Short term fuel trim

Tiny
KEITH RICHARDSON
  • MEMBER
  • 2003 CADILLAC DEVILLE
  • 128,000 MILES
When I run my car to temperature and plug my meter in the short term fuel trim B1S2 reads 99.2%. Is this correct or what does this mean?
Tuesday, October 22nd, 2019 AT 8:21 AM

8 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
Welcome back to 2CarPros. That cannot be the actual fuel trim number. I would say whatever you are using to read the data is either reading the wrong signal or it is reading it inverted. Normal short term fuel trims on a good running engine will be around 1%. It also wouldn't be expressed as Bank 1 Sensor 2, but only as bank one or bank two.
B1S2 would be a designation for an oxygen sensor, but they don't read in percentage but in voltage.
What is the scan tool you are using?
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Wednesday, October 23rd, 2019 AT 7:25 AM
Tiny
KEITH RICHARDSON
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  • 6 POSTS
This is the scan tool and the reading.
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Wednesday, October 23rd, 2019 AT 9:32 AM
Tiny
STEVE W.
  • MECHANIC
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Launch has extra data PIDs in many of their tools. In this case it looks like they are reading something else. Notice that B1S1 is reading 0%. Is this with the engine running? If yes I would say it's extraneous data. The reason for that is that short and long term fuel trims both max out at around 24% on GM engines. 99% would flood the engine with fuel to the point it wouldn't run.
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Wednesday, October 23rd, 2019 AT 11:59 AM
Tiny
KEITH RICHARDSON
  • MEMBER
  • 6 POSTS
Running at idle. Here are some other readings. Do they look okay?
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Wednesday, October 23rd, 2019 AT 1:00 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
It looks like it isn't fully warmed up. Looks to be in open loop so that makes many of the readings more or less unknowns. Until it goes into closed loop. But the ones on there look okay.
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Wednesday, October 23rd, 2019 AT 3:57 PM
Tiny
KEITH RICHARDSON
  • MEMBER
  • 6 POSTS
Thanks for the information.
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Wednesday, October 23rd, 2019 AT 4:47 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
No problem. Take it out for a drive, once it's warm capture that data and post it here. Might see if it's good or not.
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Wednesday, October 23rd, 2019 AT 6:43 PM
Tiny
KEITH RICHARDSON
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  • 6 POSTS
Will do.
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Wednesday, October 23rd, 2019 AT 7:25 PM

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