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No reading on upstream o2 sensor ~ MPG

4K views 11 replies 2 participants last post by  Bojango 
#1 · (Edited)
I am trying to diagnose gradually worsening mpg, and was looking at the o2 voltages with my scan tool. I am only getting a reading for Bank 1 Sensor 2, which is the downstream o2 sensor correct? The fact that there is no reading for the upstream o2 means it is obviously dying/dead, yeah? These checks were done during 20-25 minute drives for warmups. ECU claims to move to close loop after warm up.

I want to check in with this before I move to the rest of the troubleshoot list

Current mpg:23 Before drop: 30 ; no CEL
 
#2 ·
Your right to look at the engine parameters first, strange no reading on a/f sensor.
Does it show up when scanner used on another vehicle?
Can you see other PIDs? LT/ST fuel trims at idle and then at higher RPMS(hold at 3000 for 30 sec or so for LT to read correctly).
Look for combined positive/negative LT/ST fuel trims to stay under 10.
 
#3 ·
For clarification; I am getting an A/F ratio reading among other PIDs , I was talking specifically about the o2 sensor voltages. In the mean time, I will report back with fuel trim and a/f ratio. Should I still try to test scanner in diff vehicle?
 
#5 ·
Ah yes, that makes sense regarding the sensors

My ST LT fuel trims are:
  • Idle LT: -6.2 to -3.1 %
  • Idle ST: 0 to 1.6 %
  • 3k LT: -2.3 %
  • 3k ST: 1 to 1.6 %

AFR commanded and measured at 14.7

Looks ok to me? If you agree I will proceed with my troubleshoot list I have gathered from other threads
 
#10 ·
With car on jacks, I am able to get roughly half a rotation on the front wheels, while on the rear I can get 2 rotations with the same amount of force applied with my hand. The threads I read about disc brake drag seem to be subjective on the amount of drag that is acceptable, as the pads are supposed to touch rotor anyway.

Slider pins etc may need a regrease? Without taking apart the calipers, they look healthy and pads have plenty of life
 
#11 ·
You may try using a temp gun on the brakes. This would test brakes/bearings for any undue heat buildup.
Don't have specific temps you'll have to do some comparisons.

The tire rotation tests sounds right maybe apply brakes a few times between rotations to verify pads returning to normal.

Other possibility transmission slipping/TC not locking up.
Trans fluid has been changed last 30,000?
 
#12 ·
My last two tanks are back up to 31 & 29.5 mpg, but those were 100-90% highway. The tanks before were all about 70% hwy. I will report back on my next 70% hwy tank.

The ideas from your last post weren't yet tried, so who knows. I will be keeping them in mind for future reference as well.
 
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