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2005 baja: 12 volts..disconnected..ignition switch..no voltage…

Customer Question
I'm working on a 2005...
I'm working on a 2005 baja, p0032 code, heater control high for o2 sensor. checked the connector at o2 sensor (vehicle side) and found 12 volts from main relay , went to ecm with o2 sensor reconnected , disconnected ecm connector, turned the ignition switch on and found no voltage on either if the 2 yellow wires at position 6 and 17, connector b136. I ohmmed out the yellow wires from the ecm connector to the o2 sensor connector, and they are good. If the heater was good, and the o2 sensor's connector was connected with the ecm connector disconnected, then turn on the key, I should get 12 volts on the 2 yellow wires, correct? What's acceptable resistance for the heater on the o2 sensor?
Submitted: 8 years ago.Category: Subaru
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Answered in 8 minutes by:
6/26/2010
Subaru Mechanic: Mike V., Subaru Technician replied 8 years ago
Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 27,776
Experience: Certified Subaru Technician, factory trained by Subaru.
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Chat Conversation Started
Carguy1 :

Hi there! You hjave to check the 2 yellow wires plugged in to the ecm. They should have more then 8 volts. You won't get voltage on them if they are unplugged from the ecm.

Carguy1 :

plug the ecm harness back in and back probe the #6 and #17 wires to check for power

Customer:

did that too. got 2.78 volts,.

Customer:

I thought they were the ground side of the circuit for the heater. unplugged I thought I' get the unused 12 volts from the main relay.

Carguy1 :

Ok, this was right out of the ecm? Any chance you have a scan tool that can read live data?

Customer:

At work, working on the misses car.

Customer:

checked the resistance of the heater of the o2 sensor and it was open at 2M ohms

Customer:

heater circuit looks like it's yellow and yellow with a red tracer.

Customer:

priced out o2 sensors, $150 -$ 200 . A little too expensive to see if I'm right.

Carguy1 :

Ok, here is my dilema, if you have less then 8 volts at pins 6 and 17, we are suppose to connect the scan tool. So, the problem is that it isn't telling me which wire to have you chack for amps from the sensor to the ecm. That being said,I would have you check the other pins at the O2 sensor to see what the amps are coming outr of the sensor. Basically what the code is saying, is the ecm is seeing no resistance in the heater. It is pumping the voltage into it and wants to see 2.3 amps coming out.This tells the ecm that the heater inside the sensor is using the voltage to heat up. Since you have checked resistance on the wires, I suspect that the sensor itself is no good.This is normally the cause

Carguy1 :

ok, so you need to check the amperage on the wires you suspect are the heater wires.

Carguy1 :

sorry, we were typing at the same time so I didn't see what you wrote

Customer:

what's the warranty? 2/24k?

Customer:

do you guys go through alot of these pre cat o2 sensors?

Carguy1 :

We do go through aloot of the front sensors. The warranty is 3/36 unless you have one of the extended warranty packages, then it might be covered

Carguy1 :

It is not unusual for the heaters to burn out

Customer:

the 2.78 volts I seen with the ecm connected must be generated by the ecm since nothing is coming through the heater, I should see really 12 volts shouldn't I.

Customer:

Are the owners doing anything wrong to cause the premature wear out of these parts?

Customer:

how many times have you changed the ecm after replacing the bad o2, sensor?

Carguy1 :

From what I am reading here it should be 12 volts coming out of the ecm on the Yellow wires to the O2 sensor.Because it is saying to repair the harness between the ecm and the O2 sensor if it is less then 12

Carguy1 :

See, it is not telling us to disconnect the ecm and check, it is telling us to check the ecm connector for the voltage.

Carguy1 :

I think the best bet at the moment is to check the other wires with the key on and see if one is producing the amps we are looking for

Customer:

Why would I repair the harness if the ecm connector is not got 12 volts, wouldn't the voltage come from the ecm. or does it come from the main relay on the power side of the heater?

Customer:

voltage going from the main relay to the sensor and back to the ecm?

Customer:

if a circuit has no path to ground then no voltage is used. hence i removed the connector, thinking the ecm gave the ground and monitorred the amp draw

Carguy1 :

Give me one minute to print the diagram,I will be right back

Carguy1 :

been a while since I did one of these is all

Customer:

I was thinking that 1 yellow wire was for the grounding and 1 yellow wire was for monitoring of the amps for the obd2 system.

Customer:

they're the thinner wires, the thicker are for the heater due to the current it uses?

Customer:

so, I've been on the right track. just needed confoirmation

Customer:

how often do you replace the o2 sensor to find it needs a ecm also?

Carguy1 :

I do believe you are on the right track. I also think if you check the red and white wire, you will find that one is producing to many volts or amps

Carguy1 :

Very uncommon. I think if I remember right, the only time this happened was in O2 on only a few legacys. The front sensor would go out and smoke the ecm at the same time. I think it 02 and it was only the manual 4 door sedan

Carguy1 :

It was bizzare to say the least that it would only happen to that model and only the manual 5 speeds

Carguy1 :

If you ohmed the yellow wires and they showed no shorts then I suspect they are good

Customer:

thank you, XXXXX XXXXX flow charts I got from ONDEMAND 5 from work truly sucked, truly vital pieces of info were missing like they said fix the harness, which meant possibly replaced o2 sensor for open heater

Customer:

and they left out if the connector needed to be disconnected and checked or connected and checked

Carguy1 :

I can tell you this,I am looking at the same stuff and it is right out of the Subaru manual word for word

Customer:

so I concentrated on the wiring diagram.

Carguy1 :

Yep, that is the way subaru does it

Carguy1 :

I can print you a page for this from the Subaru manual and it reads exactly the same

Customer:

for such nice cars they shouldn't do that to the service dept.

Customer:

must be lost in translatiion

Carguy1 :

and yes, this is how you learn to read and interprit the diagram, be cause the flow chart sucks!

Customer:

thank you, XXXXX XXXXX night

Carguy1 :

That's what I always figured as well. That is why school is so handy.

Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 27,776
Experience: Certified Subaru Technician, factory trained by Subaru.
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