What is the difference between long term and short term fuel trim?
Long-term fuel trim relies on sensors further downstream in the exhaust system, past the catalytic converter. While the sensors’ signal will fluctuate frequently upstream, where short-term fuel trim is measured, the signal at the sensors further down should be fairly constant.
What is a rich fuel trim?
Fuel Trim is the adjustment the engine computer (PCM) makes to the fuel mixture to maintain a balanced air/fuel ratio. Fuel trim is usually displayed as a PERCENTAGE reading on a scan tool. A rich fuel mixture can produce more power (up to a point) but it also increases fuel consumption and emissions.
What is the difference between long-term and short term fuel trim?
How do I reset my short-term fuel trim?
To perform a PCM reset…
- Bring car up to normal operating temp.
- Turn ignition off.
- Remove ECM main fuse.
- Turn ignition to “on”, do not start.
- Wait for system check to complete, numerous errors will be detected.
- Turn ignition off.
- Replace fuse.
- Turn ignition to “on” and wait for system check.
What should the bank rich be on fuel trim?
The fuel trim values would be on the negative side and we would likely have a P0172/P0175 (Bank 1 and 2 Rich). Clogged or contaminated injectors should be checked, but only after diagnosing the components listed in the previous paragraph.
When to use short term and long term fuel trims?
If you connect a scan tool to such a vehicle, both the short and long-term fuel trim data will be displayed as percentages. Ideally, both values should be at, or close to 0%, when the engine is running at a steady speed, such as when it is idling.
How does fuel trim work on a PCM?
Fuel Trim is the ECM/PCM’s programmed response to perceived rich or lean conditions as reported by the Oxygen Sensor (s). Short term and long term fuel trim are usually displayed as a percentage; the scale is laid out like a number line, with zero in the middle, positive numbers on the right, and negative numbers on the left.
What happens if my fuel trim is too big?
If a Long-Term Fuel Trim get too large (±25%), the PCM/ECM will trigger a “MIL” warning, and set one or more Data Troubles Codes (DTC) to help diagnose the problem. The DTCs directly related to fuel trim problems are: