Help with P0037 O2 heater code
07-06-2018, 07:33 PM
#1
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Help with P0037 O2 heater code
Hi there,
I have a P0037 O2 heater circuit low voltage code on my 09 LNF. I bought a new sensor, checked it, and the heater element is good. It is right around 10 ohms, which is fine. I then checked the voltage coming out of the engine harness. The plug was only pushing out 8.35V when battery voltage was at 12V, so clearly that is the cause of the code.
My next step is that I want to check the ECU and see if it is bad. I found that it is pins 7 and 23 on the right hand side ECU connector. When I unplug it, turn key to position 2, and probe the two pins with my multimeter, I get no voltage. Am I doing this step wrong? How am I supposed to check ECU voltage for the heater sensor circuit?
I know my last step is to check continuity of the engine harness from the ECU plug to the O2 sensor plug. I need to make an extension harness first so my multimeter leads can reach it. If everything is continuous, I guess I can narrow it down to only my ECU being bad. Am I thinking this through correctly?
I have a P0037 O2 heater circuit low voltage code on my 09 LNF. I bought a new sensor, checked it, and the heater element is good. It is right around 10 ohms, which is fine. I then checked the voltage coming out of the engine harness. The plug was only pushing out 8.35V when battery voltage was at 12V, so clearly that is the cause of the code.
My next step is that I want to check the ECU and see if it is bad. I found that it is pins 7 and 23 on the right hand side ECU connector. When I unplug it, turn key to position 2, and probe the two pins with my multimeter, I get no voltage. Am I doing this step wrong? How am I supposed to check ECU voltage for the heater sensor circuit?
I know my last step is to check continuity of the engine harness from the ECU plug to the O2 sensor plug. I need to make an extension harness first so my multimeter leads can reach it. If everything is continuous, I guess I can narrow it down to only my ECU being bad. Am I thinking this through correctly?
07-14-2018, 08:59 PM
#2
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Thread Starter
Ok, does anybody have tips on how to snake the harness through the engine back so I can easily test continuity? I have no clue where that loom splits off into, so I cannot pull the harness out.
07-15-2018, 12:20 AM
#3
pin 7 and 23 shouldnt have voltage between them. pin 23 and pin 38 are the oxygen sensor pins, pin 7 is the ground side of the heater, and voltage is supplied from the fuse. for this code the only pin at the computer you need to concern yourself with is pin 7.
07-15-2018, 11:34 PM
#4
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I tested the two white wires going into the O2 sensor and that is when I got 8.35V, so I'm guessing I was testing pin 23 and 38. I'm going to skip testing any ECU pins because of what you said.
I'm going to try and pull out the harness after removing the fusebox. I'll look for any chafing on the wires, and check continuity at pins 7, 23 and 38. Hopefully, I can see visible chafing and just fix that part of the wire.
07-16-2018, 12:50 AM
#5
pins 23 and 38 have ZERO to do with this code. test them if you want, but it means nothing to solving this code. you want to concentrate on the heater circuit, and thats pin 7 at the ecm to pin c on the 02 sensor, and pin d on the o2 sensor to the fuse block.
id check for battery voltage from o2 pin d to engine ground. best to do this while backprobeing the connector with the sensor hooked up, key on. if thats good, do a resistance test of the ground side between ecm pin 7 and o2 pin c.
looking at the diagram above there looks to be a connector between the sensor and the ecm, check there for corrosion. also have a look for any wire chafing or loose pins.
id check for battery voltage from o2 pin d to engine ground. best to do this while backprobeing the connector with the sensor hooked up, key on. if thats good, do a resistance test of the ground side between ecm pin 7 and o2 pin c.
looking at the diagram above there looks to be a connector between the sensor and the ecm, check there for corrosion. also have a look for any wire chafing or loose pins.
