I am looking for insight on an issue I am having with a 97 Integra GSR I have been working on. I purchased the car as a theft recovery that was missing the cluster, ecu, and seats. I replaced the ecu and cluster with the correct GSR cluster and a known good OBD2A P72 ecu I had laying around. It runs fine, but as soon as I turn the key to the on position a cel comes on for a primary O2 sensor heater circuit issue. I have tried:
- replacing the primary O2 sensor with a new one
- using a jumper harness and OBD1 P72 ecu
- checking all connections at the ecu and shock towers
- cleaning and inspected all grounds
- following the wiring and inspecting it from the ecu through the firewall to the passenger side shock tower
- checking continuity from the ecu to the shock tower and from the shock tower to the O2 sensor
- pulling and dissecting the complete engine harness, looking for issues, and taping/looming it all back together correctly
- properly removing an old security system (figured you never know)

I am not one to ask for help, but I have this car sold, and I need to get it done before I leave for Florida on Wednesday, June 25th. If anyone has any ideas that they have personally found helpful in this situation, or if anyone knows the proper way to bypass the harness and run a wire directly from the ecu to the sensor, I would greatly appreciate your input. Thanks in advance!

 

Did you use a bosch sensor? Or...anything besides NGK or Denso?

 

I tried 3 used OEM sensors first, then I did use a new Bosch as that is all anyone and in stock in my area.

 

What is the exact code?

 

OEM like stock NGK/Denso or OEM the brand?

I ask because I kept getting a code 67 for secondary circuit heater. Tried a new Bosch sensor because I had one laying around. Same code popped up. I checked the resistance and got a value that was just underneath the acceptable limit for heater circuits. I thought "maybe this meter is a bit off or something. The sensor is brand new!"

I was elbows deep in wiring diagrams amd diagnostics when I decided to try a used NGK sensor. The resistance came up within tolerance for that sensor.

As soon as I did, the code vanished.

 

P0135 - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1

 

 

Looks like a ton of fun...I will attempt this tomorrow. Thank you for the info!

 

After using the steps above I narrowed it down to a bad ecu. Oddly enough I tried an OBD1 P72 with a jumper harness before and it threw a cel, but when i reinspected that ecu I found that a pin was bent and not making contact with the jumper harness completely. I wish I would have noticed this two days ago…Oh well! Thanks for your help HondaPartsHero!

 

Factory service manuals, gotta love em.