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Hey guys, I have an 03 OBW 4cyl. tripped CEL last week. Said p0030__E1 heater control circuit bank 1 sensor 1. I think car had original O2 sensor so just bought a new Denso 234-9015 upstream unit then replaced.I did do the front sensor, bad place to get out of, dropped front pipe made sure elec connection was solid. I don't see any corrosion on pins.
Cleared codes, all good for a few days. Yesterday CEL went back on, same code. Not funny. Car needs to go to inspection in the next month.
I did some testing of OLD unit across 3-4 term. opposite side of lock tab- res says 2.4 ohms. not sure what is normal- I think I read 3 ohms. NEW unit says about 2 initially then quickly drops to about 1.8ohms. Something seems wrong.
I'm not sure if I need to send unit back.
Old unit definitely tired, car runs much better but need some resolution.

Thanks in advance, Eric
 

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Hey guys, I have an 03 OBW 4cyl. tripped CEL last week. Said p0030__E1 heater control circuit bank 1 sensor 1. I think car had original O2 sensor so just bought a new Denso 234-9015 upstream unit then replaced.I did do the front sensor, bad place to get out of, dropped front pipe made sure elec connection was solid. I don't see any corrosion on pins.
Cleared codes, all good for a few days. Yesterday CEL went back on, same code. Not funny. Car needs to go to inspection in the next month.
I did some testing of OLD unit across 3-4 term. opposite side of lock tab- res says 2.4 ohms. not sure what is normal- I think I read 3 ohms. NEW unit says about 2 initially then quickly drops to about 1.8ohms. Something seems wrong.
I'm not sure if I need to send unit back.
Old unit definitely tired, car runs much better but need some resolution.

Thanks in advance, Eric
I have the same problem on my 03 Outback. From what I've read anything less than 5 ohms on pins 3/4 means you should have a working O2 A/F sensor. What is strange is I had been using a Bosch O2 and did not have any engine warnings.

I bought a new Denso 234-9015 sensor hoping it would improve my gas mileage, but sure enough within three times driving the Suby the check engine light came back on (P0030). I too checked pins 3/4 (O2 heater circuit) and had 1.8 ohms and a strong 12V with the key on. The good Bosch O2 had the same 1.8 ohms. I'm baffled, hopefully we can get some input from the experts to help us figure this out. :unsure:
 

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I've read anything less than 5 ohms on pins 3/4 means you should have a working O2 A/F sensor.
It means that the connections from the connector through the sensor heater are intact. The sensor itself is separate and could have problems of its own.

within three times driving the Suby the check engine light came back on. .
Normal. That code will trigger the CEL if the fault is detected in two consecutive driving cycles.

I too checked pins 3/4 (O2 heater circuit) and had 1.8 ohms and a strong 12V with the key on.
Was the 12 V measured with the key at On but engine not started, or started? Where was the 12 V measured?

Attached might be of help.
 

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It means that the connections from the connector through the sensor heater are intact. The sensor itself is separate and could have problems of its own.


Normal. That code will trigger the CEL if the fault is detected in two consecutive driving cycles.



Was the 12 V measured with the key at On but engine not started, or started? Where was the 12 V measured?

Attached might be of help.
The 12V was measured with the key on without the engine running
 

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Was the 12 V measured from the sensor harness connector pin 4 to ground? If not, then where was it measured?

Have you checked the wiring between the sensor connector, pin 3 and and the ECM pins C16 and C17, as set out in the previously attached diagnostic page?

The P0030 is triggered when a continuity or short circuit fault is detected in the heater "control circuit", That includes both the heater in the sensor and the wiring to it.

The 12 V at sensor connector pin 4 (measured to ground) confirms that there's a connection from the main relay to the sensor connector (at pin 4). That leaves the connection from the sensor heater to the ECU.
 

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Yes to "12 V measured from the sensor harness connector pin 4 to ground". I wiggled the wire loom to see if the voltage changed, but it was solid.

Have you checked the wiring between the sensor connector, pin 3 and and the ECM pins C16 and C17, as set out in the previously attached diagnostic page?
Would this be a continuity test with a VOM on testing the wires, will this test the grounding of the circuit?
 

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Would this be a continuity test with a VOM on testing the wires,
Yes.
Steps 1 and 2 in the troubleshooting paper are for continuity of the heater control connection, and the connections for the O2 sensor itself.
Step 3 checks the continuity of the wire from the relay to the sensor heater.
Step 4 checks the continuity of the wires to, and through, the heater itself.

will this test the grounding of the circuit?
Not sure what you mean "grounding of the circuit". The ECM has grounds (as shown in the wiring diagram). These can be checked for continuity as well.

When doing steps 1 and 2, after verifying the continuity of each wire, the VOM can be used to check for a short between the wire and ground (there should be no continuity, i.e., open circuit, between the wire and ground).
 
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