O2 sensor wiring help
Thread Starter
5 Year Member
Joined: Mar 2019
Posts: 23
Likes: 6
From: California
O2 sensor wiring help
Having some trouble with Bank 1 O2 sensor wiring and looking for some advice and help!
Truck is a 2004 F150 Heritage (looks like a 2003) 7700 - dedicated compressed natural gas with the 5.4 Only 49k miles.
Truck runs rough during the 1st start of the day. The longer it sits, the rougher it runs.
After 10-20 min or so it will run perfect.
I've replaced all cops, plugs, 02 sensors, air filter, cleaned MAF, cleaned injectors with PM-5, changed coalescing filter (like a fuel filter for CNG vehicles) changed oil, Checked for vacuum leaks. Fuel trims look good.
Ran the Torque app and noticed that Bank 1 O2 sensor is slow to respond and start switching. Bank 2 switches pretty quickly after startup.
Only after the truck is totally warm will Bank 1 start switching. It once threw a P1131 code.
Suspected that Bank 1 O2 sensor wasn't heating up so I busted out the multimeter and followed this guide:
https://troubleshootmyvehicle.com/fo...eater-test-2#2
When testing the red/white wire of the wiring harness connector, Bank 1 did not register the 10-12 volts while Bank 2 did.. so I think I found the culprit.. just don't know the fix.
According to this, it looks like that red/white wire runs to #93 of the PCM:
https://troubleshootmyvehicle.com/fo...iring-diagrams
I've got to admit I'm lost here and have no idea how to check the PCM side. Does anyone know?
I'd love to check out the wiring harness connector better but it's really wedged up there.
Any other good spots to check? Any other advice is greatly appreciated. I really love this truck and just want it to run as good as I know it can!
Truck is a 2004 F150 Heritage (looks like a 2003) 7700 - dedicated compressed natural gas with the 5.4 Only 49k miles.
Truck runs rough during the 1st start of the day. The longer it sits, the rougher it runs.
After 10-20 min or so it will run perfect.
I've replaced all cops, plugs, 02 sensors, air filter, cleaned MAF, cleaned injectors with PM-5, changed coalescing filter (like a fuel filter for CNG vehicles) changed oil, Checked for vacuum leaks. Fuel trims look good.
Ran the Torque app and noticed that Bank 1 O2 sensor is slow to respond and start switching. Bank 2 switches pretty quickly after startup.
Only after the truck is totally warm will Bank 1 start switching. It once threw a P1131 code.
Suspected that Bank 1 O2 sensor wasn't heating up so I busted out the multimeter and followed this guide:
https://troubleshootmyvehicle.com/fo...eater-test-2#2
When testing the red/white wire of the wiring harness connector, Bank 1 did not register the 10-12 volts while Bank 2 did.. so I think I found the culprit.. just don't know the fix.
According to this, it looks like that red/white wire runs to #93 of the PCM:
https://troubleshootmyvehicle.com/fo...iring-diagrams
I've got to admit I'm lost here and have no idea how to check the PCM side. Does anyone know?
I'd love to check out the wiring harness connector better but it's really wedged up there.
Any other good spots to check? Any other advice is greatly appreciated. I really love this truck and just want it to run as good as I know it can!
5 Year Member
Joined: May 2015
Posts: 4,178
Likes: 1,208
Truck shouldnt run rough in open loop mode either
So you might have an O2 problem, but its not your main problem imo.
Vehicles run fine in open loop, just not as fuel efficient.
What does LT fuel trim on that bank look like when sensor is warmed up?
So you might have an O2 problem, but its not your main problem imo.
Vehicles run fine in open loop, just not as fuel efficient.
What does LT fuel trim on that bank look like when sensor is warmed up?
Last edited by mbb; Mar 27, 2019 at 02:04 PM.
