 - engine and firewall.

I would have the battery tested and be sure the cable ends are clean and tight. A failing battery or loose connections can/do cause all kinds of strange things.