What does it mean when your fuel trim is negative?
Rich codes and the drivability issues that accompany a rich running condition would be reflected with negative fuel trim numbers: an indication the PCM is subtracting fuel. Leaking injectors, broken fuel pressure diagrams, improper fuel pressure and skewed sensor readings are a few examples of issues that could result in a rich running condition.
What are the fault codes for fuel trim?
Fig. 1 above shows the fuel trim data collected on a vehicle with the Check Engine light on and fault codes P0171 (Bank 1 System Lean) and P0174 (Bank 2 System Lean) present.
When to check fuel trim for engine failure?
Some general guidelines for diagnosing fuel trim and the potential causes for failure can be found below. A useful diagnostic tool is to determine if the fuel trim problem exists in more than one engine operating range. Fuel trim should be checked at idle, at 1,500 rpm and at 2,500 rpm.
How do you baseline the fuel trim data?
Baselining the fuel trim data is a simple four-step diagnostic process: 1. Connect an OBD II generic scan tool, preferably with recording capabilities. 2. Monitor and record the fuel trim values in the four common operating ranges—idle speed, light load (20 to 30 mph), moderate load (40 to 50 mph) and heavy load (60 to 70 mph). 3.
Why is my fuel trim on the negative side?
Leaking or contaminated fuel injectors were listed as possible causes for these fault codes, but leaking fuel injectors would create a richer-than-normal air/fuel mixture. The fuel trim values would be on the negative side and we would likely have a P0172/P0175 (Bank 1 and 2 Rich).
Some general guidelines for diagnosing fuel trim and the potential causes for failure can be found below. A useful diagnostic tool is to determine if the fuel trim problem exists in more than one engine operating range. Fuel trim should be checked at idle, at 1,500 rpm and at 2,500 rpm.
When did fuel trim cut diagnostic time in half?
No matter what the driveability issue happens to be, checking the PCM’s fuel trim decisions first can get you pointed in the right direction, and may end up cutting your diagnostic time in half. The year is 2006, and for those who may have overlooked it, this is the 10th anniversary of On-Board Diagnostics II (OBD II).
Fig. 1 above shows the fuel trim data collected on a vehicle with the Check Engine light on and fault codes P0171 (Bank 1 System Lean) and P0174 (Bank 2 System Lean) present.