07-17-2018, 10:30 PM
#6
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Thread Starter
pins 23 and 38 have ZERO to do with this code. test them if you want, but it means nothing to solving this code. you want to concentrate on the heater circuit, and thats pin 7 at the ecm to pin c on the 02 sensor, and pin d on the o2 sensor to the fuse block.
id check for battery voltage from o2 pin d to engine ground. best to do this while backprobeing the connector with the sensor hooked up, key on. if thats good, do a resistance test of the ground side between ecm pin 7 and o2 pin c.
looking at the diagram above there looks to be a connector between the sensor and the ecm, check there for corrosion. also have a look for any wire chafing or loose pins.
id check for battery voltage from o2 pin d to engine ground. best to do this while backprobeing the connector with the sensor hooked up, key on. if thats good, do a resistance test of the ground side between ecm pin 7 and o2 pin c.
looking at the diagram above there looks to be a connector between the sensor and the ecm, check there for corrosion. also have a look for any wire chafing or loose pins.
I have confirmed than pin 7 to O2 pin C has 18ohms on my DVM. It matches resistance in pins 23 and 38, and yes I understand they do not apply to this code now. I use a cheap Harbor freight DVM in case the resistance looks high.
I’m a little lost on the terminology of the other wire. Backprobing pin D to engine ground means: with everything connected, one DVM lead in pin D and the other on a ground (like a bolt)? When key is in position 2, I’m guessing that should give me 12V? I don’t need to do anything with the fuse on the fuse block, right?
I’m looking for obvious wire chafing and I don’t see any. Pins don’t look corroded and none are loose. This is really stretching my knowledge but I’m glad I’m learning.
07-18-2018, 10:13 AM
#7
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Thread Starter
Ok so another update. I understand the backprobing after more Googling. Basically checking to see if there is any issue with the wire going into pin D by seeing how much voltage that wire is carrying. Well, battery voltage was 13.9v at the battery terminals and 13.9-ish volts at pin D to chassis ground. So that rules out any issue with that wire.
I am now guessing pin C is the culprit, even though it’s resistance is ok. I did read that testing resistance is less conclusive as even a small amount of resistance can cause a significant voltage drop. Again, when checking voltage between the two heater circuit wires (pin C &D) I only get 9.8v this morning. Guess I’m chasing a grounding issue now?
I am now guessing pin C is the culprit, even though it’s resistance is ok. I did read that testing resistance is less conclusive as even a small amount of resistance can cause a significant voltage drop. Again, when checking voltage between the two heater circuit wires (pin C &D) I only get 9.8v this morning. Guess I’m chasing a grounding issue now?
07-18-2018, 12:21 PM
#8
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Thread Starter
Last update from doing more backprobing now that I got the hang of it.
Pin C to ground I get 13.9-ish volts, which makes sense since my sensor is good.
Pin 7 to ground I also get 13.9-ish volts. So I get no voltage drop from that entire ground wire!
What. The. Heck.
Pin C to ground I get 13.9-ish volts, which makes sense since my sensor is good.
Pin 7 to ground I also get 13.9-ish volts. So I get no voltage drop from that entire ground wire!
What. The. Heck.
07-18-2018, 10:47 PM
#9
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Thread Starter
Last update.
Thanks to Sharkey, my probing around has fixed the car. I guess I knocked some dirt out of a connector and there's good connection everywhere again. I pulled swapped fuses and relays with others in the fuse block (didn't replace anything), and I probed everything. I also taped up the harness as the plastic wire loom was cracking apart. Whatever went on worked.
Drove it back from my parents garage to my place (~3 hrs) ready to take it to the dealer tomorrow. All readiness monitors (besides EVAP) are set so this thing is ready to go through inspection. Wow what a ride chasing this stupid code.
Thanks to Sharkey, my probing around has fixed the car. I guess I knocked some dirt out of a connector and there's good connection everywhere again. I pulled swapped fuses and relays with others in the fuse block (didn't replace anything), and I probed everything. I also taped up the harness as the plastic wire loom was cracking apart. Whatever went on worked.
Drove it back from my parents garage to my place (~3 hrs) ready to take it to the dealer tomorrow. All readiness monitors (besides EVAP) are set so this thing is ready to go through inspection. Wow what a ride chasing this stupid code.
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