98 F150 5.4L E40D/4R100
Joined: Nov 2006
Posts: 28,520
Likes: 7,631
From: MI
On the O2 harness itself, the two whites are the heaters, the black wire is signal and the grey is direct PCM ground. The PCM is in charge of grounding with these vehicles. Hope that helps in some way lol.
Thread Starter
5 Year Member
Joined: Mar 2019
Posts: 23
Likes: 6
From: California
Thanks for all the help and advice fellas!
It currently isn't running well in open loop mode, so something is up with this truck!
If I unplug the battery long enough for a reset, it will run nice and smooth the next morning. Every day after that, it gets progressively worse and worse. The longer the truck sits and the colder it is, the worse it seems to run.
So today, I made a video of the 02 sensors and LT fuel trims and found you are correct!
LT fuel trims are all over the place and the truck is jumping in and out of open/closed loop and only reading from Bank 2 O2 sensor for almost 20 min after startup.
Here's a brief run down:
1:57 - Truck finally entered closed loop - Fuel trim shoots up to 25%
2:27 - Goes into open loop again
2:25 - Closed Loop again.. but only operating off Bank 2 O2 sensor
9:25 - Bank 1 O2 sensor spikes and falls - Bank 1 fuel trim up to 25%
23:00 - Both O2 sensors are finally fully active & switching the truck is running great.
Sincerely appreciate any guidance anyone has on this one.. been throwing a lot of time, parts and money at this problem and haven't found the fix yet.
Many thanks in advance!
It currently isn't running well in open loop mode, so something is up with this truck!
If I unplug the battery long enough for a reset, it will run nice and smooth the next morning. Every day after that, it gets progressively worse and worse. The longer the truck sits and the colder it is, the worse it seems to run.
So today, I made a video of the 02 sensors and LT fuel trims and found you are correct!
LT fuel trims are all over the place and the truck is jumping in and out of open/closed loop and only reading from Bank 2 O2 sensor for almost 20 min after startup.
Here's a brief run down:
1:57 - Truck finally entered closed loop - Fuel trim shoots up to 25%
2:27 - Goes into open loop again
2:25 - Closed Loop again.. but only operating off Bank 2 O2 sensor
9:25 - Bank 1 O2 sensor spikes and falls - Bank 1 fuel trim up to 25%
23:00 - Both O2 sensors are finally fully active & switching the truck is running great.
Sincerely appreciate any guidance anyone has on this one.. been throwing a lot of time, parts and money at this problem and haven't found the fix yet.
Many thanks in advance!
Last edited by Squeezsh; Mar 28, 2019 at 04:09 PM. Reason: video links
Thread Starter
5 Year Member
Joined: Mar 2019
Posts: 23
Likes: 6
From: California
So I finally got this one solved.. Many thanks to all the great suggestions. Cluing me into the fact it should run good in open loop was a great lead.
It ended up being dirty/plugged up injectors.
Truck would run rough upon cold startup.. The colder it was the worse it would run.
After driving it about a mile or so and giving it some aggressive throttle input it would clear up and start to run well.
since it seemed temperature dependent, I busted out the heat gun and carefully warmed up the injectors on a cold morning... That did the trick and helped me isolate the issue to the injectors.
I removed then and brought them to RC Fuel Injection in Torrance, CA.
I'm not a paid endorser or anything.. but that place is great. Quick turnaround and reasonable prices.
Truck is starting perfectly now and running great.
Hope this helps anyone with cold start issues.
It ended up being dirty/plugged up injectors.
Truck would run rough upon cold startup.. The colder it was the worse it would run.
After driving it about a mile or so and giving it some aggressive throttle input it would clear up and start to run well.
since it seemed temperature dependent, I busted out the heat gun and carefully warmed up the injectors on a cold morning... That did the trick and helped me isolate the issue to the injectors.
I removed then and brought them to RC Fuel Injection in Torrance, CA.
I'm not a paid endorser or anything.. but that place is great. Quick turnaround and reasonable prices.
Truck is starting perfectly now and running great.
Hope this helps anyone with cold start issues.