Live data reader interpretation

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
My 98 D1 (AEL) threw a P0138 code, corresponding to driver's side downstream O2 sensor. Curious about what's happening, I checked the live data on my TurboGauge (a knockoff ScanGauge) and saw some fuel trim numbers that looked out of range. I forget the exact values, it was a few days ago.

The scanner gives separate readings for each of the four oxygen sensors. My problem is that I can't figure out which data point on the scanner refers to which oxygen sensor. The scanner gives me 8 different readouts that I can cycle through: SF1, SF2, SF3, SF4 (short term fuel trims) and LF1, LF2, LF3, LF4 (long term fuel trims). The readings on data points 1 and 2 are low single digits, the readings on data points 3 and 4 are higher. Since I'm already getting an OBD code I'm inferring that the downstream driver's side (P0138) corresponds with either SF3/LF3 or SF4/LF4. Beyond that I can't pinpoint which is which.

The user's manual doesn't give any information about which data point goes with which sensor. I'd appreciate any insight that helps me identify what goes with what. Perhaps the ScanGauge manual has this info and the data points are the same across tools.
 

WaltNYC

Well-known member
Mar 3, 2010
707
135
NYC
Save yourself the anxiety, doubt, bandwidth and time (and maybe money) and get a dongle from Amazon and either Torque or OBD Fusion depending on what phone/device you use. For <$30 if will be the best money spent on your trucks.
 

jprover2

Well-known member
Apr 8, 2017
146
10
Birmingham,Al
You need to check voltage between your maximum lean to rich time. It should be 3.13 volts and 1.13 volts, the time between should be .349 seconds. Is there a misfire? Or just the MIL light on? Without knowing what the exact values are your seeing it's hard to know what you have going on.
 

ERover82

Well-known member
Nov 26, 2011
3,899
450
Darien Gap
Save yourself the anxiety, doubt, bandwidth and time (and maybe money) and get a dongle from Amazon and either Torque or OBD Fusion depending on what phone/device you use. For <$30 if will be the best money spent on your trucks.

What advantage is provided that his current reader doesn't reveal?
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
Is there a misfire? Or just the MIL light on? Without knowing what the exact values are your seeing it's hard to know what you have going on.

Engine is running smoothly. Other than variations in fuel trim data values the only indication that anything was amiss was the MIL. I'll check the fuse, thanks for the suggestion.
 

ERover82

Well-known member
Nov 26, 2011
3,899
450
Darien Gap
That's driver-side downstream O2 sensor. Downstream sensors aren't used for fuel ratio calculations. Only replace it if you care about emissions testing or looking at a MIL light.
 

Tugela

Well-known member
May 21, 2007
4,754
561
Seattle
That's driver-side downstream O2 sensor. Downstream sensors aren't used for fuel ratio calculations. Only replace it if you care about emissions testing or looking at a MIL light.


I'm getting code P0138 which relates to downstream driver's sensor. So regardless of fuel trim data I need to replace that sensor.
 

WaltNYC

Well-known member
Mar 3, 2010
707
135
NYC
What advantage is provided that his current reader doesn't reveal?

It seems to me that the interface is not particularly user friendly and the OP came here for help interpreting. His current set up may ultimately reveal the same data as a more contemporary dongle+app setup, but ease of use and/or interpretation is a real issue.

Additionally, the apps do a better job of displaying more data in ways that can be configured by the user. I have saved several different 'dashboards' on mine. Each shows me different data sets. For example, one may show various temps sensor readings and another may show long and short term fuel trims.

Additionally the app allows me to choose how I want to see that data by allowing me to configure the outputs as analog 'dial' gauges or simple digital read-out, or a combination of the two.

I now sound like some sort of dongle+app salesman, but I have no skin in the game. It really boils down to ease of use which leads to effectiveness.

Everyone is different and if another system floats your boat, so be it. It's all good.
 

WaltNYC

Well-known member
Mar 3, 2010
707
135
NYC
I'm getting code P0138 which relates to downstream driver's sensor. So regardless of fuel trim data I need to replace that sensor.

I've had that same code a couple of times in the past six months. Both times I've simply cleared the code and it has taken quite some time for it to return (3-4 months). Could just be a connector is not 100% fully seated or something as simple as that. I do have a sensor on hand if/when it becomes persistent.