2008 Accord, downstream O2 sensors, constant voltage
07-22-2017, 06:36 AM
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2008 Accord, downstream O2 sensors, constant voltage
First, I recently changed my the original '08 3.5 J35 for one from a 2012. I left the '12 engine/trans harness on the '12 engine and its run great since swapping. (old engine seized both camshafts, pretty ugly.) If that wiring harness from the '12 is causing me issues, I can swap back to the '08, I'd just prefer not to. It's quite a bit of effort.
Ok, onto the issue. I've had a P0138 and P0158 code since swapping the engines, both downstream O2 sensors are new. I just figured out how to read live data and I monitored my readings from my downstream O2's. They're both constant, reading somewhere in the 1.1-1.2 range essentially from start-up onward. I know the reader is working because I monitored my wife's Avalon and they fluctuate between 0.4v and 0.7 depending on throttle input.
So, the first question is can anyone locate all the grounds associated with the engine harness? I've traced it back on the harness itself and there aren't many to locate. There is a big one under the air box that connects to a bracket on the trans and the chassis. Another pair of grounds near the engine hook by the power steering pump. One more on the engine mount near the power steering pump. Is there one back by the fuel line connections on the firewall, maybe by the ECU, etc? I sure seems like I'm missing a ground, honestly.
Second, I measured the voltage at the plug on the front bank, downstream O2 sensor. I get two with minor trace voltages, one with battery voltage, and the last with about 2.4 volts. Does this sound about right?
Any help is appreciated; its the only issue I have left on this car.
Ok, onto the issue. I've had a P0138 and P0158 code since swapping the engines, both downstream O2 sensors are new. I just figured out how to read live data and I monitored my readings from my downstream O2's. They're both constant, reading somewhere in the 1.1-1.2 range essentially from start-up onward. I know the reader is working because I monitored my wife's Avalon and they fluctuate between 0.4v and 0.7 depending on throttle input.
So, the first question is can anyone locate all the grounds associated with the engine harness? I've traced it back on the harness itself and there aren't many to locate. There is a big one under the air box that connects to a bracket on the trans and the chassis. Another pair of grounds near the engine hook by the power steering pump. One more on the engine mount near the power steering pump. Is there one back by the fuel line connections on the firewall, maybe by the ECU, etc? I sure seems like I'm missing a ground, honestly.
Second, I measured the voltage at the plug on the front bank, downstream O2 sensor. I get two with minor trace voltages, one with battery voltage, and the last with about 2.4 volts. Does this sound about right?
Any help is appreciated; its the only issue I have left on this car.
07-22-2017, 08:33 PM
#2
Re: 2008 Accord, downstream O2 sensors, constant voltage
If you're using the 2008's PCM and the 2012 engine wiring harness, the issue may be due to the PCM harness connector wiring for the sensor grounds to the secondary O2 sensor being different for a 2008 Accord vs. a 2012 Accord.
On a 2008, the sensor ground wires to Front Secondary O2 sensor (Bank 2 Sensor 2) and Rear Secondary O2 sensor (Bank 1 Sensor 2) is from PCM terminal no. C15 (PCM Connector C, terminal no. 15).
On a 2012, sensor ground wire to Front Secondary O2 sensor (Bank 2 Sensor 2) is from PCM terminal no. C36. Sensor ground wire to Rear Secondary O2 sensor (Bank 1 Sensor 2) is from PCM terminal no. C23.
So if you are using the 2008 PCM, the sensor ground wires for both Secondary O2 sensor would have to be switched to PCM terminal no. C15.
On a 2008, the sensor ground wires to Front Secondary O2 sensor (Bank 2 Sensor 2) and Rear Secondary O2 sensor (Bank 1 Sensor 2) is from PCM terminal no. C15 (PCM Connector C, terminal no. 15).
On a 2012, sensor ground wire to Front Secondary O2 sensor (Bank 2 Sensor 2) is from PCM terminal no. C36. Sensor ground wire to Rear Secondary O2 sensor (Bank 1 Sensor 2) is from PCM terminal no. C23.
So if you are using the 2008 PCM, the sensor ground wires for both Secondary O2 sensor would have to be switched to PCM terminal no. C15.
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