P0155, P0171 and P0125 SOLVED (1 Viewer)

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BullElk

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Just an FYI in case it may help someone as they search.

‘99 LC 465 k miles. I have been having all three of these codes come up. Two codes showing system running too lean on each bank and P0125 coolant temp code as a result of the first two codes… so says my research.

I changed sensors, new coolant temp sensor and cleaned MAF. Codes still present.

Then I changed the fuel filter. Codes haven’t come back yet. The brown fuel coming from filter might just have been an issue and proof of a good working filter.

Hope this continues to be the solution for mine and any others.
 
Hope this continues to be the solution for mine and any others.
Well it Ain't!!! Dagnabit!

All three codes are back. Changed PCV valve, fuel filter, MAF sensor, O2 sensors, coolant temp sensor see no signs of vacuum leaks and still bank 1 sensor 1 running lean and bank 2 sensor 1 heater circuit issue.

Any suggestions of what to look for as I continue to search?

Thanks
 
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You’ve done what I would do so far. The coolant temp sensor would have been my first thought after validating there are ZERO vacuum leaks.

Have you traced the wiring as much as possible to verify no bare wires and everything is intact?

Edi: can you view your engine data stream and do any of the tests in tech stream?
 
Have you traced the wiring as much as possible to verify no bare wires and everything is intact?
I have verified O2 wires are good. Haven't looked at any other wiring that isn't obvious I just read where a problem with bank 2 sensor can trigger the "generic" code p0171 on bank 1. I have a cheaper sensor in bank 2 and denso in bank 1.....for now.
 
You could for kicks swap the o2 sensors side to side and see if anything changes or if code follows.
 
I just noticed a bit of oil ? residue coming from back corner of intake manifold seem. Cleaned it off and was able to tighten up two bolts there. No other areas around intake has residue nor loose bolts. Although extremely small air crack, perhaps that is the code culprit. No idea why those bolts would loosen unless Berryman B12 or Marvel mystery oil would eat the gasket away.
 
When my coolant temp sensor went bad, I changed the coolant temp sensor twice with no luck. In the end it was the harness to the temp sensor that was also fried a bit. I cut back 2-3" of the harness, new plug and new sensor and problem solved.
 
When my coolant temp sensor went bad, I changed the coolant temp sensor twice with no luck. In the end it was the harness to the temp sensor that was also fried a bit. I cut back 2-3" of the harness, new plug and new sensor and problem solved.
How did you know your temp sensor was bad? a code?, inaccurate temp reading?
 
How did you know your temp sensor was bad? a code?, inaccurate temp reading?
A code, at the time I was getting a bad temp sensor code and an 02 sensor code. I replaced the driver's side forward 02 sensor and temp sensor along with new harness plug pigtailed in. I still have a 2nd 02 sensor on hand that I did not install on passenger front side as the code went away after sensor replacements mentioned and has driven fine since. This was about two yrs ago.
 
I’m hesitant to say but…I took out cheap B2 S1 and checked ohms. I didn’t get any reading at all. Replaced with new Denso reading 16 ohms.

All day yesterday had no CEL, no code, no pending code. And no issues so far this morning as I’m off efforting towards arrowing wild swine.

I read where the p0155 from B2S1 can trigger the lean code P0171 from B1S1. So far I believe it.
 
When my coolant temp sensor went bad, I changed the coolant temp sensor twice with no luck. In the end it was the harness to the temp sensor that was also fried a bit. I cut back 2-3" of the harness, new plug and new sensor and problem solved.
I changed my ECT sensor yesterday and the harness clip snapped off so now I need to do what you did. Any chance you have a part number for the harness sensor you spliced in?
 
I changed my ECT sensor yesterday and the harness clip snapped off so now I need to do what you did. Any chance you have a part number for the harness sensor you spliced in?
NewYall Engine Coolant Cooling Water Temperature Temp Sensor Switch Connector Plug Pigtail Wire https://a.co/d/aPuUiaz


I wrapped the pigtail generously with electric tape to proved more insulation.
 

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